The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlin...The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlinear flow control by interaction between two flexible flaps is proposed,and their flow control mechanism is studied employing the self-constructed immersed boundary-lattice Boltzmann-finite element method(IB-LB-FEM).The effects of the difference in material properties and flap length between the two flexible flaps on the nonlinear flow control of the airfoil are discussed.It is suggested that the relationship between the deformation of the two flexible flaps and the evolution of the vortex under the fluid-structure interaction(FSI).It is shown that the upstream flexible flap plays a key role in the flow control of the two flexible flaps.The FSI effect of the upstream flexible flap will change the unsteady flow behind it and affect the deformation of the downstream flexible flap.Two flexible flaps with different material properties and different lengths will change their own FSI characteristics by the induced vortex,effectively suppressing the flow separation on the airfoil’s upper surface.The interaction of two flexible flaps plays an extremely important role in improving the autonomy and adjustability of flow control.The numerical results will provide a theoretical basis and technical guidance for the development and application of a new flap passive control technology.展开更多
Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulat...Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulate the typical gas-liquid two-phase fow patterns.First,validation of the numerical model is conducted and the typical fow patterns are consistent with the Baker chart.Then,the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase fow.The results show that the dynamic response under stratified fow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively.Meanwhile,the dynamic responses induced by slug fow,wave fow and annular fow show obvious periodic fuctuations.Furthermore,the dynamic response characteristics under slug flow condition are maximum;the maximum pipe deformation and equivalent stress can reach 4mm and 17.5 MPa,respectively.The principal direction of total deformation is different under various flow patterns.Therefore,the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe.The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions.展开更多
Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.Ho...Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.展开更多
Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational ...Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational pumping effect, mainstream pressure asymmetry, rotor–stator interaction,and unsteady flow structures, complicating the flow. To investigate the impact of rotor–stator interaction on ingestion, this paper decouples the model to include only the mainstream. This research employs experiments and numerical simulations to examine the effects of varying the flow coefficient through changes in rotational speed and mainstream flow rate. The main objective is to understand the influence of different rotor–stator interactions on the mainstream pressure field, accompanied by mechanistic explanations. The findings reveal inconsistent effects of the two methods for changing the flow coefficient on the mainstream pressure field. Particularly, the pressure distribution on the vane side primarily depends on the mainstream flow rate, while the pressure on the blade side is influenced by the mainstream flow rate and the attack angle represented by the flow coefficient. A larger angle of attack angle can increase pressure on the blade side, even surpassing the pressure on the vane side. Assessing the degree of mainstream pressure unevenness solely based on the pressure difference on the vane side is insufficient. This research provides a basis for subsequent studies on the influence of coupled real turbine rotor–stator interaction on gas ingestion.展开更多
Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and p...Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and poor heat resistance limit their application scope.Recent advances have highlighted that the combination of extensional flow and thermal fields can achieve toughness–stiffness balance,high transparency,and good heat resistance.However,the effect of extensional flow on the post-non-isothermal crystallization of PLLA during heating and the resulting crystalline texture remains unclear.In this study,PLLA with a heterogeneous amorphous structure and oriented polymorph was prepared by extensional flow.The effect of heterogeneous amorphous structures on non-isothermal crystallization kinetics during the heating process was studied by thermal analysis,polarized optical microscopy,infrared spectroscopy,and ex situ/in situ X-ray characterization.These results clearly illustrate that extensional flow enhances the formation of oriented crystalline structures,accelerates non-isothermal crystallization,and modulates the polymorphic composition of PLLA.Moreover,an unexpected dual cold-crystallization behavior is identified in ordered PLLA samples upon extensional flow,which is from the extensional flow-induced heterogeneous amorphous phase into α' phase(low-temperature peak)and the pristine amorphous phase intoαphase(high-temperature peak).The extensional flow primarily promotes the formation of the more perfectαandα'phases,but has a negative effect on the final content ofαphase formed after cold crystallization andα'-to-αphase transformation.The findings of this work advance the understanding of PLLA non-isothermal crystallization after extensional flow and offer valuable guidance for high-performance PLLA upon heat treatment in practical processing.展开更多
The sluggish electrochemical catalytic activity of the graphite felt electrodes for anode reaction is still a barrier for achieving high-performance vanadium redox flow battery(VRFB).It is significant to leverage the ...The sluggish electrochemical catalytic activity of the graphite felt electrodes for anode reaction is still a barrier for achieving high-performance vanadium redox flow battery(VRFB).It is significant to leverage the exceptional conductivity,excellent electrocatalytic activity,and structural tunability of MXene to address this issue.Herein,this work introduces nitrogen atoms to modulate the carbon layer structure of Ti_(3)C_(2)T_(x)MXene,inducing a reconfiguration of the local electronic structure,which enhances the anode interface activity and thereby improves the performance of VRFB.Ti_(3)C_(2)T_(x)exhibits high conductivity,excellent hydrophilicity,and a large specific surface area,providing excellent interface characteristics for V^(3+)/V^(2+)redox reaction.Moreover,interlayer treatment to modulate the mesoporous structure of MXene further increases the reactive surface area.Importantly,doping nitrogen atoms at carbon layer induces lattice distortions in Ti_(3)C_(2)T_(x),which enhances the charge transfer processes of the V^(3+)/V^(2+)redox reaction.The catalysis mechanism is also validated through density functional theory.Furthermore,the modified graphite felt electrode,as the anode of VRFB,relieves a higher energy efficiency of 68%at 250 mA cm^(-2),while the pristine electrode cannot operate at this current density.In addition,at 150 mA cm^(-2),the modified battery maintains energy efficiency at 75%without degradation after 500 cycles.This study utilizes rational atomic-level engineering for effective structural modulation to significantly enhance the catalytic activity of electrode reaction,offering a unique perspective for developing high-performance MXene electrocatalysts of VRFB.展开更多
Certain insect species have been observed to exploit the resonance mechanism of their wings.In order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency...Certain insect species have been observed to exploit the resonance mechanism of their wings.In order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency of flexible wings based on the Traditional Structural Modal(TSM)analysis.However,there exists controversy among researchers regarding the relationship between frequency and aerodynamic performance.Recognizing that the structural response of wings can be influenced by the surrounding air vibrations,an analysis known as Acoustic Structure Interaction Modal(ASIM)is introduced to calculate the resonant frequency.In this study,Fluid Structure Interaction(FSI)simulations are employed to investigate the aerodynamic performance of flapping wings at modal frequencies derived from both TSM and ASIM analyses.The performance is evaluated for various mass ratios and frequency ratios,and the findings indicate that the deformation and changes in vortex structure exhibit similarities at mass ratios that yield the highest aerodynamic performance.Notably,the flapping frequency associated with the maximum time-averaged vertical force coefficient at each mass ratio closely aligns with the ASIM frequency,as does the frequency corresponding to maximum efficiency.Thus,the ASIM analysis can provide an effective means for predicting the optimal flapping frequency for flexible wings.Furthermore,it enables the prediction that flexible wings with varying mass ratios will exhibit similar deformation and vortex structure changes.This paper offers a fresh perspective on the ongoing debate concerning the resonance mechanism of Flexible Flapping Wings(FFWs)and proposes an effective methodology for predicting their aerodynamic performance.展开更多
The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flex...The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.展开更多
A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid ...A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid dynamics(CFD) approach, in which the unsteady, noncompressible Reynolds Averaged Navier-Stokes(RANS) method is used. The main focus of the study is to analyze the tower shadow effect on the aerodynamic performance of the wind turbine under different inlet flow conditions. Subsequently, the finite element model is established by considering fluid/structure interactions to study the structural stress, displacement, strain distributions and flow field information of the structure under the uniform wind speed. Finally, the fluid-structure interaction model is established by considering turbulent wind and the tower shadow effect. The variation rules of the dynamic response of the one-way and two-way fluid-structure interaction(FSI) models under different wind speeds are analyzed, and the numerical calculation results are compared with those of the centralized mass model. The results show that the tower shadow effect and structural deformation are the main factors affecting the aerodynamic load fluctuation of the wind turbine, which in turn affects the aerodynamic performance and structural stability of the blades. The structural dynamic response of the coupled model shows significant similarity, while the structural displacement response of the former exhibits less fluctuation compared with the conventional centralized mass model. The one-way fluid-structure interaction(FSI)model shows a higher frequency of stress-strain and displacement oscillations on the blade compared with the two-way FSI model.展开更多
Light–matter interactions in two-dimensional(2D)materials have been the focus of research since the discovery of graphene.The light–matter interaction length in 2D materials is,however,much shorter than that in bulk...Light–matter interactions in two-dimensional(2D)materials have been the focus of research since the discovery of graphene.The light–matter interaction length in 2D materials is,however,much shorter than that in bulk materials owing to the atomic nature of 2D materials.Plasmonic nanostructures are usually integrated with 2D materials to enhance the light–matter interactions,offering great opportunities for both fundamental research and technological applications.Nanoparticle-on-mirror(NPo M)structures with extremely confined optical fields are highly desired in this aspect.In addition,2D materials provide a good platform for the study of plasmonic fields with subnanometer resolution and quantum plasmonics down to the characteristic length scale of a single atom.A focused and up-to-date review article is highly desired for a timely summary of the progress in this rapidly growing field and to encourage more research efforts in this direction.In this review,we will first introduce the basic concepts of plasmonic modes in NPo M structures.Interactions between plasmons and quasi-particles in 2D materials,e.g.,excitons and phonons,from weak to strong coupling and potential applications will then be described in detail.Related phenomena in subnanometer metallic gaps separated by 2D materials,such as quantum tunneling,will also be touched.We will finally discuss phenomena and physical processes that have not been understood clearly and provide an outlook for future research.We believe that the hybrid systems of2D materials and NPo M structures will be a promising research field in the future.展开更多
Studies showed that complexation of polyphenols with milk allergens reduced their immunogenic potential.However,the relationship between structures of polyphenols and their hypoallergenic effects on milk allergens in ...Studies showed that complexation of polyphenols with milk allergens reduced their immunogenic potential.However,the relationship between structures of polyphenols and their hypoallergenic effects on milk allergens in association with physiological and conformational changes of the complexes remain unclear.In this study,polyphenols from eight botanical sources were extracted to prepare non-covalent complexes withβ-lactoglobulin(β-LG),a major allergen in milk.The dominant phenolic compounds bound toβ-LG with a diminished allergenicity were identified to investigate their respective role on the structural and allergenic properties ofβ-LG.Extracts from Vaccinium fruits and black soybeans were found to have great inhibitory effects on the IgE-and IgG-binding abilities ofβ-LG.Among the fourteen structure-related phenolic compounds,flavonoids and tannins with larger MWs and multi-hydroxyl substituents,notably rutin,EGCG,and ellagitannins were more potent to elicit changes on the conformational structures ofβ-LG to decrease the allergenicity of complexedβ-LG.Correlation analysis further demonstrated that a destabilized secondary structure and protein depolymerization caused by polyphenol-binding were closely related to the allergenicity property of formed complexes.This study provides insights into the understanding of structure-allergenicity relationship ofβ-LG-polyphenol interactions and would benefit the development of polyphenol-fortified matrices with hypoallergenic potential.展开更多
Fluid-structure-particle interactions in three spatial dimensions happen in many environmental and engineering flows.This paper presents the parallel algorithms for the hybrid diffuse and sharp interface immersed boun...Fluid-structure-particle interactions in three spatial dimensions happen in many environmental and engineering flows.This paper presents the parallel algorithms for the hybrid diffuse and sharp interface immersed boundary(IB)method developed in our previous work.For the moving structure modeled using the sharp interface IB method,a recursive box method is developed for efficiently classifying the background grid nodes.For the particles modeled using the diffuse interface IB method,a‘master-slave’approach is adopted.For the particle-particle interaction(PPI)and particle-structure interaction(PSI),a fast algorithm for classifying the active and inactive Lagrangian points,which discretize the particle surface,is developed for the‘dry’contact approach.The results show that the proposed recursive box method can reduce the classifying time from 52seconds to 0.3 seconds.Acceptable parallel efficiency is obtained for cases with different particle concentrations.Furthermore,the lubrication model is utilized when a particle approaches a wall,enabling an accurate simulation of the rebounding phenomena in the benchmark particle-wall collision problem.At last,the capability of the proposed computational framework is demonstrated by simulating particle-laden turbulent channel flows with rough walls.展开更多
Unsteady currents fluids flowing through a baffle with holes found in a mobile storage tank are complex to analyze. This study aims to evaluate the effects of fluid structure interactions (FSI) on baffles in tanks car...Unsteady currents fluids flowing through a baffle with holes found in a mobile storage tank are complex to analyze. This study aims to evaluate the effects of fluid structure interactions (FSI) on baffles in tanks carried on mobile trucks that, more often than not, experience sloshing phenomenon engulfed by turbulences behaviors with respect to different motions of the truck. Mindful of the different types of baffles that are used in the tanks to limit sloshing wave activities and improve safety by allowing fluid to pass through carefully designed holes that are also placed in a specific pattern, the fluid structure interaction around a baffle with a hole is evaluated here through computing. Passing through the solver in COMSOL, an equivalent design tank and baffle with a hole is discretized to point form such that the fluid flowing through each point is evaluated and interpreted on a point graph generated with respect to each point located on the tank or baffle hole. The result obtained not only shows the effects of FSI as a function of turbulence kinetic energy per individual point but also the contour pressure field and velocity magnitude of the entire system.展开更多
Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simpli...Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics （CFD）-fluid structure interaction （FSI） techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called ＂dynamic mesh＂ technique. A new mesh movement approacb is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the joumal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function （UDF）. The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.展开更多
This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles a...This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles are analyzed synchronously using FLUENT software, and the effects of fluid-structure interaction on the performance of the labyrinth seal are revealed. The results indicate that with the growth of tooth profile angle, the leakage rate of labyrinth seal tends to decrease first, and then increase. The results of fluid-structure interaction analysis are close to those of actual engineering. The effect of fluid-structure interaction makes tiny deformation in calculation mesh of piston and cylinder structure, and the coupling interaction affects the performance of the labyrinth seal.展开更多
Cities separated in space are connected together by spatial interaction (SI) between them. But the studies focusing on the SI are relatively few in China mainly because of the scarcity of data. This paper deals with t...Cities separated in space are connected together by spatial interaction (SI) between them. But the studies focusing on the SI are relatively few in China mainly because of the scarcity of data. This paper deals with the SI in terms of rail passenger flows, which is an important aspect of the network structure of urban agglomeration. By using a data set consisting of rail O-D (origin-destination) passenger flows among nearly 200 cities, intercity rail distance O-D matrixes, and some other indices, it is found that the attenuating tendency of rail passenger is obvious. And by the analysis on dominant flows and spatial structure of flows, we find that passenger flows have a trend of polarizing to hubs while the linkages between hubs upgrade. However, the gravity model reveals an overall picture of convergence process over time which is not in our expectation of integration process in the framework of globalization and economic integration. Some driven factors for the re-organization process of the structure of urban agglomeration, such as technique advance, globalization, etc. are discussed further based on the results we obtained.展开更多
Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patte...Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patterns and turbulence were modelled by using the volume of fluid(VOF)model and the Realizable k−εturbulence model respectively.Firstly,validation of the CFD model was carried out and the desirable results were obtained.The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data.Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow.Then,a one-way coupled fluid-structure interaction framework was established to investigate the slug flow interaction with a 90°pipe bend under various superficial liquid and gas velocities.It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity,while decreased with the increasing superficial liquid velocity.In addition,the total deformation and equivalent stress has obvious periodic fluctuation.Furthermore,the distribution position of maximum deformation and stress was related to the evolution of slug flow.With the increasing superficial gas velocity,the maximum total deformation was mainly located at the 90°pipe bend.But as the superficial liquid velocity increases,the maximum total deformation was mainly located in the horizontal pipe section.Consequently,the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90°pipe bend.展开更多
Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)mode...Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)models were introduced to perform ventricle mechanical analysis,investigate flow behaviors,and evaluate the impact of myocardial infarction(MI)and hypertension on blood flow in the LV.Echo image data were acquired from 3 patients with consent obtained:one healthy volunteer(P1),one hypertension patient(P2),and one patient who had an inferior and posterior myocardial infarction(P3).The nonlinear Mooney-Rivlin model was used for ventricle tissue with material parameter values chosen to match echo-measure LV volume data.Using the healthy case as baseline,LV with MI had lower peak flow velocity(30%lower at beginejection)and hypertension LV had higher peak flow velocity(16%higher at begin-filling).The vortex area(defined as the area with vorticity>0)for P3 was 19%smaller than that of P1.The vortex area for P2 was 12%smaller than that of P1.At peak of filling,the maximum flow shear stress(FSS)for P2 and P3 were 390%higher and 63%lower than that of P1,respectively.Meanwhile,LV stress and strain of P2 were 41%and 15%higher than those of P1,respectively.LV stress and strain of P3 were 36%and 42%lower than those of P1,respectively.In conclusion,FSI models could provide both flow and structural stress/strain information which would serve as the base for further cardiovascular investigations related to disease initiation,progression,and treatment strategy selections.Large-scale studies are needed to validate our findings.展开更多
An adaptive finite element method for high-speed flow-structure interaction is pre- sented.The cell-centered finite element method is combined with an adaptive meshing technique to solve the Navier-Stokes equations fo...An adaptive finite element method for high-speed flow-structure interaction is pre- sented.The cell-centered finite element method is combined with an adaptive meshing technique to solve the Navier-Stokes equations for high-speed compressible flow behavior.The energy equation and the quasi-static structural equations for aerodynamically heated structures are solved by applying the Galerkin finite element method.The finite element formulation and computational procedure are de- scribed.Interactions between the high-speed flow,structural heat transfer,and deformation are studied by two applications of Mach 10 flow over an inclined plate,and Mach 4 flow in a channel.展开更多
The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid ...The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.展开更多
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.92371201,52192633,11872293,and 92152301)the Natural Science Basic Research Program of Shaanxi(Grant Nos.2024JC-YBQN-0008,and 2022JC-03)+1 种基金Shaanxi Key Research and Development Program(Grant No.2022ZDLGY02-07)the Joint Natural Science Foundation of China with Guangdong Province for TianHe-II Supercomputer Resources,and the Research Start-up Foundation of Xi’an University of Science and Technology for the High-Level Talent.
文摘The flow control at low Reynolds numbers is one of the most promising technologies in the field of aerodynamics,and it is also an important source of the innovation for novel aircraft.In this study,a new way of nonlinear flow control by interaction between two flexible flaps is proposed,and their flow control mechanism is studied employing the self-constructed immersed boundary-lattice Boltzmann-finite element method(IB-LB-FEM).The effects of the difference in material properties and flap length between the two flexible flaps on the nonlinear flow control of the airfoil are discussed.It is suggested that the relationship between the deformation of the two flexible flaps and the evolution of the vortex under the fluid-structure interaction(FSI).It is shown that the upstream flexible flap plays a key role in the flow control of the two flexible flaps.The FSI effect of the upstream flexible flap will change the unsteady flow behind it and affect the deformation of the downstream flexible flap.Two flexible flaps with different material properties and different lengths will change their own FSI characteristics by the induced vortex,effectively suppressing the flow separation on the airfoil’s upper surface.The interaction of two flexible flaps plays an extremely important role in improving the autonomy and adjustability of flow control.The numerical results will provide a theoretical basis and technical guidance for the development and application of a new flap passive control technology.
基金the National Natural Science Foundation of China(No.51779143)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(No.SL2020ZD101)the Cultivation of Scientific Research Ability of Young Talents of Shanghai Jiao Tong University(No.19X100040072)。
文摘Fluid-structure interaction(FSI)of gas-liquid two-phase fow in the horizontal pipe is investigated numerically in the present study.The volume of fluid model and standard k-e turbulence model are integrated to simulate the typical gas-liquid two-phase fow patterns.First,validation of the numerical model is conducted and the typical fow patterns are consistent with the Baker chart.Then,the FSI framework is established to investigate the dynamic responses of the interaction between the horizontal pipe and gas-liquid two-phase fow.The results show that the dynamic response under stratified fow condition is relatively flat and the maximum pipe deformation and equivalent stress are 1.8 mm and 7.5 MPa respectively.Meanwhile,the dynamic responses induced by slug fow,wave fow and annular fow show obvious periodic fuctuations.Furthermore,the dynamic response characteristics under slug flow condition are maximum;the maximum pipe deformation and equivalent stress can reach 4mm and 17.5 MPa,respectively.The principal direction of total deformation is different under various flow patterns.Therefore,the periodic equivalent stress will form the cyclic impact on the pipe wall and affect the fatigue life of the horizontal pipe.The present study may serve as a reference for FSI simulation under gas-liquid two-phase transport conditions.
基金funded by the National Natural Science Foundation of China(Grant No.52276047)the Open Fund of NationalKey Laboratory of SpacecraftThermal Control(Grant No.NKLST-JJ-202401011)the Beijing Municipal Science&Technology Commission(Grant No.Z231100006123010).
文摘Flow boiling in open microchannels offers highly efficient heat transfer performance and has attracted increasing attention in the fields of heat transfer and thermalmanagement of electronic devices in recent years.However,the continuous rise in power density of electronic components imposesmore stringent requirements on the heat transfer capability of microchannel flow boiling.HFE-7100,a dielectric coolant with favorable thermophysical properties,has become a focal point of research for enhancing flow boiling performance in open microchannels.The flow boiling heat transfer performance ofHFE-7100 was investigated in this study by fabricating micro-nano composite structures on the bottom surface of open microchannels using laser ablation technology.Based on visualization results,a comparative analysis was conducted on the bubble dynamics and flow pattern characteristics of HFE-7100 flow boiling in micronano structured open microchannels(MNSOMC)and smooth-surface open microchannels(SSOMC),to elucidate the enhancement mechanism of micro-nano structures on flow boiling heat transfer in open microchannels.The results indicate that the surface structures and strong wettability of MNSOMC accelerated bubble nucleation and departure.Moreover,bubbles in the channel tended to coalesce along the flow direction,forming elongated slug bubbles with high aspect ratios,which enabled efficient thin film evaporation in conjunction with intense nucleate boiling,thereby significantly enhancing flow boiling heat transfer.Under the experimental conditions of this study,the maximum enhancements in the heat transfer coefficient(HTC)and critical heat flux(CHF)of HFE-7100 inMNSOMC were 33.4%and 133.1%,respectively,with the CHF reaching up to 1542.3 kW⋅m^(−2).Furthermore,due to the superior wettability and capillary wicking capability of the micro-nano composite structures,the significant enhancement in flow boiling heat transfer was achieved without incurring a noticeable pressure drop penalty.
基金the National Natural Science Foundation Outstanding Youth Foundation (Grant No.52122603)the National Science and Technology Major Project (J2019-Ⅲ-0003–0046)。
文摘Clarifying the gas ingestion mechanism in the turbine disc cavity of marine gas turbines is crucial for ensuring the normal operation of turbines.However, the ingestion is influenced by factors such as the rotational pumping effect, mainstream pressure asymmetry, rotor–stator interaction,and unsteady flow structures, complicating the flow. To investigate the impact of rotor–stator interaction on ingestion, this paper decouples the model to include only the mainstream. This research employs experiments and numerical simulations to examine the effects of varying the flow coefficient through changes in rotational speed and mainstream flow rate. The main objective is to understand the influence of different rotor–stator interactions on the mainstream pressure field, accompanied by mechanistic explanations. The findings reveal inconsistent effects of the two methods for changing the flow coefficient on the mainstream pressure field. Particularly, the pressure distribution on the vane side primarily depends on the mainstream flow rate, while the pressure on the blade side is influenced by the mainstream flow rate and the attack angle represented by the flow coefficient. A larger angle of attack angle can increase pressure on the blade side, even surpassing the pressure on the vane side. Assessing the degree of mainstream pressure unevenness solely based on the pressure difference on the vane side is insufficient. This research provides a basis for subsequent studies on the influence of coupled real turbine rotor–stator interaction on gas ingestion.
基金supported by the National Natural Science Foundation of China(Nos.U23A20583,52033005,U21A2090,and 52173040)Department of Science and Technology of Sichuan Province(No.2024NSFTD0003)。
文摘Poly(_(L)-lactide)(PLLA),a leading biodegradable polyester,has demonstrated potential as a sustainable alternative,owing to its excellent biodegradability and rigidity.However,their slow crystallization kinetics and poor heat resistance limit their application scope.Recent advances have highlighted that the combination of extensional flow and thermal fields can achieve toughness–stiffness balance,high transparency,and good heat resistance.However,the effect of extensional flow on the post-non-isothermal crystallization of PLLA during heating and the resulting crystalline texture remains unclear.In this study,PLLA with a heterogeneous amorphous structure and oriented polymorph was prepared by extensional flow.The effect of heterogeneous amorphous structures on non-isothermal crystallization kinetics during the heating process was studied by thermal analysis,polarized optical microscopy,infrared spectroscopy,and ex situ/in situ X-ray characterization.These results clearly illustrate that extensional flow enhances the formation of oriented crystalline structures,accelerates non-isothermal crystallization,and modulates the polymorphic composition of PLLA.Moreover,an unexpected dual cold-crystallization behavior is identified in ordered PLLA samples upon extensional flow,which is from the extensional flow-induced heterogeneous amorphous phase into α' phase(low-temperature peak)and the pristine amorphous phase intoαphase(high-temperature peak).The extensional flow primarily promotes the formation of the more perfectαandα'phases,but has a negative effect on the final content ofαphase formed after cold crystallization andα'-to-αphase transformation.The findings of this work advance the understanding of PLLA non-isothermal crystallization after extensional flow and offer valuable guidance for high-performance PLLA upon heat treatment in practical processing.
基金financially supported by the National Natural Science Foundation of China(51872090,51772097)Hebei Natural Science Fund for Distinguished Young Scholar(E2019209433)+3 种基金Youth Talent Program of Hebei Provincial Education Department(BJ2018020)Natural Science Foundation of Hebei Province(E2020209151,E2024209029)National Key R&D Plan Project(2022YFB4200305)Research Projects of China National Petroleum Corporation(2024ZG50,2023DQ03-04)。
文摘The sluggish electrochemical catalytic activity of the graphite felt electrodes for anode reaction is still a barrier for achieving high-performance vanadium redox flow battery(VRFB).It is significant to leverage the exceptional conductivity,excellent electrocatalytic activity,and structural tunability of MXene to address this issue.Herein,this work introduces nitrogen atoms to modulate the carbon layer structure of Ti_(3)C_(2)T_(x)MXene,inducing a reconfiguration of the local electronic structure,which enhances the anode interface activity and thereby improves the performance of VRFB.Ti_(3)C_(2)T_(x)exhibits high conductivity,excellent hydrophilicity,and a large specific surface area,providing excellent interface characteristics for V^(3+)/V^(2+)redox reaction.Moreover,interlayer treatment to modulate the mesoporous structure of MXene further increases the reactive surface area.Importantly,doping nitrogen atoms at carbon layer induces lattice distortions in Ti_(3)C_(2)T_(x),which enhances the charge transfer processes of the V^(3+)/V^(2+)redox reaction.The catalysis mechanism is also validated through density functional theory.Furthermore,the modified graphite felt electrode,as the anode of VRFB,relieves a higher energy efficiency of 68%at 250 mA cm^(-2),while the pristine electrode cannot operate at this current density.In addition,at 150 mA cm^(-2),the modified battery maintains energy efficiency at 75%without degradation after 500 cycles.This study utilizes rational atomic-level engineering for effective structural modulation to significantly enhance the catalytic activity of electrode reaction,offering a unique perspective for developing high-performance MXene electrocatalysts of VRFB.
基金This study was co-supported by the National Natural Science Foundation of China(No.52275293)the Guangdong Basic and Applied Basic Research Foundation,China(No.2023A1515010774)+1 种基金the Basic Research Program of Shenzhen,China(No.JCYJ 20190806142816524)the National Key Laboratory of Science and Technology on Aerodynamic Design and Research,China(No.61422010301).
文摘Certain insect species have been observed to exploit the resonance mechanism of their wings.In order to achieve resonance and optimize aerodynamic performance,the conventional approach is to set the flapping frequency of flexible wings based on the Traditional Structural Modal(TSM)analysis.However,there exists controversy among researchers regarding the relationship between frequency and aerodynamic performance.Recognizing that the structural response of wings can be influenced by the surrounding air vibrations,an analysis known as Acoustic Structure Interaction Modal(ASIM)is introduced to calculate the resonant frequency.In this study,Fluid Structure Interaction(FSI)simulations are employed to investigate the aerodynamic performance of flapping wings at modal frequencies derived from both TSM and ASIM analyses.The performance is evaluated for various mass ratios and frequency ratios,and the findings indicate that the deformation and changes in vortex structure exhibit similarities at mass ratios that yield the highest aerodynamic performance.Notably,the flapping frequency associated with the maximum time-averaged vertical force coefficient at each mass ratio closely aligns with the ASIM frequency,as does the frequency corresponding to maximum efficiency.Thus,the ASIM analysis can provide an effective means for predicting the optimal flapping frequency for flexible wings.Furthermore,it enables the prediction that flexible wings with varying mass ratios will exhibit similar deformation and vortex structure changes.This paper offers a fresh perspective on the ongoing debate concerning the resonance mechanism of Flexible Flapping Wings(FFWs)and proposes an effective methodology for predicting their aerodynamic performance.
基金supported by the National Natural Science Foundation of China(Nos.52192633,11872293)the Natural Science Foundation of Shaanxi Province,China(No.2022JC-03)。
文摘The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.
基金supported by the National Natural Science Foundation of China(Grant No.52078010)Beijing Natural Science Foundation(Grant No.JQ19029).
文摘A 5-MW wind turbine has been modeled and analyzed for fluid-structure interaction and aerodynamic performance.In this study, a full-scale model of a 5-MW wind turbine is first developed based on a computational fluid dynamics(CFD) approach, in which the unsteady, noncompressible Reynolds Averaged Navier-Stokes(RANS) method is used. The main focus of the study is to analyze the tower shadow effect on the aerodynamic performance of the wind turbine under different inlet flow conditions. Subsequently, the finite element model is established by considering fluid/structure interactions to study the structural stress, displacement, strain distributions and flow field information of the structure under the uniform wind speed. Finally, the fluid-structure interaction model is established by considering turbulent wind and the tower shadow effect. The variation rules of the dynamic response of the one-way and two-way fluid-structure interaction(FSI) models under different wind speeds are analyzed, and the numerical calculation results are compared with those of the centralized mass model. The results show that the tower shadow effect and structural deformation are the main factors affecting the aerodynamic load fluctuation of the wind turbine, which in turn affects the aerodynamic performance and structural stability of the blades. The structural dynamic response of the coupled model shows significant similarity, while the structural displacement response of the former exhibits less fluctuation compared with the conventional centralized mass model. The one-way fluid-structure interaction(FSI)model shows a higher frequency of stress-strain and displacement oscillations on the blade compared with the two-way FSI model.
基金supported by the National Natural Science Foundation of China(62205183)the Research Grants Council of Hong Kong(ANR/RGC,Ref.No.A-CUHK404/21).
文摘Light–matter interactions in two-dimensional(2D)materials have been the focus of research since the discovery of graphene.The light–matter interaction length in 2D materials is,however,much shorter than that in bulk materials owing to the atomic nature of 2D materials.Plasmonic nanostructures are usually integrated with 2D materials to enhance the light–matter interactions,offering great opportunities for both fundamental research and technological applications.Nanoparticle-on-mirror(NPo M)structures with extremely confined optical fields are highly desired in this aspect.In addition,2D materials provide a good platform for the study of plasmonic fields with subnanometer resolution and quantum plasmonics down to the characteristic length scale of a single atom.A focused and up-to-date review article is highly desired for a timely summary of the progress in this rapidly growing field and to encourage more research efforts in this direction.In this review,we will first introduce the basic concepts of plasmonic modes in NPo M structures.Interactions between plasmons and quasi-particles in 2D materials,e.g.,excitons and phonons,from weak to strong coupling and potential applications will then be described in detail.Related phenomena in subnanometer metallic gaps separated by 2D materials,such as quantum tunneling,will also be touched.We will finally discuss phenomena and physical processes that have not been understood clearly and provide an outlook for future research.We believe that the hybrid systems of2D materials and NPo M structures will be a promising research field in the future.
基金supported by the Zhejiang Provincial Natural Science Foundation of China(LGN22C200027 and LZ23C200001).
文摘Studies showed that complexation of polyphenols with milk allergens reduced their immunogenic potential.However,the relationship between structures of polyphenols and their hypoallergenic effects on milk allergens in association with physiological and conformational changes of the complexes remain unclear.In this study,polyphenols from eight botanical sources were extracted to prepare non-covalent complexes withβ-lactoglobulin(β-LG),a major allergen in milk.The dominant phenolic compounds bound toβ-LG with a diminished allergenicity were identified to investigate their respective role on the structural and allergenic properties ofβ-LG.Extracts from Vaccinium fruits and black soybeans were found to have great inhibitory effects on the IgE-and IgG-binding abilities ofβ-LG.Among the fourteen structure-related phenolic compounds,flavonoids and tannins with larger MWs and multi-hydroxyl substituents,notably rutin,EGCG,and ellagitannins were more potent to elicit changes on the conformational structures ofβ-LG to decrease the allergenicity of complexedβ-LG.Correlation analysis further demonstrated that a destabilized secondary structure and protein depolymerization caused by polyphenol-binding were closely related to the allergenicity property of formed complexes.This study provides insights into the understanding of structure-allergenicity relationship ofβ-LG-polyphenol interactions and would benefit the development of polyphenol-fortified matrices with hypoallergenic potential.
基金Project supported by the National Natural Science Foundation of China(Nos.12202456 and12172360)the Basic Science Center Program for“Multiscale Problems in Nonlinear Mechanics”of the National Natural Science Foundation of China(No.11988102)the China Postdoctoral Science Foundation(No.2021M693241)。
文摘Fluid-structure-particle interactions in three spatial dimensions happen in many environmental and engineering flows.This paper presents the parallel algorithms for the hybrid diffuse and sharp interface immersed boundary(IB)method developed in our previous work.For the moving structure modeled using the sharp interface IB method,a recursive box method is developed for efficiently classifying the background grid nodes.For the particles modeled using the diffuse interface IB method,a‘master-slave’approach is adopted.For the particle-particle interaction(PPI)and particle-structure interaction(PSI),a fast algorithm for classifying the active and inactive Lagrangian points,which discretize the particle surface,is developed for the‘dry’contact approach.The results show that the proposed recursive box method can reduce the classifying time from 52seconds to 0.3 seconds.Acceptable parallel efficiency is obtained for cases with different particle concentrations.Furthermore,the lubrication model is utilized when a particle approaches a wall,enabling an accurate simulation of the rebounding phenomena in the benchmark particle-wall collision problem.At last,the capability of the proposed computational framework is demonstrated by simulating particle-laden turbulent channel flows with rough walls.
文摘Unsteady currents fluids flowing through a baffle with holes found in a mobile storage tank are complex to analyze. This study aims to evaluate the effects of fluid structure interactions (FSI) on baffles in tanks carried on mobile trucks that, more often than not, experience sloshing phenomenon engulfed by turbulences behaviors with respect to different motions of the truck. Mindful of the different types of baffles that are used in the tanks to limit sloshing wave activities and improve safety by allowing fluid to pass through carefully designed holes that are also placed in a specific pattern, the fluid structure interaction around a baffle with a hole is evaluated here through computing. Passing through the solver in COMSOL, an equivalent design tank and baffle with a hole is discretized to point form such that the fluid flowing through each point is evaluated and interpreted on a point graph generated with respect to each point located on the tank or baffle hole. The result obtained not only shows the effects of FSI as a function of turbulence kinetic energy per individual point but also the contour pressure field and velocity magnitude of the entire system.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2009AA04Z413)Zhejiang Provincial Natural Science Foundation of China (Grant No. Y1110109)
文摘Journal bearings are important parts to keep the high dynamic performance of rotor machinery. Some methods have already been proposed to analysis the flow field of journal bearings, and in most of these methods simplified physical model and classic Reynolds equation are always applied. While the application of the general computational fluid dynamics （CFD）-fluid structure interaction （FSI） techniques is more beneficial for analysis of the fluid field in a journal bearing when more detailed solutions are needed. This paper deals with the quasi-coupling calculation of transient fluid dynamics of oil film in journal bearings and rotor dynamics with CFD-FSI techniques. The fluid dynamics of oil film is calculated by applying the so-called ＂dynamic mesh＂ technique. A new mesh movement approacb is presented while the dynamic mesh models provided by FLUENT are not suitable for the transient oil flow in journal bearings. The proposed mesh movement approach is based on the structured mesh. When the joumal moves, the movement distance of every grid in the flow field of bearing can be calculated, and then the update of the volume mesh can be handled automatically by user defined function （UDF）. The journal displacement at each time step is obtained by solving the moving equations of the rotor-bearing system under the known oil film force condition. A case study is carried out to calculate the locus of the journal center and pressure distribution of the journal in order to prove the feasibility of this method. The calculating results indicate that the proposed method can predict the transient flow field of a journal bearing in a rotor-bearing system where more realistic models are involved. The presented calculation method provides a basis for studying the nonlinear dynamic behavior of a general rotor-bearing system.
基金the Science and Technology Projects of Liaoning Province(No.2012219020)the China Postdoctoral Science Foundation(No.2013M541249)
文摘This paper addresses the issue of reciprocating compressors staggered labyrinth seal structure. The internal flow field of sealed structure, the displacement of cylinder and piston for different tooth profile angles are analyzed synchronously using FLUENT software, and the effects of fluid-structure interaction on the performance of the labyrinth seal are revealed. The results indicate that with the growth of tooth profile angle, the leakage rate of labyrinth seal tends to decrease first, and then increase. The results of fluid-structure interaction analysis are close to those of actual engineering. The effect of fluid-structure interaction makes tiny deformation in calculation mesh of piston and cylinder structure, and the coupling interaction affects the performance of the labyrinth seal.
基金Under the auspices of Key Project of National Natural Science Foundation of China (No 40635026)
文摘Cities separated in space are connected together by spatial interaction (SI) between them. But the studies focusing on the SI are relatively few in China mainly because of the scarcity of data. This paper deals with the SI in terms of rail passenger flows, which is an important aspect of the network structure of urban agglomeration. By using a data set consisting of rail O-D (origin-destination) passenger flows among nearly 200 cities, intercity rail distance O-D matrixes, and some other indices, it is found that the attenuating tendency of rail passenger is obvious. And by the analysis on dominant flows and spatial structure of flows, we find that passenger flows have a trend of polarizing to hubs while the linkages between hubs upgrade. However, the gravity model reveals an overall picture of convergence process over time which is not in our expectation of integration process in the framework of globalization and economic integration. Some driven factors for the re-organization process of the structure of urban agglomeration, such as technique advance, globalization, etc. are discussed further based on the results we obtained.
基金sponsored by the National Natural Science Foundation of China(Grant No.51779143)the Oceanic Interdisciplinary Program of Shanghai Jiao Tong University(Grant No.SL2020ZD101)the Cultivation of Scientific Research Ability of Young Talents of Shanghai Jiao Tong University(Grant No.19X100040072).
文摘Numerical simulations of evolution characteristics of slug flow across a 90°pipe bend have been carried out to study the fluid−structure interaction response induced by internal slug flow.The two-phase flow patterns and turbulence were modelled by using the volume of fluid(VOF)model and the Realizable k−εturbulence model respectively.Firstly,validation of the CFD model was carried out and the desirable results were obtained.The different flow patterns and the time-average mean void fraction was coincident with the reported experimental data.Simulations of different cases of slug flow have been carried out to show the effects of superficial gas and liquid velocity on the evolution characteristics of slug flow.Then,a one-way coupled fluid-structure interaction framework was established to investigate the slug flow interaction with a 90°pipe bend under various superficial liquid and gas velocities.It was found that the maximum total deformation and equivalent stress increased with the increasing superficial gas velocity,while decreased with the increasing superficial liquid velocity.In addition,the total deformation and equivalent stress has obvious periodic fluctuation.Furthermore,the distribution position of maximum deformation and stress was related to the evolution of slug flow.With the increasing superficial gas velocity,the maximum total deformation was mainly located at the 90°pipe bend.But as the superficial liquid velocity increases,the maximum total deformation was mainly located in the horizontal pipe section.Consequently,the slug flow with higher superficial gas velocity will induce more serious cyclical impact on the 90°pipe bend.
文摘Understanding cardiac blood flow behaviors is of importance for cardiovascular research and clinical assessment of ventricle functions.Patient-specific Echo-based left ventricle(LV)fluid-structure interaction(FSI)models were introduced to perform ventricle mechanical analysis,investigate flow behaviors,and evaluate the impact of myocardial infarction(MI)and hypertension on blood flow in the LV.Echo image data were acquired from 3 patients with consent obtained:one healthy volunteer(P1),one hypertension patient(P2),and one patient who had an inferior and posterior myocardial infarction(P3).The nonlinear Mooney-Rivlin model was used for ventricle tissue with material parameter values chosen to match echo-measure LV volume data.Using the healthy case as baseline,LV with MI had lower peak flow velocity(30%lower at beginejection)and hypertension LV had higher peak flow velocity(16%higher at begin-filling).The vortex area(defined as the area with vorticity>0)for P3 was 19%smaller than that of P1.The vortex area for P2 was 12%smaller than that of P1.At peak of filling,the maximum flow shear stress(FSS)for P2 and P3 were 390%higher and 63%lower than that of P1,respectively.Meanwhile,LV stress and strain of P2 were 41%and 15%higher than those of P1,respectively.LV stress and strain of P3 were 36%and 42%lower than those of P1,respectively.In conclusion,FSI models could provide both flow and structural stress/strain information which would serve as the base for further cardiovascular investigations related to disease initiation,progression,and treatment strategy selections.Large-scale studies are needed to validate our findings.
基金The project supported by the Thailand Research Fund(TRF)
文摘An adaptive finite element method for high-speed flow-structure interaction is pre- sented.The cell-centered finite element method is combined with an adaptive meshing technique to solve the Navier-Stokes equations for high-speed compressible flow behavior.The energy equation and the quasi-static structural equations for aerodynamically heated structures are solved by applying the Galerkin finite element method.The finite element formulation and computational procedure are de- scribed.Interactions between the high-speed flow,structural heat transfer,and deformation are studied by two applications of Mach 10 flow over an inclined plate,and Mach 4 flow in a channel.
基金the financial support provided by the Office of Naval Research(ONR) through grant number N00014-09-1-1204 (managed by Dr. Ki-Han Kim)supported in part by the National Research Foundation of Korea (NRF)grant funded by the Korea government (MEST) through the GCRC-SOP Grant No. 2012-0004783
文摘The objective of this paper is to present and to validate a new hybrid coupling （HC） algorithm for modeling of fluid-structure interaction （FSI） in incompressible, viscous flows. The HC algorithm is able to avoid numerical instability issues associated with artificial added mass effects, which are often encountered by standard loosely coupled （LC） and tightly coupled （TC） algorithms, when modeling the FSI response of flexible structures in incompressible flow. The artificial added mass effect is caused by the lag in exchange of interfacial displacements and forces between the fluid and solid solvers in partitioned algorithms. The artificial added mass effect is much more prominent for light/flexible struc- tures moving in water, because the fluid forces are in the same order of magnitude as the solid forces, and because the speed at which numerical errors propagate in an incom- pressible fluid. The new HC algorithm avoids numerical instability issues associated with artificial added mass effects by embedding Theodorsen＇s analytical approximation of the hydroelastic forces in the solution process to obtain better initial estimates of the displacements. Details of the new HC algorithm are presented. Numerical validation studies are shown for the forced pitching response of a steel and a plastic hydrofoil. The results show that the HC algorithm is able to converge faster, and is able to avoid numerical insta- bility issues, compared to standard LC and TC algorithms, when modeling the transient FSI response of a plastic hydrofoil. Although the HC algorithm is only demonstrated for a NACA0009 hydrofoil subject to pure pitching motion, the method can be easily extended to model general 3-D FSI response and stability of complex, flexible structures in turbulent, incompressible, multiphase flows.
