In this paper,we investigate a(2+1)-dimensional variable-coefficient modified dispersive waterwave system in fluid mechanics.We prove the Painlevéintegrability for that system via the Painlevéanalysis.We fin...In this paper,we investigate a(2+1)-dimensional variable-coefficient modified dispersive waterwave system in fluid mechanics.We prove the Painlevéintegrability for that system via the Painlevéanalysis.We find some auto-B?cklund transformations for that system via the truncated Painlevéexpansions.Bilinear forms and N-soliton solutions are constructed,where N is a positive integer.We discuss the inelastic interactions,elastic interactions and soliton resonances for the two solitons.We also graphically demonstrate that the velocities of the solitons are affected by the variable coefficient of that system.展开更多
This paper is to investigate the extended(2+1)-dimensional Konopelchenko-Dubrovsky equations,which can be applied to describing certain phenomena in the stratified shear flow,the internal and shallow-water waves, plas...This paper is to investigate the extended(2+1)-dimensional Konopelchenko-Dubrovsky equations,which can be applied to describing certain phenomena in the stratified shear flow,the internal and shallow-water waves, plasmas and other fields.Painleve analysis is passed through via symbolic computation.Bilinear-form equations are constructed and soliton solutions are derived.Soliton solutions and interactions are illustrated.Bilinear-form Backlund transformation and a type of solutions are obtained.展开更多
Burgers-type equations can describe some phenomena in fluids,plasmas,gas dynamics,traffic,etc.In this paper,an integrable hierarchy covering the lattice Burgers equation is derived from a discrete spectral problem.N-f...Burgers-type equations can describe some phenomena in fluids,plasmas,gas dynamics,traffic,etc.In this paper,an integrable hierarchy covering the lattice Burgers equation is derived from a discrete spectral problem.N-fold Darboux transformation(DT) and conservation laws for the lattice Burgers equation are constructed based on its Lax pair.N-soliton solutions in the form of Vandermonde-like determinant are derived via the resulting DT with symbolic computation,structures of which are shown graphically.Coexistence of the elastic-inelastic interaction among the three solitons is firstly reported for the lattice Burgers equation,even if the similar phenomenon for certern continuous systems is known.Results in this paper might be helpful for understanding some ecological problems describing the evolution of competing species and the propagation of nonlinear waves in fluids.展开更多
This paper is to investigate a variable-coefficient modified Kortweg-de Vries （vc-mKdV） model, which describes some situations from fluid mechanics, ocean dynamics, and plasma mechanics. By the AblowRz-Kaup-NewellSe...This paper is to investigate a variable-coefficient modified Kortweg-de Vries （vc-mKdV） model, which describes some situations from fluid mechanics, ocean dynamics, and plasma mechanics. By the AblowRz-Kaup-NewellSegur procedure and symbolic computation, the Lax pair of the vc-MKdV model is derived. Then, based on the aforementioned Lax pair, the Darboux transformation is constructed and a new one-soliton-like solution is obtained as weft Features of the one-soliton-like solution are analyzed and graphically discussed to illustrate the influence of the variable coefficients in the solitonlike propagation.展开更多
The Korteweg-de Vries(Kd V)-type equations have been seen in fluid mechanics,plasma physics and lattice dynamics,etc. This paper will address the bilinearization problem for some higher-order Kd V equations. Based on ...The Korteweg-de Vries(Kd V)-type equations have been seen in fluid mechanics,plasma physics and lattice dynamics,etc. This paper will address the bilinearization problem for some higher-order Kd V equations. Based on the relationship between the bilinear method and Bell-polynomial scheme,with introducing an auxiliary independent variable,we will present the general bilinear forms. By virtue of the symbolic computation,one-and two-soliton solutions are derived.展开更多
In bio-inspired flapping-wing flight,lift generation and flexible deformation are intrinsically coupled.Thus,an experimental study is conducted to reveal the fluid-structure interaction mechanism for a flexible plate ...In bio-inspired flapping-wing flight,lift generation and flexible deformation are intrinsically coupled.Thus,an experimental study is conducted to reveal the fluid-structure interaction mechanism for a flexible plate undergoing pitching and plunging motion,and theoretical models are proposed to predict either lift or deformation based on a series of simplifying assumptions.It is indicated that flexible plates can effectively reduce the amplitude of lift and pitching moment coefficients during dynamic stall,with increased flexibility leading to higher load reduction.To investigate the effect of plate flexibility on lift,a definition of effective angle of attack is proposed,incorporating the pitching and plunging motion and chordwise deformation of the flexible plate,which can reduce the hysteresis effect of the lift coefficient during dynamic stall.As a consequence,a theoretical model is developed to predict lift based on observed motion and deformation.On the other hand,another theoretical model is developed to predict flexible-plate deformation utilizing aerodynamic forces,revealing the effect of leading-edge vortex evolution on passive deformation.The influence of kinematic parameters,including the maximum effective angle of attack,reduced frequency,and Strouhal number,on the aerodynamic forces is further studied.Compared with the rigid plate,flexible plates exhibit lower sensitivity of aerodynamic forces to changes in kinematic parameters due to their inherent compliance and resulting deformation.The proposed theoretical models can serve as a reference for aerodynamic and deformation prediction in bio-inspired flexible structures.展开更多
We evaluated the performance of OpenFOAMGPT(GPT for generative pretrained transformers),which includes rating multiple large-language models.Some of the present models efficiently manage different computational fluid ...We evaluated the performance of OpenFOAMGPT(GPT for generative pretrained transformers),which includes rating multiple large-language models.Some of the present models efficiently manage different computational fluid dynamics(CFD)tasks,such as adjusting boundary conditions,turbulence models,and solver configurations,although their token cost and stability vary.Locally deployed smaller models such as the QwQ-32B(Q4 KM quantized model)struggled with generating valid solver files for complex processes.Zero-shot prompts commonly fail in simulations with intricate settings,even for large models.Challenges with boundary conditions and solver keywords stress the need for expert supervision,indicating that further development is needed to fully automate specialized CFD simulations.展开更多
We propose a suite of strategies for the parallel solution of fully implicit monolithic fluid-structure interaction(FSI).The solver is based on a modeling approach that uses the velocity and pressure as the primitive ...We propose a suite of strategies for the parallel solution of fully implicit monolithic fluid-structure interaction(FSI).The solver is based on a modeling approach that uses the velocity and pressure as the primitive variables,which offers a bridge between computational fluid dynamics(CFD)and computational structural dynamics.The spatiotemporal discretization leverages the variational multiscale formulation and the generalized-αmethod as a means of providing a robust discrete scheme.In particular,the time integration scheme does not suffer from the overshoot phenomenon and optimally dissipates high-frequency spurious modes in both subproblems of FSI.Based on the chosen fully implicit scheme,we systematically develop a combined suite of nonlinear and linear solver strategies.Invoking a block factorization of the Jacobian matrix,the Newton-Raphson procedure is reduced to solving two smaller linear systems in the multi-corrector stage.The first is of the elliptic type,indicating that the algebraic multigrid method serves as a well-suited option.The second exhibits a two-by-two block structure that is analogous to the system arising in CFD.Inspired by prior studies,the additive Schwarz domain decomposition method and the block-factorization-based preconditioners are invoked to address the linear problem.Since the number of unknowns matches in both subdomains,it is straightforward to balance loads when parallelizing the algorithm for distributed-memory architectures.We use two representative FSI benchmarks to demonstrate the robustness,efficiency,and scalability of the overall FSI solver framework.In particular,it is found that the developed FSI solver is comparable to the CFD solver in several aspects,including fixed-size and isogranular scalability as well as robustness.展开更多
In the present study,we concentrate on finding the dual solutions of biomagnetic fluid namely blood flow and heat transfer along with magnetic particles over a two dimensional shrinking cylinder in the presence of a m...In the present study,we concentrate on finding the dual solutions of biomagnetic fluid namely blood flow and heat transfer along with magnetic particles over a two dimensional shrinking cylinder in the presence of a magnetic dipole.To make the results physically realistic,stability analysis is also carried out in this study so that we realized which solution is stable and which is not.The governing partial equations are converted into ordinary differential equations by using similarity transformations and the numerical solution is calculated by applying bvp4c function technique in MATLAB software.The effects of different physical parameters are plotted graphically and discussed according to the outcomes of results.From the present study we observe that ferromagnetic interaction parameter had a great influenced on fluid velocity and temperature distributions.It is also found from the current analysis that the first and second solutions of shrinking cylinder obtained only when we applied particular ranges values of suction parameter.The most important characteristics part of study is to analyze the skin friction coefficient and rate of heat transfer which also covered in this analysis.It reveals that both skin friction coefficient and rate of heat transfer are reduced with rising values of ferromagnetic number.A comparison has also been made to make the solution feasible.展开更多
The present study investigates the dynamic behavior of a ternary-hybrid nanofluid within a tapered asymmetric channel,focusing on the impact of unsteady oscillatory flow under the influence of a magnetic field.This st...The present study investigates the dynamic behavior of a ternary-hybrid nanofluid within a tapered asymmetric channel,focusing on the impact of unsteady oscillatory flow under the influence of a magnetic field.This study addresses temperature-sensitive water transport mechanisms relevant to industrial applications such as thermal management and energy-efficient fluid transport.By suspending nanoparticles of diverse shapes-platelets,blades,and spheres in a hybrid base fluid comprising cobalt ferrite,magnesium oxide,and graphene oxide,the study examines the influence of both small and large volume fraction values.The governing equations are converted into a dimensionless form.With suitable assumptions,the partial differential equations(PDEs)are simplified into ordinary differential equations(ODEs),which are then solved using an analyticalmethod.Theproposed solution is verified using a numerical approach with the BVP4C solver.The analysis yields detailed graphs that depict the behavior of key fluid flow parameters,such as velocity,temperature,concentration,skin friction,Nusselt number,and Sherwood number,within the tapered asymmetric channel.展开更多
This study experimentally investigates complex wave structures and flow characteristics in a transonic free jet using two high-resolution optical diagnostics techniques:tomographic particle image velocimetry(Tomo-PIV)...This study experimentally investigates complex wave structures and flow characteristics in a transonic free jet using two high-resolution optical diagnostics techniques:tomographic particle image velocimetry(Tomo-PIV)and tomographic background oriented schlieren(Tomo-BOS).The measurements reveal three typical flow features in the jet:the potential core,shock cells,and shear layers.Notably,the shear layer displays significant velocity gradient variations across the lip line and plays a critical role in pressure regulation.The first invariant of the velocity gradient tensor,P,effectively characterizes local compressibility effects,facilitating the identification of key flow structures.In conjunction with-Q_(s)analysis,the results emphasize shear-driven deformation and the radial decay of wave intensity.Overall,the study demonstrates that current experimental techniques enable preliminary quantitative evaluation of transonic wave phenomena,providing valuable tools for the analysis of compressible flows.展开更多
The adjoint method is widely used in gradient-based optimization with high-dimensional design variables.However,the cost of solving the adjoint equations in each iteration is comparable to that of solving the flow fie...The adjoint method is widely used in gradient-based optimization with high-dimensional design variables.However,the cost of solving the adjoint equations in each iteration is comparable to that of solving the flow field,resulting in expensive computational costs.To improve the efficiency of solving adjoint equations,we propose a physics-constrained graph neural networks for solving adjoint equations,named ADJ-PCGN.ADJ-PCGN establishes a mapping relationship between flow characteristics and adjoint vector based on data,serving as a replacement for the computationally expensive numerical solution of adjoint equations.A physics-based graph structure and message-passing mechanism are designed to endow its strong fitting and generalization capabilities.Taking transonic drag reduction and maximum lift-drag ratio of the airfoil as examples,results indicate that ADJ-PCGN attains a similar optimal shape as the classical direct adjoint loop method.In addition,ADJ-PCGN demonstrates strong generalization capabilities across different mesh topologies,mesh densities,and out-of-distribution conditions.It holds the potential to become a universal model for aerodynamic shape optimization involving states,geometries,and meshes.展开更多
Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light in...Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light interference principle to measure the temporal variation of oil-film thickness caused by WSS,and calculates time-averaged WSS based on the variation of interference fringe width.However,small-scale noise,which is caused by defects on the target surface,ambient dust,and local oil-film non-uniformity,contaminates the interference fringe patterns and directly increases the measurement uncertainty.One practical way is to apply denoising methods to improve the accuracy of identifying the centroids of fringes.In the present study,quasi-bivariate variational mode decomposition(QBVMD)is proposed as a self-adaptive denoising method to remove small-scale noise.Since no characteristic information of fringe patterns is required in the QBVMD-based denoising method,it has higher accuracy and lower uncertainty than the conventional OFI denoising methods,which need to pre-set the mask signal or the bandpass frequency,i.e.,cross-correlation or spectral filtering.Thus,it facilitates the automatic identification of time-varying inhomogeneous fringes.Two sets of experiments,i.e.,WSS measurement on either a canonical flat-plate turbulent boundary layer(TBL)or a TBL perturbed by micro vortex generators(MVG),were conducted to validate the applicability of this QBVMD-OFI method.The former experiment shows that the accuracy of QBVMD-OFI is equivalent to near-wall high-resolution particle image velocimetry,and is considerably higher than that of a dual hot-film sensor.As for the latter,QBVMD-OFI provides sufficient spatial resolution to resolve fine WSS structures generated by MVG.展开更多
A constitutive equation theory of Oldroyd fluid B type,i.e.the co-rotational derivative type,is developed for the anisotropic-viscoelastic fluid of liquid crystalline(LC)polymer.Analyzing the influence of the orientat...A constitutive equation theory of Oldroyd fluid B type,i.e.the co-rotational derivative type,is developed for the anisotropic-viscoelastic fluid of liquid crystalline(LC)polymer.Analyzing the influence of the orientational motion on the material behavior and neglecting the influence,the constitutive equation is applied to a simple case for the hydrodynamic motion when the orientational contribution is neglected in it and the anisotropic relaxation,retardation times and anisotropic viscosi- ties are introduced to describe the macroscopic behavior of the anisotropic LC polymer fluid.Using the equation for the shear flow of LC polymer fluid,the analytical expressions of the apparent viscosity and the normal stress differences are given which are in a good agreement with the experimental results of Baek et al.For the fiber spinning flow of the fluid,the analytical expression of the extensional viscosity is given.展开更多
One of many interesting research activities in biofluidmechanics is dedicated to investigations of locomotion in water. Some of propulsion mechanisms observed in the underwater world are used in the development proces...One of many interesting research activities in biofluidmechanics is dedicated to investigations of locomotion in water. Some of propulsion mechanisms observed in the underwater world are used in the development process of underwater autonomic vehicles （AUV）. In order to characterise several solutions according to their manoeuvrability, influence on the surrounding fluid and energetic efficiency, a detailed analysis of fin-like movement is indispensable. In the current paper an analysis of undulatory, oscillatory and combined fin-like movements by means of numerical simulation is carried out. The conservation equation of mass and the conservation equation of momentum axe solved with the Finite Volume Method （FWM） by use of the software CFX-10.0. The undulatory and oscillatory fin movements axe modelled with an equation that is implemented within an additional subroutine and joined with the main solver. N carried out in the computational domain, in which one fin is fixed in a flow-through water duct. Simulations axe carded out in the range of the Re number up to 105. The results show significant influence of applied fin motion on the velocity distribution in the surrounding fluid.展开更多
Applicable in fluid dynamics and plasmas, a generalized variable-coefficient Korteweg-de Vries （vcKdV） model is investigated. The bilinear form and analytic N-soliton-like solution for such a model are derived by th...Applicable in fluid dynamics and plasmas, a generalized variable-coefficient Korteweg-de Vries （vcKdV） model is investigated. The bilinear form and analytic N-soliton-like solution for such a model are derived by the Hirota method and Wronskian technique. Additionally, the bilinear auto-Bǎcklund transformation between （N-1）- soliton-like and N-soliton-like solutions is verified.展开更多
Ferrofluid moving thin films and their possible significance with regard to active flow control for lift and attack angle enhancement are discussed.In this strategy,a very thin film of ferrofluid is strongly attached ...Ferrofluid moving thin films and their possible significance with regard to active flow control for lift and attack angle enhancement are discussed.In this strategy,a very thin film of ferrofluid is strongly attached at the wall of the wing by a normal magnetic field from below and pumped tangentially along the wing.Utilizing a simplified physical model and from the available experimental data on moving walls,the expected lift enhancement and effect on the attack angle were assessed.Additional research and design is required in order to explore the possibilities in the use of ferrofluid moving thin films.展开更多
Thrust vectoring technology plays an important role in improving the maneuverability of aircraft.In order to overcome the disadvantages of mechanical thrust vectoring nozzles,such as complications of structure and sig...Thrust vectoring technology plays an important role in improving the maneuverability of aircraft.In order to overcome the disadvantages of mechanical thrust vectoring nozzles,such as complications of structure and significant increases in weight and cost,fluidic thrust vectoring noz-zles are proposed.Dual Throat fluidic thrust vectoring Nozzle(DTN)has received wide attention due to its excellent thrust vectoring efficiency and minimal thrust loss.In this study,three-dimensional unsteady numerical simulations of a single axisymmetric DTN are conducted first to analyze its dynamic response.Then the pitch and yaw control characteristics of DTN equipped on a flying-wing aircraft are investigated.It is found that the dynamic response will experience three stages:rapid-deflecting stage,oscillating stage,and steady stage.A complete recirculation zone forms at the end of the rapid-deflecting stage,which pushes the primary flow to attach to the wall opposite the secondary injection.Meanwhile,the exhaust flow is deflected.In terms of DTN's appli-cation,the DTN equipped on the flying-wing aircraft is capable of providing effective pitch and yaw moments at all angles of attack and Mach numbers.In addition,continuous pitch and yaw moments can be obtained by adjusting the secondary mass flow ratios.The control moment is gen-erated due to the asymmetrical pressure distribution of nozzle surface,which is mainly contributed by the pressure decrease on the secondary injection surface.Moreover,the DTN equipped on the flying-wing aircraft has a relatively high thrust vectoring efficiency of around 5°/%and a thrust coefficient of around 0.95 when nozzle pressure ratio equals 4.These results provide an important theoretical basis for the practical application of DTN.展开更多
Employing the method which can be used to demonstrate the infinite conservation laws for the standard Kortewegde Vries （KdV） equation, we prove that the variable-coeFficient KdV equation under the Painlevé test...Employing the method which can be used to demonstrate the infinite conservation laws for the standard Kortewegde Vries （KdV） equation, we prove that the variable-coeFficient KdV equation under the Painlevé test condition also possesses the formal conservation laws.展开更多
A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary c...A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.展开更多
基金the National Natural Science Foundation of China under Grant No.11772017the Fundamental Research Funds for the Central Universities
文摘In this paper,we investigate a(2+1)-dimensional variable-coefficient modified dispersive waterwave system in fluid mechanics.We prove the Painlevéintegrability for that system via the Painlevéanalysis.We find some auto-B?cklund transformations for that system via the truncated Painlevéexpansions.Bilinear forms and N-soliton solutions are constructed,where N is a positive integer.We discuss the inelastic interactions,elastic interactions and soliton resonances for the two solitons.We also graphically demonstrate that the velocities of the solitons are affected by the variable coefficient of that system.
基金Supported by the National Natural Science Foundation of China under Grant No.60772023the Open Fund under Grant No.SKLSDE-2011KF-03+2 种基金Supported project under Grant No.SKLSDE-2010ZX-07 of the State Key Laboratory of Software Development Environment,Beijing University of Aeronautics and Astronauticsthe National High Technology Research and Development Program of China(863 Program) under Grant No.2009AA043303the Specialized Research Fund for the Doctoral Program of Higher Education under Grant No.200800130006,Chinese Ministry of Education
文摘This paper is to investigate the extended(2+1)-dimensional Konopelchenko-Dubrovsky equations,which can be applied to describing certain phenomena in the stratified shear flow,the internal and shallow-water waves, plasmas and other fields.Painleve analysis is passed through via symbolic computation.Bilinear-form equations are constructed and soliton solutions are derived.Soliton solutions and interactions are illustrated.Bilinear-form Backlund transformation and a type of solutions are obtained.
基金Supported by the State Key Laboratory of Software Development Environment under Grant No.SKLSDE-2012ZX-10,Beijing University of Aeronautics and Astronauticsthe Fundamental Research Funds for the Central Universities of China under Grant No.2011BUPTYB02+2 种基金the Open Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications)the Specialized Research Fund for the Doctoral Program of Higher Education (No. 200800130006),Chinese Ministry of Educationthe Scientific Research Common Program of Beijing Municipal Commission of Education under Grant No. KM201010772020
文摘Burgers-type equations can describe some phenomena in fluids,plasmas,gas dynamics,traffic,etc.In this paper,an integrable hierarchy covering the lattice Burgers equation is derived from a discrete spectral problem.N-fold Darboux transformation(DT) and conservation laws for the lattice Burgers equation are constructed based on its Lax pair.N-soliton solutions in the form of Vandermonde-like determinant are derived via the resulting DT with symbolic computation,structures of which are shown graphically.Coexistence of the elastic-inelastic interaction among the three solitons is firstly reported for the lattice Burgers equation,even if the similar phenomenon for certern continuous systems is known.Results in this paper might be helpful for understanding some ecological problems describing the evolution of competing species and the propagation of nonlinear waves in fluids.
基金Supported by the National Natural Science Foundation of China under Grant No. 60772023by the Open Fund of the State Key Laboratory of Software Development Environment under Grant No. BUAA-SKLSDE-09KF-04+1 种基金Beijing University of Aeronautics and Astronautics, by the National Basic Research Program of China (973 Program) under Grant No. 2005CB321901by the Specialized Research Fund for the Doctoral Program of Higher Education under Grant Nos. 20060006024 and 200800130006, Chinese Ministry of Education
文摘This paper is to investigate a variable-coefficient modified Kortweg-de Vries （vc-mKdV） model, which describes some situations from fluid mechanics, ocean dynamics, and plasma mechanics. By the AblowRz-Kaup-NewellSegur procedure and symbolic computation, the Lax pair of the vc-MKdV model is derived. Then, based on the aforementioned Lax pair, the Darboux transformation is constructed and a new one-soliton-like solution is obtained as weft Features of the one-soliton-like solution are analyzed and graphically discussed to illustrate the influence of the variable coefficients in the solitonlike propagation.
基金Supported by the National Natural Science Foundation of China under Grant No.11272023the Open Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications)by the Fundamental Research Funds for the Central Universities of China under Grant No.2011BUPTYB02
文摘The Korteweg-de Vries(Kd V)-type equations have been seen in fluid mechanics,plasma physics and lattice dynamics,etc. This paper will address the bilinearization problem for some higher-order Kd V equations. Based on the relationship between the bilinear method and Bell-polynomial scheme,with introducing an auxiliary independent variable,we will present the general bilinear forms. By virtue of the symbolic computation,one-and two-soliton solutions are derived.
基金supported by the National Natural Science Foundation of China(Grant No.12472279)。
文摘In bio-inspired flapping-wing flight,lift generation and flexible deformation are intrinsically coupled.Thus,an experimental study is conducted to reveal the fluid-structure interaction mechanism for a flexible plate undergoing pitching and plunging motion,and theoretical models are proposed to predict either lift or deformation based on a series of simplifying assumptions.It is indicated that flexible plates can effectively reduce the amplitude of lift and pitching moment coefficients during dynamic stall,with increased flexibility leading to higher load reduction.To investigate the effect of plate flexibility on lift,a definition of effective angle of attack is proposed,incorporating the pitching and plunging motion and chordwise deformation of the flexible plate,which can reduce the hysteresis effect of the lift coefficient during dynamic stall.As a consequence,a theoretical model is developed to predict lift based on observed motion and deformation.On the other hand,another theoretical model is developed to predict flexible-plate deformation utilizing aerodynamic forces,revealing the effect of leading-edge vortex evolution on passive deformation.The influence of kinematic parameters,including the maximum effective angle of attack,reduced frequency,and Strouhal number,on the aerodynamic forces is further studied.Compared with the rigid plate,flexible plates exhibit lower sensitivity of aerodynamic forces to changes in kinematic parameters due to their inherent compliance and resulting deformation.The proposed theoretical models can serve as a reference for aerodynamic and deformation prediction in bio-inspired flexible structures.
基金supported by the Royal Society(Grant No.RG\R1\251236)the Fundamental Research Funds for the Central Universities of China(Grant No.JKF-2025055317102).
文摘We evaluated the performance of OpenFOAMGPT(GPT for generative pretrained transformers),which includes rating multiple large-language models.Some of the present models efficiently manage different computational fluid dynamics(CFD)tasks,such as adjusting boundary conditions,turbulence models,and solver configurations,although their token cost and stability vary.Locally deployed smaller models such as the QwQ-32B(Q4 KM quantized model)struggled with generating valid solver files for complex processes.Zero-shot prompts commonly fail in simulations with intricate settings,even for large models.Challenges with boundary conditions and solver keywords stress the need for expert supervision,indicating that further development is needed to fully automate specialized CFD simulations.
基金This work was supported by the National Natural Science Foundation of China(Grant No.12172160)Shenzhen Science and Technology Program(Grant No.JCYJ20220818100600002)+1 种基金South-ern University of Science and Technology(Grant No.Y01326127)the Department of Science and Technology of Guangdong Province(Grant Nos.2020B1212030001 and 2021QN020642).
文摘We propose a suite of strategies for the parallel solution of fully implicit monolithic fluid-structure interaction(FSI).The solver is based on a modeling approach that uses the velocity and pressure as the primitive variables,which offers a bridge between computational fluid dynamics(CFD)and computational structural dynamics.The spatiotemporal discretization leverages the variational multiscale formulation and the generalized-αmethod as a means of providing a robust discrete scheme.In particular,the time integration scheme does not suffer from the overshoot phenomenon and optimally dissipates high-frequency spurious modes in both subproblems of FSI.Based on the chosen fully implicit scheme,we systematically develop a combined suite of nonlinear and linear solver strategies.Invoking a block factorization of the Jacobian matrix,the Newton-Raphson procedure is reduced to solving two smaller linear systems in the multi-corrector stage.The first is of the elliptic type,indicating that the algebraic multigrid method serves as a well-suited option.The second exhibits a two-by-two block structure that is analogous to the system arising in CFD.Inspired by prior studies,the additive Schwarz domain decomposition method and the block-factorization-based preconditioners are invoked to address the linear problem.Since the number of unknowns matches in both subdomains,it is straightforward to balance loads when parallelizing the algorithm for distributed-memory architectures.We use two representative FSI benchmarks to demonstrate the robustness,efficiency,and scalability of the overall FSI solver framework.In particular,it is found that the developed FSI solver is comparable to the CFD solver in several aspects,including fixed-size and isogranular scalability as well as robustness.
文摘In the present study,we concentrate on finding the dual solutions of biomagnetic fluid namely blood flow and heat transfer along with magnetic particles over a two dimensional shrinking cylinder in the presence of a magnetic dipole.To make the results physically realistic,stability analysis is also carried out in this study so that we realized which solution is stable and which is not.The governing partial equations are converted into ordinary differential equations by using similarity transformations and the numerical solution is calculated by applying bvp4c function technique in MATLAB software.The effects of different physical parameters are plotted graphically and discussed according to the outcomes of results.From the present study we observe that ferromagnetic interaction parameter had a great influenced on fluid velocity and temperature distributions.It is also found from the current analysis that the first and second solutions of shrinking cylinder obtained only when we applied particular ranges values of suction parameter.The most important characteristics part of study is to analyze the skin friction coefficient and rate of heat transfer which also covered in this analysis.It reveals that both skin friction coefficient and rate of heat transfer are reduced with rising values of ferromagnetic number.A comparison has also been made to make the solution feasible.
基金supported by the Government of the Basque Country,programs:Elkartek Grant No.DBaskIN ELKARTEK 25/28 and Grant No.:KK-2024/00035 and ITSAS-REM Grant No.:IT1514-22 funded by the High-Level Talent Research Start-up Project Funding of Henan Academy of Sciences(Project No.241819246).
文摘The present study investigates the dynamic behavior of a ternary-hybrid nanofluid within a tapered asymmetric channel,focusing on the impact of unsteady oscillatory flow under the influence of a magnetic field.This study addresses temperature-sensitive water transport mechanisms relevant to industrial applications such as thermal management and energy-efficient fluid transport.By suspending nanoparticles of diverse shapes-platelets,blades,and spheres in a hybrid base fluid comprising cobalt ferrite,magnesium oxide,and graphene oxide,the study examines the influence of both small and large volume fraction values.The governing equations are converted into a dimensionless form.With suitable assumptions,the partial differential equations(PDEs)are simplified into ordinary differential equations(ODEs),which are then solved using an analyticalmethod.Theproposed solution is verified using a numerical approach with the BVP4C solver.The analysis yields detailed graphs that depict the behavior of key fluid flow parameters,such as velocity,temperature,concentration,skin friction,Nusselt number,and Sherwood number,within the tapered asymmetric channel.
文摘This study experimentally investigates complex wave structures and flow characteristics in a transonic free jet using two high-resolution optical diagnostics techniques:tomographic particle image velocimetry(Tomo-PIV)and tomographic background oriented schlieren(Tomo-BOS).The measurements reveal three typical flow features in the jet:the potential core,shock cells,and shear layers.Notably,the shear layer displays significant velocity gradient variations across the lip line and plays a critical role in pressure regulation.The first invariant of the velocity gradient tensor,P,effectively characterizes local compressibility effects,facilitating the identification of key flow structures.In conjunction with-Q_(s)analysis,the results emphasize shear-driven deformation and the radial decay of wave intensity.Overall,the study demonstrates that current experimental techniques enable preliminary quantitative evaluation of transonic wave phenomena,providing valuable tools for the analysis of compressible flows.
基金supported by the National Natural Science Foundation of China(Grant No.12272316).
文摘The adjoint method is widely used in gradient-based optimization with high-dimensional design variables.However,the cost of solving the adjoint equations in each iteration is comparable to that of solving the flow field,resulting in expensive computational costs.To improve the efficiency of solving adjoint equations,we propose a physics-constrained graph neural networks for solving adjoint equations,named ADJ-PCGN.ADJ-PCGN establishes a mapping relationship between flow characteristics and adjoint vector based on data,serving as a replacement for the computationally expensive numerical solution of adjoint equations.A physics-based graph structure and message-passing mechanism are designed to endow its strong fitting and generalization capabilities.Taking transonic drag reduction and maximum lift-drag ratio of the airfoil as examples,results indicate that ADJ-PCGN attains a similar optimal shape as the classical direct adjoint loop method.In addition,ADJ-PCGN demonstrates strong generalization capabilities across different mesh topologies,mesh densities,and out-of-distribution conditions.It holds the potential to become a universal model for aerodynamic shape optimization involving states,geometries,and meshes.
文摘Characterized by high accuracy and operational simplicity,oil-film interferometry(OFI)has served as an effective wall-shear stress(WSS)measurement technique over the past decades.It utilizes the monochromatic light interference principle to measure the temporal variation of oil-film thickness caused by WSS,and calculates time-averaged WSS based on the variation of interference fringe width.However,small-scale noise,which is caused by defects on the target surface,ambient dust,and local oil-film non-uniformity,contaminates the interference fringe patterns and directly increases the measurement uncertainty.One practical way is to apply denoising methods to improve the accuracy of identifying the centroids of fringes.In the present study,quasi-bivariate variational mode decomposition(QBVMD)is proposed as a self-adaptive denoising method to remove small-scale noise.Since no characteristic information of fringe patterns is required in the QBVMD-based denoising method,it has higher accuracy and lower uncertainty than the conventional OFI denoising methods,which need to pre-set the mask signal or the bandpass frequency,i.e.,cross-correlation or spectral filtering.Thus,it facilitates the automatic identification of time-varying inhomogeneous fringes.Two sets of experiments,i.e.,WSS measurement on either a canonical flat-plate turbulent boundary layer(TBL)or a TBL perturbed by micro vortex generators(MVG),were conducted to validate the applicability of this QBVMD-OFI method.The former experiment shows that the accuracy of QBVMD-OFI is equivalent to near-wall high-resolution particle image velocimetry,and is considerably higher than that of a dual hot-film sensor.As for the latter,QBVMD-OFI provides sufficient spatial resolution to resolve fine WSS structures generated by MVG.
基金The project supported by the National Natural Science Foundation of China(19832050 and 10372100)
文摘A constitutive equation theory of Oldroyd fluid B type,i.e.the co-rotational derivative type,is developed for the anisotropic-viscoelastic fluid of liquid crystalline(LC)polymer.Analyzing the influence of the orientational motion on the material behavior and neglecting the influence,the constitutive equation is applied to a simple case for the hydrodynamic motion when the orientational contribution is neglected in it and the anisotropic relaxation,retardation times and anisotropic viscosi- ties are introduced to describe the macroscopic behavior of the anisotropic LC polymer fluid.Using the equation for the shear flow of LC polymer fluid,the analytical expressions of the apparent viscosity and the normal stress differences are given which are in a good agreement with the experimental results of Baek et al.For the fiber spinning flow of the fluid,the analytical expression of the extensional viscosity is given.
文摘One of many interesting research activities in biofluidmechanics is dedicated to investigations of locomotion in water. Some of propulsion mechanisms observed in the underwater world are used in the development process of underwater autonomic vehicles （AUV）. In order to characterise several solutions according to their manoeuvrability, influence on the surrounding fluid and energetic efficiency, a detailed analysis of fin-like movement is indispensable. In the current paper an analysis of undulatory, oscillatory and combined fin-like movements by means of numerical simulation is carried out. The conservation equation of mass and the conservation equation of momentum axe solved with the Finite Volume Method （FWM） by use of the software CFX-10.0. The undulatory and oscillatory fin movements axe modelled with an equation that is implemented within an additional subroutine and joined with the main solver. N carried out in the computational domain, in which one fin is fixed in a flow-through water duct. Simulations axe carded out in the range of the Re number up to 105. The results show significant influence of applied fin motion on the velocity distribution in the surrounding fluid.
基金Supported by the Key Project of the Ministry of Education of China under Grant No 106033, and the National Natural Science Foundation of China under Grant Nos 60372095 and 10272017, the Green Path Programme of Air Force of the Chinese People＇s Liberation Army, the Cheung Kong Scholars Programme of the Ministry of Education of China, and Li Ka Shing Foundation of Hong Kong.
文摘Applicable in fluid dynamics and plasmas, a generalized variable-coefficient Korteweg-de Vries （vcKdV） model is investigated. The bilinear form and analytic N-soliton-like solution for such a model are derived by the Hirota method and Wronskian technique. Additionally, the bilinear auto-Bǎcklund transformation between （N-1）- soliton-like and N-soliton-like solutions is verified.
基金supported by the Spanish Ministry of Economy and Competitiveness under Fellowship Grant Ramon y Cajal(No.RYC-2013-13459)。
文摘Ferrofluid moving thin films and their possible significance with regard to active flow control for lift and attack angle enhancement are discussed.In this strategy,a very thin film of ferrofluid is strongly attached at the wall of the wing by a normal magnetic field from below and pumped tangentially along the wing.Utilizing a simplified physical model and from the available experimental data on moving walls,the expected lift enhancement and effect on the attack angle were assessed.Additional research and design is required in order to explore the possibilities in the use of ferrofluid moving thin films.
基金supported by the National Natural Science Foundation of China (Nos.U2141253 and 11721202).
文摘Thrust vectoring technology plays an important role in improving the maneuverability of aircraft.In order to overcome the disadvantages of mechanical thrust vectoring nozzles,such as complications of structure and significant increases in weight and cost,fluidic thrust vectoring noz-zles are proposed.Dual Throat fluidic thrust vectoring Nozzle(DTN)has received wide attention due to its excellent thrust vectoring efficiency and minimal thrust loss.In this study,three-dimensional unsteady numerical simulations of a single axisymmetric DTN are conducted first to analyze its dynamic response.Then the pitch and yaw control characteristics of DTN equipped on a flying-wing aircraft are investigated.It is found that the dynamic response will experience three stages:rapid-deflecting stage,oscillating stage,and steady stage.A complete recirculation zone forms at the end of the rapid-deflecting stage,which pushes the primary flow to attach to the wall opposite the secondary injection.Meanwhile,the exhaust flow is deflected.In terms of DTN's appli-cation,the DTN equipped on the flying-wing aircraft is capable of providing effective pitch and yaw moments at all angles of attack and Mach numbers.In addition,continuous pitch and yaw moments can be obtained by adjusting the secondary mass flow ratios.The control moment is gen-erated due to the asymmetrical pressure distribution of nozzle surface,which is mainly contributed by the pressure decrease on the secondary injection surface.Moreover,the DTN equipped on the flying-wing aircraft has a relatively high thrust vectoring efficiency of around 5°/%and a thrust coefficient of around 0.95 when nozzle pressure ratio equals 4.These results provide an important theoretical basis for the practical application of DTN.
基金Supported by the Key Project of Chinese Ministry of Education under Grant No 106033, the National Natural Science Foundation of China under Grant Nos 60372095 and 60772023, Open Fund of the State Key Laboratory of Software Development Environment under Grant No SKLSDE-07-001, Beijing University of Aeronautics and Astronautics, the National Basic Research Programme of China under Grant No 2005CB321901, the Green Path Programme of Air Force of the Chinese People＇s Liberation Army, the Cheung Kong Scholars Programme of the Ministry of Education of China and Li Ka Shing Foundation of Hong Kong.
文摘Employing the method which can be used to demonstrate the infinite conservation laws for the standard Kortewegde Vries （KdV） equation, we prove that the variable-coeFficient KdV equation under the Painlevé test condition also possesses the formal conservation laws.
文摘A Jeffery-Hamel （J-H） flow model of the non-Newtonian fluid type inside a convergent wedge （inclined walls） with a wall friction is derived by a nonlinear ordinary differential equation with appropriate boundary conditions based on similarity relationships. Unlike the usual power law model, this paper develops nonlinear viscosity based only on a tangential coordinate function due to the radial geometry shape. Two kinds of solutions are developed, i.e., analytical and semi-analytical （numerical） solutions with suitable assumptions. As a result of the parametric examination, it has been found that the Newtonian normalized velocity gradually decreases with the tangential direction progress. Also, an increase in the friction coefficient leads to a decrease in the normalized Newtonian velocity profile values. However, an increase in the Reynolds number causes an increase in the normalized velocity function values. Additionally, for the small values of wedge semi-angle, the present solutions are in good agreement with the previous results in the literature.
