Flowfield inverse design can obtain the desired flow and contour with high design efficiency,short design cycle,and small modification need.In this study,the Euler equations are formulated in the stream-function coord...Flowfield inverse design can obtain the desired flow and contour with high design efficiency,short design cycle,and small modification need.In this study,the Euler equations are formulated in the stream-function coordinates and combined with the given boundary conditions to derive a gridless space-marching method for the inverse design of subsonic,transonic,and supersonic flowfields.Designers can prescribe the flow parameters along the reference streamline to design flowfields and aerodynamic contours.The method is validated by the theoretical transonic solution,computational fluid dynamics,and experimental data,respectively.The method supports the fabrication of a Mach 2.0 single expansion tunnel.The calibration data agree well with the prescribed pressure distribution.The method is successfully applied to inverse design of contractions,nozzles,and asymmetric channels.Compared to classical analytic contractions,the contractions designed by the space-marching method provide a more accurate transonic flow.Compared to the classical Sivells’nozzle,the nozzle designed by the space-marching method provides a smaller workload,a more flexible velocity distribution,a 20%reduction in length,and an equally uniform flow.Additionally,the space-marching method is applied to design the asymmetric channels under various Mach numbers.These asymmetric channels perfectly eliminate Mach waves,achieving the shock-free flow turning and high flow uniformity.These results validate the feasibility of the space-marching method,making it a good candidate for the inverse design of subsonic,transonic,and supersonic internal flowfields and aerodynamic contours.展开更多
Distributed ducted propellers hold significant promise for propulsion systems in Advanced Air Mobility(AAM) due to their high efficiency, low noise, and enhanced redundancy and safety. However, a standardized benchmar...Distributed ducted propellers hold significant promise for propulsion systems in Advanced Air Mobility(AAM) due to their high efficiency, low noise, and enhanced redundancy and safety. However, a standardized benchmark for comparing the aerodynamic characteristics of different ducted propeller configurations remains lacking. Including additional ducted propellers can further complicate the flow field. This paper proposes an equivalent design method for ducted propellers based on the momentum theorem and similarity criteria, introducing three equivalent ducted propeller cases. Transient numerical simulations are conducted using the sliding mesh model. The three cases produce comparable thrust while consuming the same power, with the volume of distributed ducted propellers being reduced by over 29% compared to the single ducted propeller. This study investigates the effect of rotational frequency on aerodynamic performance under hovering conditions. While propeller performance demonstrates low sensitivity to variations in rotational frequency, duct performance exhibits high sensitivity. The research further examines how rotational frequency changes the pressure difference between the duct leading edge and trailing edge. Based on a sensitivity analysis of aerodynamic performance, the flow field mechanisms under different rotational consistency are examined for the case with one duct and two propellers. Differences in aerodynamic performance are attributed to the airflow velocity gradient differences at the duct leading edge and the flow separation characteristics on the crossing side. These findings are significant for enhancing the performance of distributed ducted propellers and improving aircraft controllability.展开更多
This paper focuses on the optimization of the outlet temperature field of a hydrogen micromixing diffusion combustor for a micro-turbojet engine with a thrust of 20kgf.The joint simulation optimization platform was es...This paper focuses on the optimization of the outlet temperature field of a hydrogen micromixing diffusion combustor for a micro-turbojet engine with a thrust of 20kgf.The joint simulation optimization platform was established combiningWorkbench and UG and the multi-parameter driven optimization design process was developed.The surrogate models and genetic algorithms were employed to investigate the influences of key parameters on the hotspot temperature at the combustor exit.It was found that smaller diameters of the dilution holes and positions further from the exit lead to lower hotspot temperatures.Additionally,an optimal solution for achieving a uniform temperature distribution at the combustor outlet was obtained.This solution involves a single row of dilution holes on both the inner and outer walls of the flame tube,arranged in an alternating axial and angular pattern.Through aerothermal process analysis,it was determined that the outlet temperature distribution coefficient(OTDF)of the combustion chamber is below 0.2.Meanwhile,the axial dimension of the flame is short,approximately one-third of the flame tube length.The conclusions derived from this study provide important guidance for the design of hydrogen micromix diffusion combustor.展开更多
In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver- sion mode, a virtual blade model （VBM） and an real blade model （RBM） are established respec- tively. A new multi-layer mo...In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver- sion mode, a virtual blade model （VBM） and an real blade model （RBM） are established respec- tively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map （AIM） is established to search corresponding donor elements in the present moving- embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data （SPMD） model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum- Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are val- idated by comparing the calculated results with available experimental data. Then, unsteady aero- dynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles （15°, 30°, 60°） and a whole conversion mode which converses from 0° to 90°, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these investigation results could provide a good foundation for tilt-rotor aircraft design in the future.展开更多
This paper studies numerically the influence of the tip clearance on the three dimensional viscous flowfield and performance of the NASA Low Speed Centrifugal Compressor (LSCC) impeller with a vaneless diffuser A thre...This paper studies numerically the influence of the tip clearance on the three dimensional viscous flowfield and performance of the NASA Low Speed Centrifugal Compressor (LSCC) impeller with a vaneless diffuser A three dimensional viscous code developed by the authors is applied with several acceleration methods: local time step, multigrid and residual smoothing The computations were performed under several operating conditions with four different tip clearance sizes(0 0%,50%,100% and 200% design t...展开更多
In the commercial utilization of rigid ceramic filters, the performance of pulse cleaning has crucial effects on the long-term stable operation. In order to get a clear insight into the nature of this cleaning process...In the commercial utilization of rigid ceramic filters, the performance of pulse cleaning has crucial effects on the long-term stable operation. In order to get a clear insight into the nature of this cleaning process and provide a solid basis for industrial applications, the flow in ceramic candle filter was investigated. The flow in the pulse-jetspace and inside the ceramic candle is regarded as two- dimensional, unsteady, compressible flow, and numerical simulation is carried out by computational fluid dynamics. The numerical predictions of flow field are in good agreement with the experimental measurements. Effects of the candle diameter, the separation distance between the nozzle and the candle injector and the length of the candle on the flowfield have been numerically analyzed to provide the basis for the optimum design of the pulse cleaning system.展开更多
In this work,the flow fields in three-dimensional(3D)sidewall compression inlets are investigated theoretically and numerically.Combining spatial dimension reduction theory with the shock dynamics theory,a detailed an...In this work,the flow fields in three-dimensional(3D)sidewall compression inlets are investigated theoretically and numerically.Combining spatial dimension reduction theory with the shock dynamics theory,a detailed analysis of the flowfield in the compression part of an inlet is proposed.Using this analytical approach,wave configurations are determined and flowfield parameters are solved;numerical simulations are conducted to validate these theoretical results.The effects of the attack angle and yaw angle on the pressure ratio,wave structures,and total pressure recovery performance are discussed in detail.Findings offer an effective way to study shock/shock interaction(SSI)in sidewall inlets,which is essential to the designing of such inlets.展开更多
To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models...To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.展开更多
Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-mo...Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics （CFD） method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and volume of fluid （VOF） model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function （UDF） based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environnaent.展开更多
Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of...Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of a rotating slanted hotwire is introduced to measure the stator outlet three-dimensional flow field.The procedure for solving the mean three-dimensional velocity component involving the least-squares technique can be accomplished via the LSQNONLIN optimization function of Matlab.Under different work conditions,the stator outlet secondary flow is more intense at higher inlet flux.Moreover,the shortest stator height will lead to the most intense secondary flow,which gains the largest axial velocity component(w) and radial velocity component (u),but the smallest circumferential velocity component(v).展开更多
Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field.Due to the extremely difficult experiment,limited wind-tunnel conditions and high cost,most problems in rarefied flow r...Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field.Due to the extremely difficult experiment,limited wind-tunnel conditions and high cost,most problems in rarefied flow regime are investigated through numerical methods,in which the direct simulation Monte-Carlo(DSMC)method is widely adopted.And the unstructured DSMC method is employed here.Flows around a vertical plate at a given velocity 7 500 m/s are simulated.For gas rarefaction is judged by the free-stream Knudsen number(Kn),two vital factors are considered:molecular number density and the plate′s length.Cases in which Kn varies from 0.035 to13.36 are simulated.Flow characters in the whole rarefied regime are described,and flow-field structure affected by Knis analyzed.Then,the dimensionless position D*of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation.Through flow-field tracing and least-square numerical method analyzing,it is proved that hypersonic rarefied flow field expands outward linearly with the increase of 1/2Kn.An empirical method is proposed,which can be used for the prediction of the hypersonic flow-field structure at a given inflow velocity,especially the shock wave position.展开更多
The structure of inert turbulent flows, stabilized in a Bluff-Body burner, is studied considering different volumetric flows for Nitrogen jet and annular air in coflow configuration. Flowfield analysis on Bluff-Body b...The structure of inert turbulent flows, stabilized in a Bluff-Body burner, is studied considering different volumetric flows for Nitrogen jet and annular air in coflow configuration. Flowfield analysis on Bluff-Body burner is essential to improve the knowledge about this burner, which plays an important role in industrial applications. Thus, vector velocity field is performed, employing Particle Image Velocimetry technique. Also, an uncertainty analysis is performed considering parameters involved in this technique yielding 6% to velocity measurements. The acquired information produces the results based in flowfield structure, which are presented in terms of statistical momentum and Reynolds stress, in which Boussinesq Hypothesis is considered to incompressible flows. However, this hypothesis fails in certain conditions. In this way, is possible to comprehend and provide experimental data from the turbulent effects on the flowfield and also contribute to predict the combustion flows, in order to enable the validation and develop numerical models.展开更多
High-pressure shallow(gas/water)flow is often hidden in the deepwater seabed,so penetrating shallowflow in drilling without BOP will be highly risky.In this case,the conventional well killing method to balance the for...High-pressure shallow(gas/water)flow is often hidden in the deepwater seabed,so penetrating shallowflow in drilling without BOP will be highly risky.In this case,the conventional well killing method to balance the formation pressure with back pressure generated by well head equipment is no longer suitable.Based on the analysis of structural characteristics of domestic and foreign multi-phase mixing systems,a ZM-2 drillingfluid density adjustment mixing device with independent intellectual property right was developed according to the principles of dy-namic well killing.The device is mainly composed of a throttle valve,a high-precision electromagneticflowmeter,a mixer,dumbbell-shaped nozzles,connecting pipes and other components.Fixed on the mixer are three inlets tofill heavy mud,seawater and additives.Opposed jetting is adopted to realize rapid and uniform mixing offluids with different densities.A laboratory test was conducted to work out the relationship between throttle opening and injectionflow rate and establish a linear relationship between killingfluid density and heavy mudflow.The results offield test conducted in the Nanhai No.8 drill ship showed that the mixing device was stable in operation and excellent in mixing performance.The density difference of ingredient mixture could be controlled within 0.05 g/cm3 after the mixtureflowed out of the mixing chamber of the mixer of about 0.3 m long,so such high precision can meet the requirement of dynamic well killing.展开更多
Accurate acquisition of the distribution offlow parameters inside the supersonic combustor is of great significance for hypersonicflight control.It is an interesting attempt to introduce a data-driven model to a super...Accurate acquisition of the distribution offlow parameters inside the supersonic combustor is of great significance for hypersonicflight control.It is an interesting attempt to introduce a data-driven model to a supersonic combustor forflowfield prediction.This paper proposes a novel method for predicting theflowfield in a dual-mode combustor.Aflowfield prediction convolutional neural network with multiple branches is built.Numerical investiga-tions for a strut variable geometry combustor have been conducted to obtainflowfield data for training the network as aflowfield prediction model.Richflowfield data are obtained by changing the equivalent ratio,incomingflow condition and geometry of the supersonic combustor.The Mach number distribution can be obtained from the trainedflowfield prediction model using the combustor wall pressure as input with high accuracy.The accuracy offlowfield prediction is discussed in several aspects.Further,the combustion mode detection is im-plemented on the predictionflowfield.展开更多
A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce tim...A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce time cost,and a combination of the mass flow balance technique and the axisymmetric analog is proposed to account for the entropy swallowing effects.A three-dimensional linear method is derived to fit the vehicle surface flowfields.Then a new axisymmetric analog method based on linear flowfields and linear surface equations is developed,with the complexity and computational cost reduced dramatically.In the stagnation region,an implicit surface fitting is introduced to approximate the primary curvatures and a robust aeroheating prediction method is constructed.The proposed approach is verified on a variety of configurations including spherically blunted cone,double ellipsoid and aerospace vehicle.Numerical results indicate the followings:1)The approach predicts aeroheating in about one second and the results agree well with CFD simulations and wind-tunnel measurements;2)with the help of entropy correction,the precision is further improved in the streamline diverging regions on the vehicle surface,while little improvement is found after entropy correction in the regions where the streamlines do not diverge.展开更多
A numerical simulation method for parachute Fluid-Structure Interaction （FSI） problem using Semi-Implicit Method for Pres- sure-Linked Equations （SIMPLE） algorithm is proposed. This method could be used in both co...A numerical simulation method for parachute Fluid-Structure Interaction （FSI） problem using Semi-Implicit Method for Pres- sure-Linked Equations （SIMPLE） algorithm is proposed. This method could be used in both coupling computation of para- chute FSI and flow field analysis. Both fiat circular parachute and conical parachute are modeled and simulated by this new method. Flow field characteristics at various angles of attack are further simulated for the conical parachute model. Compari- son with the space-time FSI technique shows that this method also provides similar and reasonable results.展开更多
An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to bla...An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and ParaInetric Polynomial Method. After getting the solution of the unsteady flow field, the work done by the unsteay aerody natnic force acting on the blade can be obtained. The negative or positive work is the criterion of the aeroelastic stability Numerical results indicate that there are instabilities of the torsional vibration in some boency bands.展开更多
In order to shorten aero-engine axial length,substituting the traditional long chord thick strut design accompanied with the traditional low pressure(LP) stage nozzle,LP turbine is integrated with intermediate turbine...In order to shorten aero-engine axial length,substituting the traditional long chord thick strut design accompanied with the traditional low pressure(LP) stage nozzle,LP turbine is integrated with intermediate turbine duct(ITD).In the current paper,five vanes of the first stage LP turbine nozzle is replaced with loaded struts for supporting the engine shaft,and providing oil pipes circumferentially which fulfilled the areo-engine structure requirement.However,their bulky geometric size represents a more effective obstacle to flow from high pressure(HP) turbine rotor.These five struts give obvious influence for not only the LP turbine nozzle but also the flowfield within the ITD,and hence cause higher loss.Numerical investigation has been undertaken to observe the influence of the Nozzle-Strut integrated design concept on the flowfield within the ITD and the nearby nozzle blades.According to the computational results,three main conclusions are finally obtained.Firstly,a noticeable low speed area is formed near the strut's leading edge,which is no doubt caused by the potential flow effects.Secondly,more severe radial migration of boundary layer flow adjacent to the strut's pressure side have been found near the nozzle's trailing edge.Such boundary layer migration is obvious,especially close to the shroud domain.Meanwhile,radial pressure gradient aggravates this phenomenon.Thirdly,velocity distribution along the strut's pressure side on nozzle's suction surface differs,which means loading variation of the nozzle.And it will no doubt cause nonuniform flowfield faced by the downstream rotor blade.展开更多
The controlled equations defined in a physical plane are changed into those in a computational plane with coordinate transformations suitable for different Mach number M The computational area is limited in the body s...The controlled equations defined in a physical plane are changed into those in a computational plane with coordinate transformations suitable for different Mach number M The computational area is limited in the body surface and in the vicinities of detached shock wave and sonic line.Thus the area can be greatly cut down when the shock wave moves away from the body surface as M∝→1.Highly accurate,total variation diminishing(TVD)finite-difference schemes are used to calculate the low supersonic flowfield around a sphere.The stand-off distance,location of sonic line,etc.are well comparable with experimental data.The long pending problem concerning a flow passing a sphere at 1.3≥M∝>1 has been settled,and some new results on M∝=1.05 have been presented展开更多
This paper describes the design of four types of swirlers which produce different velocity profiles.The data of confined turbulent swirling flowfields are obtained from experiments and numerical calculations.The actua...This paper describes the design of four types of swirlers which produce different velocity profiles.The data of confined turbulent swirling flowfields are obtained from experiments and numerical calculations.The actual flow profiles at the swirler exit basically agree with the desired profiles. Two kinds of turbulence models,k-ε model and DDC model,are used to predict the flowfields produced by swirl augmentors.The results show that the DDC model,based on interaction between dissipation and dispersion,can overcome the defect of k-ε model and predict the swirling flowfields more accurately than k-ε model.展开更多
基金supported by the National Key Research and Development Program of China(No.2019YFA0405300)the National Natural Science Foundation of China(No.12272405).
文摘Flowfield inverse design can obtain the desired flow and contour with high design efficiency,short design cycle,and small modification need.In this study,the Euler equations are formulated in the stream-function coordinates and combined with the given boundary conditions to derive a gridless space-marching method for the inverse design of subsonic,transonic,and supersonic flowfields.Designers can prescribe the flow parameters along the reference streamline to design flowfields and aerodynamic contours.The method is validated by the theoretical transonic solution,computational fluid dynamics,and experimental data,respectively.The method supports the fabrication of a Mach 2.0 single expansion tunnel.The calibration data agree well with the prescribed pressure distribution.The method is successfully applied to inverse design of contractions,nozzles,and asymmetric channels.Compared to classical analytic contractions,the contractions designed by the space-marching method provide a more accurate transonic flow.Compared to the classical Sivells’nozzle,the nozzle designed by the space-marching method provides a smaller workload,a more flexible velocity distribution,a 20%reduction in length,and an equally uniform flow.Additionally,the space-marching method is applied to design the asymmetric channels under various Mach numbers.These asymmetric channels perfectly eliminate Mach waves,achieving the shock-free flow turning and high flow uniformity.These results validate the feasibility of the space-marching method,making it a good candidate for the inverse design of subsonic,transonic,and supersonic internal flowfields and aerodynamic contours.
基金supported by the Research Funding of Hangzhou International Innovation Institute of Beihang University,China(No.2024KQ143).
文摘Distributed ducted propellers hold significant promise for propulsion systems in Advanced Air Mobility(AAM) due to their high efficiency, low noise, and enhanced redundancy and safety. However, a standardized benchmark for comparing the aerodynamic characteristics of different ducted propeller configurations remains lacking. Including additional ducted propellers can further complicate the flow field. This paper proposes an equivalent design method for ducted propellers based on the momentum theorem and similarity criteria, introducing three equivalent ducted propeller cases. Transient numerical simulations are conducted using the sliding mesh model. The three cases produce comparable thrust while consuming the same power, with the volume of distributed ducted propellers being reduced by over 29% compared to the single ducted propeller. This study investigates the effect of rotational frequency on aerodynamic performance under hovering conditions. While propeller performance demonstrates low sensitivity to variations in rotational frequency, duct performance exhibits high sensitivity. The research further examines how rotational frequency changes the pressure difference between the duct leading edge and trailing edge. Based on a sensitivity analysis of aerodynamic performance, the flow field mechanisms under different rotational consistency are examined for the case with one duct and two propellers. Differences in aerodynamic performance are attributed to the airflow velocity gradient differences at the duct leading edge and the flow separation characteristics on the crossing side. These findings are significant for enhancing the performance of distributed ducted propellers and improving aircraft controllability.
基金Advanced Jet Propulsion Innovation Center,AEAC(Project ID.HKCX2021-01-021)The Fundamental Research Funds for the Central Universities(Project ID.501XTCX2023146001)Science Center for Gas Turbine Project(P2022-A-II-006-001)。
文摘This paper focuses on the optimization of the outlet temperature field of a hydrogen micromixing diffusion combustor for a micro-turbojet engine with a thrust of 20kgf.The joint simulation optimization platform was established combiningWorkbench and UG and the multi-parameter driven optimization design process was developed.The surrogate models and genetic algorithms were employed to investigate the influences of key parameters on the hotspot temperature at the combustor exit.It was found that smaller diameters of the dilution holes and positions further from the exit lead to lower hotspot temperatures.Additionally,an optimal solution for achieving a uniform temperature distribution at the combustor outlet was obtained.This solution involves a single row of dilution holes on both the inner and outer walls of the flame tube,arranged in an alternating axial and angular pattern.Through aerothermal process analysis,it was determined that the outlet temperature distribution coefficient(OTDF)of the combustion chamber is below 0.2.Meanwhile,the axial dimension of the flame is short,approximately one-third of the flame tube length.The conclusions derived from this study provide important guidance for the design of hydrogen micromix diffusion combustor.
基金supported by the National Natural Science Foundation of China(No.11272150)
文摘In order to calculate the unsteady aerodynamic characteristics of a tilt-rotor in a conver- sion mode, a virtual blade model （VBM） and an real blade model （RBM） are established respec- tively. A new multi-layer moving-embedded grid technique is proposed to reduce the numerical dissipation of the tilt-rotor wake in a conversion mode. In this method, a grid system generated abound the rotor accounts for rigid blade motions, and a new searching scheme named adaptive inverse map （AIM） is established to search corresponding donor elements in the present moving- embedded grid system to translate information among the different computational zones. A dual-time method is employed to fulfill unsteady calculations on the flowfield of the tilt-rotor, and a second-order centered difference scheme considering artificial viscosity is used to calculate the flux. In order to improve the computing efficiency, the single program multiple data （SPMD） model parallel acceleration technology is adopted, according to the characteristic of the current grid system. The lift and drag coefficients of an NACA0012 airfoil, the dynamic pressure distributions below a typical rotor plane, and the sectional pressure distributions on a three-bladed Branum- Tung tilt-rotor in hover flight are calculated respectively, and the present VBM and RBM are val- idated by comparing the calculated results with available experimental data. Then, unsteady aero- dynamic forces and flowfields of an XV-15 tilt-rotor in different modes, such as a fixed conversion mode at different tilt angles （15°, 30°, 60°） and a whole conversion mode which converses from 0° to 90°, are numerically simulated by the VBM and RBM respectively. By analyses and comparisons on the simulated results of unsteady aerodynamic forces of the tilt-rotor in different modes, some meaningful conclusions about distorted blade-tip vortex distribution and unsteady aerodynamic force variation in a conversion mode are obtained, and these investigation results could provide a good foundation for tilt-rotor aircraft design in the future.
文摘This paper studies numerically the influence of the tip clearance on the three dimensional viscous flowfield and performance of the NASA Low Speed Centrifugal Compressor (LSCC) impeller with a vaneless diffuser A three dimensional viscous code developed by the authors is applied with several acceleration methods: local time step, multigrid and residual smoothing The computations were performed under several operating conditions with four different tip clearance sizes(0 0%,50%,100% and 200% design t...
基金Supported by the National Natural Science Foundation of China(No.59976023)
文摘In the commercial utilization of rigid ceramic filters, the performance of pulse cleaning has crucial effects on the long-term stable operation. In order to get a clear insight into the nature of this cleaning process and provide a solid basis for industrial applications, the flow in ceramic candle filter was investigated. The flow in the pulse-jetspace and inside the ceramic candle is regarded as two- dimensional, unsteady, compressible flow, and numerical simulation is carried out by computational fluid dynamics. The numerical predictions of flow field are in good agreement with the experimental measurements. Effects of the candle diameter, the separation distance between the nozzle and the candle injector and the length of the candle on the flowfield have been numerically analyzed to provide the basis for the optimum design of the pulse cleaning system.
基金supported by the Fundamental Research Funds for the Central Universities of China(Grant 310201906zy009)the Basic Research Plan of Natural Science in Shanxi Provincei-General Project(Youth)(Grant 2019JQ-132).
文摘In this work,the flow fields in three-dimensional(3D)sidewall compression inlets are investigated theoretically and numerically.Combining spatial dimension reduction theory with the shock dynamics theory,a detailed analysis of the flowfield in the compression part of an inlet is proposed.Using this analytical approach,wave configurations are determined and flowfield parameters are solved;numerical simulations are conducted to validate these theoretical results.The effects of the attack angle and yaw angle on the pressure ratio,wave structures,and total pressure recovery performance are discussed in detail.Findings offer an effective way to study shock/shock interaction(SSI)in sidewall inlets,which is essential to the designing of such inlets.
基金the National Natural Science Foundation of China (1047202510672036)the Natural Science Foundation of Liaoning Province,China (20032109)
文摘To study the airflow distribution in human nasal cavity during respiration and the characteristic parameters of nasal structure, three-dimensional, anatomically accurate representations of 30 adult nasal cavity models were recons- tructed based on processed tomography images collected from normal people. The airflow fields in nasal cavities were simulated by fluid dynamics with finite element software ANSYS. The results showed that the difference of human nasal cavity structure led to different airflow distribution in the nasal cavities and variation of the main airstream passing through the common nasal meatus. The nasal resistance in the regions of nasal valve and nasal vestibule accounted for more than half of the overall resistance. The characteristic model of nasal cavity was extracted on the basis of characteristic points and dimensions deduced from the original models. It showed that either the geometric structure or the airflow field of the two kinds of models was similar. The characteristic dimensions were the characteristic parameters of nasal cavity that could properly represent the original model in model studies on nasal cavity.
基金Project(2006AA09Z235)supported by the National High Technology Research and Development Program of ChinaProject(CX2009B003)supported by Hunan Provincial Innovation Foundation For Postgraduate,China
文摘Autonomous underwater vehicles （AUVs） navigating on the sea surface are usually required to complete the communication tasks in complex sea conditions. The movement forms and flow field characteristics of a multi-moving state AUV navigating in head sea at high speed were studied. The mathematical model on longitudinal motion of the high-speed AUV in head sea was established with considering the hydrodynamic lift based on strip theory, which was solved to get the heave and pitch of the AUV by Gaussian elimination method. Based on this, computational fluid dynamics （CFD） method was used to establish the mathematical model of the unsteady viscous flow around the AUV with considering free surface effort by using the Reynolds-averaged Navier-Stokes （RANS） equations, shear-stress transport （SST） k-w model and volume of fluid （VOF） model. The three-dimensional numerical wave in the computational field was realized through defining the unsteady inlet boundary condition. The motion forms of the AUV navigating in head sea at high speed were carried out by the program source code of user-defined function （UDF） based on dynamic mesh. The hydrodynamic parameters of the AUV such as drag, lift, pitch torque, velocity, pressure and wave profile were got, which reflect well the real ambient flow field of the AUV navigating in head sea at high speed. The computational wave profile agrees well with the experimental phenomenon of a wave-piercing surface vehicle. The force law of the AUV under the impacts of waves was analyzed qualitatively and quantitatively, which provides an effective theoretical guidance and technical support for the dynamics research and shape design of the AUV in real complex environnaent.
文摘Experiment measurement is adapted to study the secondary flow of turbine.The subsonic stator experiment flow tunnel is set up.Two different inlet velocities and three different stator heights are applied.The method of a rotating slanted hotwire is introduced to measure the stator outlet three-dimensional flow field.The procedure for solving the mean three-dimensional velocity component involving the least-squares technique can be accomplished via the LSQNONLIN optimization function of Matlab.Under different work conditions,the stator outlet secondary flow is more intense at higher inlet flux.Moreover,the shortest stator height will lead to the most intense secondary flow,which gains the largest axial velocity component(w) and radial velocity component (u),but the smallest circumferential velocity component(v).
文摘Numerical simulations are presented about the effects of gas rarefaction on hypersonic flow field.Due to the extremely difficult experiment,limited wind-tunnel conditions and high cost,most problems in rarefied flow regime are investigated through numerical methods,in which the direct simulation Monte-Carlo(DSMC)method is widely adopted.And the unstructured DSMC method is employed here.Flows around a vertical plate at a given velocity 7 500 m/s are simulated.For gas rarefaction is judged by the free-stream Knudsen number(Kn),two vital factors are considered:molecular number density and the plate′s length.Cases in which Kn varies from 0.035 to13.36 are simulated.Flow characters in the whole rarefied regime are described,and flow-field structure affected by Knis analyzed.Then,the dimensionless position D*of a certain velocity in the stagnation line is chosen as the marker of flow field to measure its variation.Through flow-field tracing and least-square numerical method analyzing,it is proved that hypersonic rarefied flow field expands outward linearly with the increase of 1/2Kn.An empirical method is proposed,which can be used for the prediction of the hypersonic flow-field structure at a given inflow velocity,especially the shock wave position.
文摘The structure of inert turbulent flows, stabilized in a Bluff-Body burner, is studied considering different volumetric flows for Nitrogen jet and annular air in coflow configuration. Flowfield analysis on Bluff-Body burner is essential to improve the knowledge about this burner, which plays an important role in industrial applications. Thus, vector velocity field is performed, employing Particle Image Velocimetry technique. Also, an uncertainty analysis is performed considering parameters involved in this technique yielding 6% to velocity measurements. The acquired information produces the results based in flowfield structure, which are presented in terms of statistical momentum and Reynolds stress, in which Boussinesq Hypothesis is considered to incompressible flows. However, this hypothesis fails in certain conditions. In this way, is possible to comprehend and provide experimental data from the turbulent effects on the flowfield and also contribute to predict the combustion flows, in order to enable the validation and develop numerical models.
文摘High-pressure shallow(gas/water)flow is often hidden in the deepwater seabed,so penetrating shallowflow in drilling without BOP will be highly risky.In this case,the conventional well killing method to balance the formation pressure with back pressure generated by well head equipment is no longer suitable.Based on the analysis of structural characteristics of domestic and foreign multi-phase mixing systems,a ZM-2 drillingfluid density adjustment mixing device with independent intellectual property right was developed according to the principles of dy-namic well killing.The device is mainly composed of a throttle valve,a high-precision electromagneticflowmeter,a mixer,dumbbell-shaped nozzles,connecting pipes and other components.Fixed on the mixer are three inlets tofill heavy mud,seawater and additives.Opposed jetting is adopted to realize rapid and uniform mixing offluids with different densities.A laboratory test was conducted to work out the relationship between throttle opening and injectionflow rate and establish a linear relationship between killingfluid density and heavy mudflow.The results offield test conducted in the Nanhai No.8 drill ship showed that the mixing device was stable in operation and excellent in mixing performance.The density difference of ingredient mixture could be controlled within 0.05 g/cm3 after the mixtureflowed out of the mixing chamber of the mixer of about 0.3 m long,so such high precision can meet the requirement of dynamic well killing.
基金supported by the National Natural Science Foundation of China (Grant No.11972139 and 52125603)the Fundamental Research Funds for the Central Universities (HIT.BRET.2021006 and FRFCU5710094620).
文摘Accurate acquisition of the distribution offlow parameters inside the supersonic combustor is of great significance for hypersonicflight control.It is an interesting attempt to introduce a data-driven model to a supersonic combustor forflowfield prediction.This paper proposes a novel method for predicting theflowfield in a dual-mode combustor.Aflowfield prediction convolutional neural network with multiple branches is built.Numerical investiga-tions for a strut variable geometry combustor have been conducted to obtainflowfield data for training the network as aflowfield prediction model.Richflowfield data are obtained by changing the equivalent ratio,incomingflow condition and geometry of the supersonic combustor.The Mach number distribution can be obtained from the trainedflowfield prediction model using the combustor wall pressure as input with high accuracy.The accuracy offlowfield prediction is discussed in several aspects.Further,the combustion mode detection is im-plemented on the predictionflowfield.
基金supported by the Doctorate Creation Foundation of Northwestern Polytechnical University (Grant No. CX200902)
文摘A rapid approach to hypersonic aeroheating predictions in the stagnation region and downstream is developed in the present paper.The engineering method is used to calculate inviscid hypersonic flowfields to reduce time cost,and a combination of the mass flow balance technique and the axisymmetric analog is proposed to account for the entropy swallowing effects.A three-dimensional linear method is derived to fit the vehicle surface flowfields.Then a new axisymmetric analog method based on linear flowfields and linear surface equations is developed,with the complexity and computational cost reduced dramatically.In the stagnation region,an implicit surface fitting is introduced to approximate the primary curvatures and a robust aeroheating prediction method is constructed.The proposed approach is verified on a variety of configurations including spherically blunted cone,double ellipsoid and aerospace vehicle.Numerical results indicate the followings:1)The approach predicts aeroheating in about one second and the results agree well with CFD simulations and wind-tunnel measurements;2)with the help of entropy correction,the precision is further improved in the streamline diverging regions on the vehicle surface,while little improvement is found after entropy correction in the regions where the streamlines do not diverge.
基金supported by the National Natural Science Foundation of China (Grant No. 10577003)Monash University of Australia
文摘A numerical simulation method for parachute Fluid-Structure Interaction （FSI） problem using Semi-Implicit Method for Pres- sure-Linked Equations （SIMPLE） algorithm is proposed. This method could be used in both coupling computation of para- chute FSI and flow field analysis. Both fiat circular parachute and conical parachute are modeled and simulated by this new method. Flow field characteristics at various angles of attack are further simulated for the conical parachute model. Compari- son with the space-time FSI technique shows that this method also provides similar and reasonable results.
文摘An algorithm for computing the 3-D oscillating flow field of the blade passage under the torsional vibra-tion of the rotor is applied to analyze the stability in turbomachines. The induced fiow field responding to blade vibration is computed by Oscillating Fluid Mechanics Method and ParaInetric Polynomial Method. After getting the solution of the unsteady flow field, the work done by the unsteay aerody natnic force acting on the blade can be obtained. The negative or positive work is the criterion of the aeroelastic stability Numerical results indicate that there are instabilities of the torsional vibration in some boency bands.
基金supported by grants from the National Natural Science Foundation of China(No.51306177)
文摘In order to shorten aero-engine axial length,substituting the traditional long chord thick strut design accompanied with the traditional low pressure(LP) stage nozzle,LP turbine is integrated with intermediate turbine duct(ITD).In the current paper,five vanes of the first stage LP turbine nozzle is replaced with loaded struts for supporting the engine shaft,and providing oil pipes circumferentially which fulfilled the areo-engine structure requirement.However,their bulky geometric size represents a more effective obstacle to flow from high pressure(HP) turbine rotor.These five struts give obvious influence for not only the LP turbine nozzle but also the flowfield within the ITD,and hence cause higher loss.Numerical investigation has been undertaken to observe the influence of the Nozzle-Strut integrated design concept on the flowfield within the ITD and the nearby nozzle blades.According to the computational results,three main conclusions are finally obtained.Firstly,a noticeable low speed area is formed near the strut's leading edge,which is no doubt caused by the potential flow effects.Secondly,more severe radial migration of boundary layer flow adjacent to the strut's pressure side have been found near the nozzle's trailing edge.Such boundary layer migration is obvious,especially close to the shroud domain.Meanwhile,radial pressure gradient aggravates this phenomenon.Thirdly,velocity distribution along the strut's pressure side on nozzle's suction surface differs,which means loading variation of the nozzle.And it will no doubt cause nonuniform flowfield faced by the downstream rotor blade.
基金Project supported by the National Natural Science Foundation of China
文摘The controlled equations defined in a physical plane are changed into those in a computational plane with coordinate transformations suitable for different Mach number M The computational area is limited in the body surface and in the vicinities of detached shock wave and sonic line.Thus the area can be greatly cut down when the shock wave moves away from the body surface as M∝→1.Highly accurate,total variation diminishing(TVD)finite-difference schemes are used to calculate the low supersonic flowfield around a sphere.The stand-off distance,location of sonic line,etc.are well comparable with experimental data.The long pending problem concerning a flow passing a sphere at 1.3≥M∝>1 has been settled,and some new results on M∝=1.05 have been presented
文摘This paper describes the design of four types of swirlers which produce different velocity profiles.The data of confined turbulent swirling flowfields are obtained from experiments and numerical calculations.The actual flow profiles at the swirler exit basically agree with the desired profiles. Two kinds of turbulence models,k-ε model and DDC model,are used to predict the flowfields produced by swirl augmentors.The results show that the DDC model,based on interaction between dissipation and dispersion,can overcome the defect of k-ε model and predict the swirling flowfields more accurately than k-ε model.
