For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline wi...For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline without stagnation point,vorticity either is equal to zero everywhere,or it is non zero at all.The pattern of vortex lines behind the three-dimensional detached bow shock wave is specified.展开更多
With the increasing of computing ability,large-scale simulations have been generating massive amounts of data in aerodynamics.Sort-last parallel rendering is the most classical image compositing method for large-scale...With the increasing of computing ability,large-scale simulations have been generating massive amounts of data in aerodynamics.Sort-last parallel rendering is the most classical image compositing method for large-scale scientific visualization.However,in the stage of image compositing,the sort-last method may suffer from scalability problem on large-scale processors.Existing image compositing algorithms tend to perform well in certain situations.For instance,Direct Send is well on small and medium scale;Radix-k gets well performance only when the k-value is appropriate and so on.In this paper,we propose a novel method named mSwap for scientific visualization in aerodynamics,which uses the best scale of processors to make sure its performance at the best.mSwap groups the processors that we can use with a(m,k)table,which records the best combination of m(the number of processors in subgroup of each group)and k(the number of processors in each group).Then in each group,using a m-ary tree to composite the image for reducing the communication of processors.Finally,the image is composited between different groups to generate the final image.The performance and scalability of our mSwap method is demonstrated through experiments with thousands of processors.展开更多
A dynamic nonlinear algebraic model with scale-similarity dynamic procedure(DNAM-SSD)is proposed for subgrid-scale(SGS)stress in large-eddy simulation of turbulence.The model coefficients of the DNAM-SSD model are ada...A dynamic nonlinear algebraic model with scale-similarity dynamic procedure(DNAM-SSD)is proposed for subgrid-scale(SGS)stress in large-eddy simulation of turbulence.The model coefficients of the DNAM-SSD model are adaptively calculated through the scale-similarity relation,which greatly simplifies the conventional Germano-identity based dynamic procedure(GID).The a priori study shows that the DNAM-SSD model predicts the SGS stress considerably better than the conventional velocity gradient model(VGM),dynamic Smagorinsky model(DSM),dynamic mixed model(DMM)and DNAM-GID model at a variety of filter widths ranging from inertial to viscous ranges.The correlation coefficients of the SGS stress predicted by the DNAM-SSD model can be larger than 95%with the relative errors lower than 30%.In the a posteriori testings of LES,the DNAM-SSD model outperforms the implicit LES(ILES),DSM,DMM and DNAM-GID models without increasing computational costs,which only takes up half the time of the DNAM-GID model.The DNAM-SSD model accurately predicts plenty of turbulent statistics and instantaneous spatial structures in reasonable agreement with the filtered DNS data.These results indicate that the current DNAM-SSD model is attractive for the development of highly accurate SGS models for LES of turbulence.展开更多
At present,the control capability of dielectric barrier discharge(DBD)plasma actuation covers the flow velocity range of helicopter’s retreating blades,so it is necessary to extend it to the dynamic stall control of ...At present,the control capability of dielectric barrier discharge(DBD)plasma actuation covers the flow velocity range of helicopter’s retreating blades,so it is necessary to extend it to the dynamic stall control of rotor airfoils.A DBD plasma actuator was adopted to control the dynamic stall of an oscillating CRA309 airfoil in this paper.The effectiveness of alternating current(AC)DBD plasma actuation on reducing the area of lift hysteresis loop of the oscillating airfoil was verified through pressure measurements at a Reynolds number of 5.2×10^(5).The influence of actuation parameters on the airfoil’s lift and moment coefficients was studied.Both steady and unsteady actuation could effectively reduce the hysteresis loop area of the lift coefficients.The flow control effect of dynamic stall was strongly dependent on the history of angle of attack.Compared with the steady actuation,unsteady actuation had more obvious advantages in dynamic stall control,with reducing the area of lift hysteresis loop by more than 30%.The effects of plasma actuation on the airfoil’s flow field at both upward and downward stages were discussed at last.展开更多
A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments.An analysis for three Reynolds numbers is conducted at various angles of attack.Th...A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments.An analysis for three Reynolds numbers is conducted at various angles of attack.The computations are performed by means of the TAU-Code and the FEM Carat++solver.Wind-tunnel tests are carried out for performance analysis and to estimate the accuracy of the computations.In the results,the advantages of an elasto-flexible-lifting-surface concept are highlighted by comparing the formvariable surface to its rigid counterpart.The flexibility of the material and its adaptivity to the freestream allow the membrane to adjust its shape to the pressure distribution.For positive angles of attack,the airfoil’s camber increases resulting in an increase in the wing lifting capacity.Furthermore,the stall onset is postponed to higher angles of attack and the abrupt decrease in the lift is replaced by a gradual loss of it.展开更多
This paper presents an extensive review of existing techniques used in estimating design wind pressures considering Reynolds number and turbulence effects,as well as a case study of a reference building investigated e...This paper presents an extensive review of existing techniques used in estimating design wind pressures considering Reynolds number and turbulence effects,as well as a case study of a reference building investigated experimentally.We shed light on the limitations of current aerodynamic testing techniques,provisions in design standards,and computational fluid dynamics(CFD)methods to predict wind-induced pressures.The paper highlights the reasons for obstructing the standardization of the wind tunnel method.Moreover,we introduce improved experimental and CFD techniques to tackle the identified challenges.CFD provides superior and efficient performance by employing wall-modeled large-eddy simulation(WMLES)and hybrid RANS-LES models.In addition,we tested a large-scale building model and compared the results with published small-scale data.The findings reinforce our hypothesis concerning the scaling issues and Reynolds number effects in aerodynamic testing.展开更多
To increase the efficiency and robustness of stability-based transition prediction in flow simulations, simplified methods are introduced to substitute direct stability analyses for rapid disturbance growth prediction...To increase the efficiency and robustness of stability-based transition prediction in flow simulations, simplified methods are introduced to substitute direct stability analyses for rapid disturbance growth prediction. For low-speed boundary layers, these methods are mainly established based on self-similar assumptions, which are not applicable to non-similar boundary layers in hypersonic flows. The objective of this article is to investigate the application of surrogate models to stability analysis of non-similar flows over blunt cones, focused on parameterization of boundary-layer (BL) profiles. Firstly, correlations between BL edge and profile parameters are analyzed, along with self-similar flow parameters and discrete points on BL profiles, which present four groups of BL characteristic parameters. Secondly, using these parameters as inputs, surrogate models are built for disturbance growth prediction over an MF-1 blunt cone. Results show that, surrogate models using four BL edge parameters and a BL shape factor {Ue, Te, ρe, ηe, H12} for stability analysis can achieve comparable accuracy with those using 16 discrete BL profile parameters, which are more precise than those using merely self-similar parameters or BL edge parameters. Thirdly, the established surrogate models are validated by stability analysis and transition prediction over the MF-1 blunt cone in flight experiments at the instants of t = 17 s ~ 22 s. Compared with direct linear stability analyses, the mean relative error of predicted disturbance growth rates by surrogate models is 8.0% and the maximum relative error of N factor envelopes is 6.6%, which indicates feasible applications of surrogate models to stability analysis and transition prediction of non-similar boundary layers in hypersonic flows.展开更多
Despite over fifty years of research on shock wave boundary layer effects and interactions,many related technical issues continue to be controversial and debated.The present survey provides an overview of the present ...Despite over fifty years of research on shock wave boundary layer effects and interactions,many related technical issues continue to be controversial and debated.The present survey provides an overview of the present state of knowledge on such effects and interactions,including discussions of:(i)general features of shock wave interactions,(ii)test section configurations for investigation of shock wave boundary layer interactions,(iii)origins and sources of unsteadiness associated with the interaction region,(iv)interactions which included thermal transport and convective heat transfer,and(v)shock wave interaction control investigations.Of particular interest are origins and sources of low-frequency,large-scale shock wave unsteadiness,flow physics of shock wave boundary layer interactions,and overall structure of different types of interactions.Information is also provided in regard to shock wave investigations,where heat transfer and thermal transport were important.Also considered are investigations of shock wave interaction control strategies,which overall,indicate that no single shock wave control strategy is available,which may be successfully applied to different shock wave arrangements,over a wide range of Mach numbers.Overall,the survey highlights the need for additional understanding of fundamental transport mechanisms,as related to shock waves,which are applicable to turbomachinery,aerospace,and aeronautical academic disciplines.展开更多
The combination of Cartesian grid and the adaptive mesh refinement(AMR)technology is an effective way to handle complex geometry and solve complex flow problems.Some high-efficiency Cartesian-based AMR libraries have ...The combination of Cartesian grid and the adaptive mesh refinement(AMR)technology is an effective way to handle complex geometry and solve complex flow problems.Some high-efficiency Cartesian-based AMR libraries have been developed to handle dynamic changes of the grid in parallel but still can not meet the unique requirements of simulating flow around objects.In this paper,we propose an efficient Cartesian grid generation method and an information transmission approach for the wall boundary to parallelize the implementation of ghost-cell method(GCM).Also,the multi-valued ghost-cell method to handle multi-value points is improved to adapt to the parallel framework.Combining the mentioned methodologies with the open-source library p4est,an automatic and efficient simulation of compressible flow is achieved.The overall performance of the methodology is tested through a wide range of inviscid/viscous flow cases.The results indicate that the capability and parallel scalability of the present numerical methodology for solving multiple types of flows,involving shock and vortices,multi-body flow and unsteady flows are agreeable as compared with related reference data.展开更多
Cryogenic wind tunnel is a sophisticated aerodynamics ground test faility,which operates in cryogenic temperature with injection of liquid nitrogen.The multi-variable,nonlinear and coupled dynamics existing between th...Cryogenic wind tunnel is a sophisticated aerodynamics ground test faility,which operates in cryogenic temperature with injection of liquid nitrogen.The multi-variable,nonlinear and coupled dynamics existing between the temperature,pressure and Mach number in the tunnel,poses great challenges for the effective control of the tunnel.L_(1) adaptive control is a new control methodology developed in recent years with good robustness properties,which has good potentials to address these challenges.But this control method does not provide full adaptive feedforward control in its generic structure.In the paper,adaptive feedforward control action is introduced into the standard L_(1) adaptive control architecture for nonlinear systems in the presence of matched un-modeled dynamics.This new control structure is applied to the stagnation pressure control in a cryogenic wind tunnel,which could also be used for the control of temperature and Mach number in the tunnel.This new method could effectively compensate known disturbances with linear gain uncertainty,which occur in the nonlinear systems,while retaining the closed-loop control performance of L_(1) adaptive control.After the proof and discussions on the stability of this method,simulations of the stagnation pressure control in the wind tunnel are presented.The results and analysis demonstrate the effectiveness of the proposed control architecture.展开更多
Prediction of the coupled conduction-radiation heat transfer in composite materials with periodic structure is important in high-temperature applications of the materials. The temperature dependence of thermal propert...Prediction of the coupled conduction-radiation heat transfer in composite materials with periodic structure is important in high-temperature applications of the materials. The temperature dependence of thermal properties complicates the problem. In this work, a multiscale model is proposed for the conduction-radiation heat transfer in periodic composite materials with temperature-dependent thermal properties. Homogenization analysis of the coupled conduction and radiative transfer equations is conducted, in which the temperature dependence of thermal properties is considered. Both the macroscopic homogenized equations and the local unit cell problems are derived. It is proved that the macroscopic average temperature can be used in the unit cell problems for the first-order corrections of the temperature and radiative intensity, and the calculations of effective thermal properties. The temperature dependence of thermal properties only influences the higher-order corrections. A multiscale numerical method is proposed based on the analysis. The Gaussian process (GP) regression is coupled into the multiscale algorithm to build a correlation between thermal properties and temperature for the macroscale iterations and prevent the repetitive solving of unit cell problems. The GP model is updated by additional solutions of unit cell problems during the iteration according to a variance threshold. Numerical simulations of conduction-radiation heat transfer in composite with isotropic and anisotropic periodic structures are used to validate the proposed multiscale model. It is found that the accuracy and efficiency of the multiscale method can be guaranteed by using a proper variance threshold for the GP model. The multiscale model can provide both the average temperature and radiative intensity fields and their detailed fluctuations due to the local structures.展开更多
This paper presents a robust sharp-interface immersed boundary method for simulating inviscid compressible flows over stationary and moving bodies.The flow field is governed by Euler equations,which are solved by usin...This paper presents a robust sharp-interface immersed boundary method for simulating inviscid compressible flows over stationary and moving bodies.The flow field is governed by Euler equations,which are solved by using the open source library OpenFOAM.Discontinuities such as those introduced by shock waves are captured by using Kurganov and Tadmor divergence scheme.Wall-slip boundary conditions are enforced at the boundary of body through reconstructing flow variables at some ghost points.Their values are obtained indirectly by interpolating from their mirror points.A bilinear interpolation is employed to determine the variables at the mirror points from boundary conditions and flow conditions around the boundary.To validate the efficiency and accuracy of this method for simulation of high-speed inviscid compressible flows,four cases have been simulated as follows:supersonic flow over a 15°angle wedge,transonic flow past a stationary airfoil,a piston moving with supersonic velocity in a shock tube and a rigid circular cylinder lift-off from a flat surface triggered by a shock wave.Compared to the exact analytical solutions or the results in literature,good agreement can be achieved.展开更多
Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discret...Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discrete unified gas kinetic scheme(DUGKS)is a recently developed numerical approach for simulating multiscale flows based on kinetic models.The finite-volume DUGKS differs from the classical kinetic methods in the modeling of gas evolution and the reconstruction of interface flux.Particularly,the distribution function at a cell interface is reconstructed from the characteristic solution of the kinetic equation in space and time,such that the particle transport and collision effects are coupled,accumulated,and evaluated in a numerical time step scale.Consequently,the cell size and time step of DUGKS are not passively limited by the particle mean-free-path and relaxation time.As a result,the DUGKS can capture the flow behaviors in all regimes without resolving the kinetic scale.Particularly,with the variation of the ratio between numerical mesh size scale and kinetic mean free path scale,the DUGKS can serve as a self-adaptive multiscale method.The DUGKS has been successfully applied to a number of flow problems with multiple flow regimes.This paper presents a brief review of the progress of this method.展开更多
The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities.In this work,the oblique-mode breakdown,as one o...The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities.In this work,the oblique-mode breakdown,as one of the most available transition mechanisms,is studied using the nonlinear parabolized stability equations(NPSE)with consideration of the thermal-chemical non-equilibrium effects.The flow over a blunt cone is computed at a free-stream Mach-number of 15.The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture.It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient.In comparison to the CPG flow,the TCNE effects destabilize the second mode and push upstream the N factor envelope.The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.展开更多
The hypersonic boundary layer(HBL)transition on a slender cone at moderate incidence is studied via a symmetry-based length model:the SED-SL model.The SED-SL specifies an analytic stress length function(which defines ...The hypersonic boundary layer(HBL)transition on a slender cone at moderate incidence is studied via a symmetry-based length model:the SED-SL model.The SED-SL specifies an analytic stress length function(which defines the eddy viscosity)describing a physically sound two-dimensional multi-regime structure of transitional boundary layer.Previous studies showed accurate predictions,especially on the drag coefficient,by the SED-SL for airfoil flows at different subsonic Mach numbers,Reynolds numbers and angles of attack.Here,the SED-SL is extended to compute the hypersonic heat transfer on a 7∘half-angle straight cone at Mach numbers 6 and 7 and angles of attack from 0∘to 6∘.It is shown that a proper setting of the multi-regime structure with three parameters(i.e.a transition center,an after-transition near-wall eddy length,and a transition width quantifying transition overshoot)yields an accurate description of the surface heat fluxes measured in wind tunnels.Uniformly good agreements between simulations and measurements are obtained from windward to leeward side of the cone,implying the validity of the multi-regime description of the transition independent of instability mechanisms.It is concluded that a unified description for the HBL transition of cone is found,and might offer a basis for developing a new transition model that is simultaneously of computational simplicity,sound physics and greater accuracy.展开更多
In this era of fast-depleting natural resources,the hike in fuel prices is ever-growing.With stringent norms over environmental policies,the automotive manufacturers are on a voyage to produce efficient vehicles with ...In this era of fast-depleting natural resources,the hike in fuel prices is ever-growing.With stringent norms over environmental policies,the automotive manufacturers are on a voyage to produce efficient vehicles with lower emissions.High-speed cars are at a stake to provide uncompromised performance but having strict rules over emissions drives the companies to approach through a different route to keep the demands of performance intact.One of the most sought-after ways is to improve the aerodynamics of the vehicles.Drag force is one of the major setbacks when it comes to achieving high speeds when the vehicle is in motion.This research aims to examine the effects of different add on devices on the vehicle to reduce drag and make the vehicle aerodynamically streamlined.A more streamlined vehicle will be able to achieve high speeds and consequently,the fuel economy is also improved.The three-dimensional car model is developed in SOLIDWORKS v17.Computational Fluid Dynamics(CFD)is performed to understand the effects of these add on devices.CFD is carried out in the ANSYS^(TM) 17.0 Fluent module.Drag Coefficient(CD),Lift Coefficient(CL),Drag Force and Lift Force are calculated and compared in different cases.The result of the simulations was analyzed and it was observed that different devices posed several different functionalities,but maximum drag reduction was found in the case of GT with spoiler and diffuser with a maximum reduction of 16.53%.展开更多
The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the oth...The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the other widely used vortexidentification methods such as Q,Δ,λ2,andλci have not been realized.These traditional methods count on shearing and stretching as a part of vortex strength.But,in the real flow,shearing and stretching do not contribute to fluid rotation.In this paper,the decomposition of the velocity gradient tensor is conducted in the Principal Coordinate for uniqueness.Then the contamination effects of stretching and shearing of the traditional methods are investigated and compared with the Liutex method in terms of mathematical analysis and numerical calculations.The results show that the Liutex method is the only method that is not affected by either stretching or shear,as it represents only the local fluid rigid rotation.These results provide supporting evidence that Liutex is the superior method over others.展开更多
How to solve the hypersonic aerothermodynamics around large-scale uncontrolled spacecraft during falling disintegrated process from outer space to earth,is the key to resolve the problems of the uncontrolled Tiangong-...How to solve the hypersonic aerothermodynamics around large-scale uncontrolled spacecraft during falling disintegrated process from outer space to earth,is the key to resolve the problems of the uncontrolled Tiangong-No.1 spacecraft reentry crash.To study aerodynamics of spacecraft reentry covering various flow regimes,a Gas-Kinetic Unified Algorithm(GKUA)has been presented by computable modeling of the collision integral of the Boltzmann equation over tens of years.On this basis,the rotational and vibrational energy modes are considered as the independent variables of the gas molecular velocity distribution function,a kind of Boltzmann model equation involving in internal energy excitation is presented by decomposing the collision term of the Boltzmann equation into elastic and inelastic collision terms.Then,the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions by developing the discrete velocity ordinate method and numerical quadrature technique.The unified algorithm of the Boltzmann model equation involving thermodynamics non-equilibrium effect is presented for the whole range of flow regimes.The gas-kinetic massive parallel computing strategy is developed to solve the hypersonic aerothermodynamics with the processor cores 500~45,000 at least 80%parallel efficiency.To validate the accuracy of the GKUA,the hypersonic flows are simulated including the reentry Tiangong-1 spacecraft shape with the wide range of Knudsen numbers of 220~0.00005 by the comparison of the related results from the DSMC and N-S coupled methods,and the low-density tunnel experiment etc.For uncontrolling spacecraft falling problem,the finite-element algorithm for dynamic thermalforce coupling response is presented,and the unified simulation of the thermal structural response and the hypersonic flow field is tested on the Tiangong-1 shape under reentry aerodynamic environment.Then,the forecasting analysis platform of end-of-life largescale spacecraft flying track is established on the basis of ballistic computation combined with reentry aerothermodynamics and deformation failure/disintegration.展开更多
This paper presents an engineering-oriented UGKS solver package developed in China Aerodynamics Research and Development Center(CARDC).The solver is programmed in Fortran language and uses structured body-fitted mesh,...This paper presents an engineering-oriented UGKS solver package developed in China Aerodynamics Research and Development Center(CARDC).The solver is programmed in Fortran language and uses structured body-fitted mesh,aiming for predicting aerodynamic and aerothermodynamics characteristics in flows covering various regimes on complex three-dimensional configurations.The conservative discrete ordinate method and implicit implementation are incorporated.Meanwhile,a local mesh refinement technique in the velocity space is developed.The parallel strategies include MPI and OpenMP.Test cases include a wedge,a cylinder,a 2D blunt cone,a sphere,and a X38-like vehicle.Good agreements with experimental or DSMC results have been achieved.展开更多
文摘For the general case of a spatial isoenergetic flow of ideal gas,Helmholtz’s theorems are generalized and the speed with which vortex tubes move is found,keeping the intensity.It is shown that along the streamline without stagnation point,vorticity either is equal to zero everywhere,or it is non zero at all.The pattern of vortex lines behind the three-dimensional detached bow shock wave is specified.
基金supported by the National Numerical Windtunnel Project,partially by the National Natural Science Foundation of China under Grant No.61702360.
文摘With the increasing of computing ability,large-scale simulations have been generating massive amounts of data in aerodynamics.Sort-last parallel rendering is the most classical image compositing method for large-scale scientific visualization.However,in the stage of image compositing,the sort-last method may suffer from scalability problem on large-scale processors.Existing image compositing algorithms tend to perform well in certain situations.For instance,Direct Send is well on small and medium scale;Radix-k gets well performance only when the k-value is appropriate and so on.In this paper,we propose a novel method named mSwap for scientific visualization in aerodynamics,which uses the best scale of processors to make sure its performance at the best.mSwap groups the processors that we can use with a(m,k)table,which records the best combination of m(the number of processors in subgroup of each group)and k(the number of processors in each group).Then in each group,using a m-ary tree to composite the image for reducing the communication of processors.Finally,the image is composited between different groups to generate the final image.The performance and scalability of our mSwap method is demonstrated through experiments with thousands of processors.
基金National Numerical Windtunnel Project(No.NNW2019ZT1-A04)National Natural Science Foundation of China(NSFC Grants No.12172161,No.91952104,No.92052301,and No.91752201)+2 种基金Shenzhen Science and Technology Program(Grants No.KQTD20180411143441009)Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(Grant No.GML2019ZD0103)Department of Science and Technology of Guangdong Province(No.2020B1212030001).
文摘A dynamic nonlinear algebraic model with scale-similarity dynamic procedure(DNAM-SSD)is proposed for subgrid-scale(SGS)stress in large-eddy simulation of turbulence.The model coefficients of the DNAM-SSD model are adaptively calculated through the scale-similarity relation,which greatly simplifies the conventional Germano-identity based dynamic procedure(GID).The a priori study shows that the DNAM-SSD model predicts the SGS stress considerably better than the conventional velocity gradient model(VGM),dynamic Smagorinsky model(DSM),dynamic mixed model(DMM)and DNAM-GID model at a variety of filter widths ranging from inertial to viscous ranges.The correlation coefficients of the SGS stress predicted by the DNAM-SSD model can be larger than 95%with the relative errors lower than 30%.In the a posteriori testings of LES,the DNAM-SSD model outperforms the implicit LES(ILES),DSM,DMM and DNAM-GID models without increasing computational costs,which only takes up half the time of the DNAM-GID model.The DNAM-SSD model accurately predicts plenty of turbulent statistics and instantaneous spatial structures in reasonable agreement with the filtered DNS data.These results indicate that the current DNAM-SSD model is attractive for the development of highly accurate SGS models for LES of turbulence.
基金supported by the Open Fund from State Key Laboratory of Aerodynamics of China(Grant No.SKLA20180207)Feng Lei Youth Innovation Fund of CARDC(Grant No.PJD20190003)supported by National Numerical Wind tunnel project(NNW2018-ZT3B08).
文摘At present,the control capability of dielectric barrier discharge(DBD)plasma actuation covers the flow velocity range of helicopter’s retreating blades,so it is necessary to extend it to the dynamic stall control of rotor airfoils.A DBD plasma actuator was adopted to control the dynamic stall of an oscillating CRA309 airfoil in this paper.The effectiveness of alternating current(AC)DBD plasma actuation on reducing the area of lift hysteresis loop of the oscillating airfoil was verified through pressure measurements at a Reynolds number of 5.2×10^(5).The influence of actuation parameters on the airfoil’s lift and moment coefficients was studied.Both steady and unsteady actuation could effectively reduce the hysteresis loop area of the lift coefficients.The flow control effect of dynamic stall was strongly dependent on the history of angle of attack.Compared with the steady actuation,unsteady actuation had more obvious advantages in dynamic stall control,with reducing the area of lift hysteresis loop by more than 30%.The effects of plasma actuation on the airfoil’s flow field at both upward and downward stages were discussed at last.
基金The authors would like to thank the German Research Association for the funding of the project BR 1511/10-1.
文摘A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments.An analysis for three Reynolds numbers is conducted at various angles of attack.The computations are performed by means of the TAU-Code and the FEM Carat++solver.Wind-tunnel tests are carried out for performance analysis and to estimate the accuracy of the computations.In the results,the advantages of an elasto-flexible-lifting-surface concept are highlighted by comparing the formvariable surface to its rigid counterpart.The flexibility of the material and its adaptivity to the freestream allow the membrane to adjust its shape to the pressure distribution.For positive angles of attack,the airfoil’s camber increases resulting in an increase in the wing lifting capacity.Furthermore,the stall onset is postponed to higher angles of attack and the abrupt decrease in the lift is replaced by a gradual loss of it.
基金The second author(A.M.Aly)received financial support from the Louisiana Board of Regents(RCS,LEQSF(2021-22)-RD-A-30)Also,the second author received funds from the NSF I-Corps program at Louisiana State University.The findings are those of the authors and do not necessarily reflect the position of the funding sponsors.
文摘This paper presents an extensive review of existing techniques used in estimating design wind pressures considering Reynolds number and turbulence effects,as well as a case study of a reference building investigated experimentally.We shed light on the limitations of current aerodynamic testing techniques,provisions in design standards,and computational fluid dynamics(CFD)methods to predict wind-induced pressures.The paper highlights the reasons for obstructing the standardization of the wind tunnel method.Moreover,we introduce improved experimental and CFD techniques to tackle the identified challenges.CFD provides superior and efficient performance by employing wall-modeled large-eddy simulation(WMLES)and hybrid RANS-LES models.In addition,we tested a large-scale building model and compared the results with published small-scale data.The findings reinforce our hypothesis concerning the scaling issues and Reynolds number effects in aerodynamic testing.
基金National Numerical Wind Tunnel Project(No.NNW2018-ZT1A03)National Natural Science Foundation of China(No.12072285 and No.11972305).
文摘To increase the efficiency and robustness of stability-based transition prediction in flow simulations, simplified methods are introduced to substitute direct stability analyses for rapid disturbance growth prediction. For low-speed boundary layers, these methods are mainly established based on self-similar assumptions, which are not applicable to non-similar boundary layers in hypersonic flows. The objective of this article is to investigate the application of surrogate models to stability analysis of non-similar flows over blunt cones, focused on parameterization of boundary-layer (BL) profiles. Firstly, correlations between BL edge and profile parameters are analyzed, along with self-similar flow parameters and discrete points on BL profiles, which present four groups of BL characteristic parameters. Secondly, using these parameters as inputs, surrogate models are built for disturbance growth prediction over an MF-1 blunt cone. Results show that, surrogate models using four BL edge parameters and a BL shape factor {Ue, Te, ρe, ηe, H12} for stability analysis can achieve comparable accuracy with those using 16 discrete BL profile parameters, which are more precise than those using merely self-similar parameters or BL edge parameters. Thirdly, the established surrogate models are validated by stability analysis and transition prediction over the MF-1 blunt cone in flight experiments at the instants of t = 17 s ~ 22 s. Compared with direct linear stability analyses, the mean relative error of predicted disturbance growth rates by surrogate models is 8.0% and the maximum relative error of N factor envelopes is 6.6%, which indicates feasible applications of surrogate models to stability analysis and transition prediction of non-similar boundary layers in hypersonic flows.
文摘Despite over fifty years of research on shock wave boundary layer effects and interactions,many related technical issues continue to be controversial and debated.The present survey provides an overview of the present state of knowledge on such effects and interactions,including discussions of:(i)general features of shock wave interactions,(ii)test section configurations for investigation of shock wave boundary layer interactions,(iii)origins and sources of unsteadiness associated with the interaction region,(iv)interactions which included thermal transport and convective heat transfer,and(v)shock wave interaction control investigations.Of particular interest are origins and sources of low-frequency,large-scale shock wave unsteadiness,flow physics of shock wave boundary layer interactions,and overall structure of different types of interactions.Information is also provided in regard to shock wave investigations,where heat transfer and thermal transport were important.Also considered are investigations of shock wave interaction control strategies,which overall,indicate that no single shock wave control strategy is available,which may be successfully applied to different shock wave arrangements,over a wide range of Mach numbers.Overall,the survey highlights the need for additional understanding of fundamental transport mechanisms,as related to shock waves,which are applicable to turbomachinery,aerospace,and aeronautical academic disciplines.
基金National Numerical Windtunnel Project(No.NNW2018-ZT1A02)Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Nanjing University of Aeronautics and Astronautics,No.MCMS-I-0120G01)Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX21-0181).
文摘The combination of Cartesian grid and the adaptive mesh refinement(AMR)technology is an effective way to handle complex geometry and solve complex flow problems.Some high-efficiency Cartesian-based AMR libraries have been developed to handle dynamic changes of the grid in parallel but still can not meet the unique requirements of simulating flow around objects.In this paper,we propose an efficient Cartesian grid generation method and an information transmission approach for the wall boundary to parallelize the implementation of ghost-cell method(GCM).Also,the multi-valued ghost-cell method to handle multi-value points is improved to adapt to the parallel framework.Combining the mentioned methodologies with the open-source library p4est,an automatic and efficient simulation of compressible flow is achieved.The overall performance of the methodology is tested through a wide range of inviscid/viscous flow cases.The results indicate that the capability and parallel scalability of the present numerical methodology for solving multiple types of flows,involving shock and vortices,multi-body flow and unsteady flows are agreeable as compared with related reference data.
文摘Cryogenic wind tunnel is a sophisticated aerodynamics ground test faility,which operates in cryogenic temperature with injection of liquid nitrogen.The multi-variable,nonlinear and coupled dynamics existing between the temperature,pressure and Mach number in the tunnel,poses great challenges for the effective control of the tunnel.L_(1) adaptive control is a new control methodology developed in recent years with good robustness properties,which has good potentials to address these challenges.But this control method does not provide full adaptive feedforward control in its generic structure.In the paper,adaptive feedforward control action is introduced into the standard L_(1) adaptive control architecture for nonlinear systems in the presence of matched un-modeled dynamics.This new control structure is applied to the stagnation pressure control in a cryogenic wind tunnel,which could also be used for the control of temperature and Mach number in the tunnel.This new method could effectively compensate known disturbances with linear gain uncertainty,which occur in the nonlinear systems,while retaining the closed-loop control performance of L_(1) adaptive control.After the proof and discussions on the stability of this method,simulations of the stagnation pressure control in the wind tunnel are presented.The results and analysis demonstrate the effectiveness of the proposed control architecture.
基金National Numerical Windtunnel Project of China(NNW2018ZT2-A04,NNW2020ZT3-A22)National Natural Science Foundation of China(No.51906186).
文摘Prediction of the coupled conduction-radiation heat transfer in composite materials with periodic structure is important in high-temperature applications of the materials. The temperature dependence of thermal properties complicates the problem. In this work, a multiscale model is proposed for the conduction-radiation heat transfer in periodic composite materials with temperature-dependent thermal properties. Homogenization analysis of the coupled conduction and radiative transfer equations is conducted, in which the temperature dependence of thermal properties is considered. Both the macroscopic homogenized equations and the local unit cell problems are derived. It is proved that the macroscopic average temperature can be used in the unit cell problems for the first-order corrections of the temperature and radiative intensity, and the calculations of effective thermal properties. The temperature dependence of thermal properties only influences the higher-order corrections. A multiscale numerical method is proposed based on the analysis. The Gaussian process (GP) regression is coupled into the multiscale algorithm to build a correlation between thermal properties and temperature for the macroscale iterations and prevent the repetitive solving of unit cell problems. The GP model is updated by additional solutions of unit cell problems during the iteration according to a variance threshold. Numerical simulations of conduction-radiation heat transfer in composite with isotropic and anisotropic periodic structures are used to validate the proposed multiscale model. It is found that the accuracy and efficiency of the multiscale method can be guaranteed by using a proper variance threshold for the GP model. The multiscale model can provide both the average temperature and radiative intensity fields and their detailed fluctuations due to the local structures.
基金Natural Science Foundation of Jiangsu Province(Grant No.BK20191271)the National Numerical Wind Tunnel Project(Grant No.NNW2019ZT2-B28).
文摘This paper presents a robust sharp-interface immersed boundary method for simulating inviscid compressible flows over stationary and moving bodies.The flow field is governed by Euler equations,which are solved by using the open source library OpenFOAM.Discontinuities such as those introduced by shock waves are captured by using Kurganov and Tadmor divergence scheme.Wall-slip boundary conditions are enforced at the boundary of body through reconstructing flow variables at some ghost points.Their values are obtained indirectly by interpolating from their mirror points.A bilinear interpolation is employed to determine the variables at the mirror points from boundary conditions and flow conditions around the boundary.To validate the efficiency and accuracy of this method for simulation of high-speed inviscid compressible flows,four cases have been simulated as follows:supersonic flow over a 15°angle wedge,transonic flow past a stationary airfoil,a piston moving with supersonic velocity in a shock tube and a rigid circular cylinder lift-off from a flat surface triggered by a shock wave.Compared to the exact analytical solutions or the results in literature,good agreement can be achieved.
基金Z.L.Guo is supported by the National Natural Science Foundation of China(51836003,11872024)the National Numerical Wind Tunnel project(NNW2019-JT01-016)+1 种基金the Fundamental Research Funds for the Central Universities(2019kfyXMBZ040)K.Xu is supported by the National Natural Science Foundation of China(11772281,91852114).
文摘Multiscale gas flows appear in many fields and have received particular attention in recent years.It is challenging to model and simulate such processes due to the large span of temporal and spatial scales.The discrete unified gas kinetic scheme(DUGKS)is a recently developed numerical approach for simulating multiscale flows based on kinetic models.The finite-volume DUGKS differs from the classical kinetic methods in the modeling of gas evolution and the reconstruction of interface flux.Particularly,the distribution function at a cell interface is reconstructed from the characteristic solution of the kinetic equation in space and time,such that the particle transport and collision effects are coupled,accumulated,and evaluated in a numerical time step scale.Consequently,the cell size and time step of DUGKS are not passively limited by the particle mean-free-path and relaxation time.As a result,the DUGKS can capture the flow behaviors in all regimes without resolving the kinetic scale.Particularly,with the variation of the ratio between numerical mesh size scale and kinetic mean free path scale,the DUGKS can serve as a self-adaptive multiscale method.The DUGKS has been successfully applied to a number of flow problems with multiple flow regimes.This paper presents a brief review of the progress of this method.
基金supported by the National Numerical Wind-tunnel projectThe authors also gratefully acknowledge the financial support of the National Key Research and Development Plan of China through the project No.2019YFA0405201the National Key Project(Grant No.GJXM92579).
文摘The nonlinear analyses of the hypersonic and high-enthalpy boundary-layer transition had received little attention compared with the widely-studied linear instabilities.In this work,the oblique-mode breakdown,as one of the most available transition mechanisms,is studied using the nonlinear parabolized stability equations(NPSE)with consideration of the thermal-chemical non-equilibrium effects.The flow over a blunt cone is computed at a free-stream Mach-number of 15.The rope-like structures and the spontaneous radiation of sound waves are observed in the schlieren-like picture.It is also illustrated that the disturbances of the species mass and vibrational temperature near the wall are mainly generated by the product term of the wall-normal velocity disturbance and the mean-flow gradient.In comparison to the CPG flow,the TCNE effects destabilize the second mode and push upstream the N factor envelope.The higher growth rate of the oblique wave leads to stronger growth of the streamwise vortices and harmonic waves.
基金NNW Project,the Open Project of Science and Technology on Scramjet Laboratory,and the NNSF of China under Grant Number 91952201,11372008,11452002.
文摘The hypersonic boundary layer(HBL)transition on a slender cone at moderate incidence is studied via a symmetry-based length model:the SED-SL model.The SED-SL specifies an analytic stress length function(which defines the eddy viscosity)describing a physically sound two-dimensional multi-regime structure of transitional boundary layer.Previous studies showed accurate predictions,especially on the drag coefficient,by the SED-SL for airfoil flows at different subsonic Mach numbers,Reynolds numbers and angles of attack.Here,the SED-SL is extended to compute the hypersonic heat transfer on a 7∘half-angle straight cone at Mach numbers 6 and 7 and angles of attack from 0∘to 6∘.It is shown that a proper setting of the multi-regime structure with three parameters(i.e.a transition center,an after-transition near-wall eddy length,and a transition width quantifying transition overshoot)yields an accurate description of the surface heat fluxes measured in wind tunnels.Uniformly good agreements between simulations and measurements are obtained from windward to leeward side of the cone,implying the validity of the multi-regime description of the transition independent of instability mechanisms.It is concluded that a unified description for the HBL transition of cone is found,and might offer a basis for developing a new transition model that is simultaneously of computational simplicity,sound physics and greater accuracy.
文摘In this era of fast-depleting natural resources,the hike in fuel prices is ever-growing.With stringent norms over environmental policies,the automotive manufacturers are on a voyage to produce efficient vehicles with lower emissions.High-speed cars are at a stake to provide uncompromised performance but having strict rules over emissions drives the companies to approach through a different route to keep the demands of performance intact.One of the most sought-after ways is to improve the aerodynamics of the vehicles.Drag force is one of the major setbacks when it comes to achieving high speeds when the vehicle is in motion.This research aims to examine the effects of different add on devices on the vehicle to reduce drag and make the vehicle aerodynamically streamlined.A more streamlined vehicle will be able to achieve high speeds and consequently,the fuel economy is also improved.The three-dimensional car model is developed in SOLIDWORKS v17.Computational Fluid Dynamics(CFD)is performed to understand the effects of these add on devices.CFD is carried out in the ANSYS^(TM) 17.0 Fluent module.Drag Coefficient(CD),Lift Coefficient(CL),Drag Force and Lift Force are calculated and compared in different cases.The result of the simulations was analyzed and it was observed that different devices posed several different functionalities,but maximum drag reduction was found in the case of GT with spoiler and diffuser with a maximum reduction of 16.53%.
文摘The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the other widely used vortexidentification methods such as Q,Δ,λ2,andλci have not been realized.These traditional methods count on shearing and stretching as a part of vortex strength.But,in the real flow,shearing and stretching do not contribute to fluid rotation.In this paper,the decomposition of the velocity gradient tensor is conducted in the Principal Coordinate for uniqueness.Then the contamination effects of stretching and shearing of the traditional methods are investigated and compared with the Liutex method in terms of mathematical analysis and numerical calculations.The results show that the Liutex method is the only method that is not affected by either stretching or shear,as it represents only the local fluid rigid rotation.These results provide supporting evidence that Liutex is the superior method over others.
基金The National Key Basic Research and Development Program(2014CB744100)and the National Natural Science Foundation of China(91530319 and 11325212)support the present researches in the design of the study and collection,analysis,and interpretation of data and in writing the manuscript.
文摘How to solve the hypersonic aerothermodynamics around large-scale uncontrolled spacecraft during falling disintegrated process from outer space to earth,is the key to resolve the problems of the uncontrolled Tiangong-No.1 spacecraft reentry crash.To study aerodynamics of spacecraft reentry covering various flow regimes,a Gas-Kinetic Unified Algorithm(GKUA)has been presented by computable modeling of the collision integral of the Boltzmann equation over tens of years.On this basis,the rotational and vibrational energy modes are considered as the independent variables of the gas molecular velocity distribution function,a kind of Boltzmann model equation involving in internal energy excitation is presented by decomposing the collision term of the Boltzmann equation into elastic and inelastic collision terms.Then,the gas-kinetic numerical scheme is constructed to capture the time evolution of the discretized velocity distribution functions by developing the discrete velocity ordinate method and numerical quadrature technique.The unified algorithm of the Boltzmann model equation involving thermodynamics non-equilibrium effect is presented for the whole range of flow regimes.The gas-kinetic massive parallel computing strategy is developed to solve the hypersonic aerothermodynamics with the processor cores 500~45,000 at least 80%parallel efficiency.To validate the accuracy of the GKUA,the hypersonic flows are simulated including the reentry Tiangong-1 spacecraft shape with the wide range of Knudsen numbers of 220~0.00005 by the comparison of the related results from the DSMC and N-S coupled methods,and the low-density tunnel experiment etc.For uncontrolling spacecraft falling problem,the finite-element algorithm for dynamic thermalforce coupling response is presented,and the unified simulation of the thermal structural response and the hypersonic flow field is tested on the Tiangong-1 shape under reentry aerodynamic environment.Then,the forecasting analysis platform of end-of-life largescale spacecraft flying track is established on the basis of ballistic computation combined with reentry aerothermodynamics and deformation failure/disintegration.
基金This work was supported by the National Natural Science Foundation of China(11402287 and 11372342).
文摘This paper presents an engineering-oriented UGKS solver package developed in China Aerodynamics Research and Development Center(CARDC).The solver is programmed in Fortran language and uses structured body-fitted mesh,aiming for predicting aerodynamic and aerothermodynamics characteristics in flows covering various regimes on complex three-dimensional configurations.The conservative discrete ordinate method and implicit implementation are incorporated.Meanwhile,a local mesh refinement technique in the velocity space is developed.The parallel strategies include MPI and OpenMP.Test cases include a wedge,a cylinder,a 2D blunt cone,a sphere,and a X38-like vehicle.Good agreements with experimental or DSMC results have been achieved.
