By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result o...By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result on the global existence and the blow-up phenomena of classical solutions of these systems. These results show that the dissipation is strong enough to preserve the smoothness of ‘small ’ solution.展开更多
The flow around airfoil NACA0012 enwrapped by the body-fitted grid is simulated by a coupled doubledistribution-function （DDF） lattice Boltzmann method （LBM） for the compressible Navier-Stokes equations. Firstly, ...The flow around airfoil NACA0012 enwrapped by the body-fitted grid is simulated by a coupled doubledistribution-function （DDF） lattice Boltzmann method （LBM） for the compressible Navier-Stokes equations. Firstly, the method is tested by simulating the low Reynolds number flow at Ma =0. 5,a=0. 0, Re=5 000. Then the simulation of flow around the airfoil is carried out at Ma：0. 5, 0. 85, 1.2; a=-0.05, 1.0, 0.0, respectively. And a better result is obtained by using a local refined grid. It reduces the error produced by the grid at Ma=0. 85. Though the inviscid boundary condition is used to avoid the problem of flow transition to turbulence at high Reynolds numbers, the pressure distribution obtained by the simulation agrees well with that of the experimental results. Thus, it proves the reliability of the method and shows its potential for the compressible flow simulation. The suecessful application to the flow around airfoil lays a foundation of the numerical simulation of turbulence.展开更多
The noise induced by the fluctuant saturated steam flow under 250 °C in a stop-valve was numerically studied.The simulation was carried out using computational fluid dynamics（CFD） and ACTRAN.The acoustic field ...The noise induced by the fluctuant saturated steam flow under 250 °C in a stop-valve was numerically studied.The simulation was carried out using computational fluid dynamics（CFD） and ACTRAN.The acoustic field was investigated with Lighthill＇s acoustic analogy based on the properties of the flow field obtained using a large-eddy simulation that employs the LES-WALE dynamic model as the sub-grid-scale model.Firstly,the validation of mesh was well conducted,illustrating that two million elements were sufficient in this situation.Secondly,the treatment of the steam was deliberated,and conclusions indicate that when predicting the flow-induced noise of the stop-valve,the steam can be treated as incompressible gas at a low inlet velocity.Thirdly,the flow-induced noises under different inlet velocities were compared.The findings reveal it has remarkable influence on the flow-induced noises.Lastly,whether or not the heat preservation of the wall has influence on the noise was taken into account.The results show that heat preservation of the wall had little influence.展开更多
The analytical solution of a bubble collapse close to a solid boundary in a compressible water is investigated by means of a perturbation method to first order in the bubble wall Mach number. It is shown, in this pape...The analytical solution of a bubble collapse close to a solid boundary in a compressible water is investigated by means of a perturbation method to first order in the bubble wall Mach number. It is shown, in this paper, that it is the Rayleigh?Plesset equation for incompressible liquid to zero order solution or similar to the Gilmore equation for compressible water to first order solution when the effect of solid boundary is negligibly small enough, i.e., sufficiently far away from the bubble center.展开更多
Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces effici...Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces efficient vortex methods developed for high Reynolds number bluff body flows and suitable for running on parallel computer architectures. Included in this study are particle strength exchange methods, core-spreading method, deterministic particle method and hybrid vortex methods. Combined with conservative methods, vortex methods can comprise the most available tools for simulations of three-dimensional complex bluff body flows at high Reynolds numbers.展开更多
Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is ...Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is often calculated from widely used correlation provided in Perry＇s Handbook. This correlation was developed based on experimental work which have covered a wide range of fractional free area （a = 0.14 to 0.79）. The present work aims at validation for a flow in plain square mesh screen with a particular fractional free area （porosity, a） of 0.25 using CFD （Computational Fluid Dynamics） approach. The simulations are carried out for wide range of screen Reynolds number （Re = 0.1 to 105） covering both laminar and turbulent flow regimes. Initial simulations are carried out for incompressible fluid （water） and further extended to compressible fluid （air）. Discharge coefficients obtained from the simulations are compared with experimental values. Effect of compressibility on discharge coefficients is described.展开更多
In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visnalizing density f...In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visnalizing density fields using schlieren method. Numerical calculations were also conducted by solving unsteady three dimensional compressible Navier-Stokes equations with Baldwin-Lomax turbulence model. The main parametm''s for the dual jets are the non-dimensional distance between the two nozzle centers H/D covering 1.5, 2.0, the nozzle to plate separation L/D 2.0, 3.0,4.0 and 5.0 and the pressure ratio defined by Po/Pb 1.0-6.0, where D is the diameter of each nozzle exit, Po the stagnation pressure and Pb the back pressure. It is found that the agreement between the experiments and the calculations is good. The fountain flow at the middle of the two jets is observed both in the experiments and the calculation. According to FFT analysis of the experiments for the twin jets,relatively low frequgncy (up to 5 kHz) is dominant for H/D =1.5, L/D =2.0 and pressure rafio po/Pb =3.0 and 5.0,which is confLrmed by the experiments.展开更多
文摘By means of maximum principle for nonlinear hyperbolic systems, the results given by HSIAO Ling and D. Serre was improved for Cauchy problem of compressible adiabatic flow through porous media, and a complete result on the global existence and the blow-up phenomena of classical solutions of these systems. These results show that the dissipation is strong enough to preserve the smoothness of ‘small ’ solution.
基金Supported by the Aeronautical Science Foundation of China(20061453020)Foundation for Basic Research of Northwestern Polytechnical University(03)~~
文摘The flow around airfoil NACA0012 enwrapped by the body-fitted grid is simulated by a coupled doubledistribution-function （DDF） lattice Boltzmann method （LBM） for the compressible Navier-Stokes equations. Firstly, the method is tested by simulating the low Reynolds number flow at Ma =0. 5,a=0. 0, Re=5 000. Then the simulation of flow around the airfoil is carried out at Ma：0. 5, 0. 85, 1.2; a=-0.05, 1.0, 0.0, respectively. And a better result is obtained by using a local refined grid. It reduces the error produced by the grid at Ma=0. 85. Though the inviscid boundary condition is used to avoid the problem of flow transition to turbulence at high Reynolds numbers, the pressure distribution obtained by the simulation agrees well with that of the experimental results. Thus, it proves the reliability of the method and shows its potential for the compressible flow simulation. The suecessful application to the flow around airfoil lays a foundation of the numerical simulation of turbulence.
文摘The noise induced by the fluctuant saturated steam flow under 250 °C in a stop-valve was numerically studied.The simulation was carried out using computational fluid dynamics（CFD） and ACTRAN.The acoustic field was investigated with Lighthill＇s acoustic analogy based on the properties of the flow field obtained using a large-eddy simulation that employs the LES-WALE dynamic model as the sub-grid-scale model.Firstly,the validation of mesh was well conducted,illustrating that two million elements were sufficient in this situation.Secondly,the treatment of the steam was deliberated,and conclusions indicate that when predicting the flow-induced noise of the stop-valve,the steam can be treated as incompressible gas at a low inlet velocity.Thirdly,the flow-induced noises under different inlet velocities were compared.The findings reveal it has remarkable influence on the flow-induced noises.Lastly,whether or not the heat preservation of the wall has influence on the noise was taken into account.The results show that heat preservation of the wall had little influence.
文摘The analytical solution of a bubble collapse close to a solid boundary in a compressible water is investigated by means of a perturbation method to first order in the bubble wall Mach number. It is shown, in this paper, that it is the Rayleigh?Plesset equation for incompressible liquid to zero order solution or similar to the Gilmore equation for compressible water to first order solution when the effect of solid boundary is negligibly small enough, i.e., sufficiently far away from the bubble center.
基金Project (No. 50236030) supported by the National Natural Science Foundation of China
文摘Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces efficient vortex methods developed for high Reynolds number bluff body flows and suitable for running on parallel computer architectures. Included in this study are particle strength exchange methods, core-spreading method, deterministic particle method and hybrid vortex methods. Combined with conservative methods, vortex methods can comprise the most available tools for simulations of three-dimensional complex bluff body flows at high Reynolds numbers.
文摘Pressure losses in flow components are generally characterized either by pressure loss coefficients or by discharge coefficients. The pressure drop for incompressible flow across a screen of fractional free area a is often calculated from widely used correlation provided in Perry＇s Handbook. This correlation was developed based on experimental work which have covered a wide range of fractional free area （a = 0.14 to 0.79）. The present work aims at validation for a flow in plain square mesh screen with a particular fractional free area （porosity, a） of 0.25 using CFD （Computational Fluid Dynamics） approach. The simulations are carried out for wide range of screen Reynolds number （Re = 0.1 to 105） covering both laminar and turbulent flow regimes. Initial simulations are carried out for incompressible fluid （water） and further extended to compressible fluid （air）. Discharge coefficients obtained from the simulations are compared with experimental values. Effect of compressibility on discharge coefficients is described.
文摘In this paper, the dual underexpanded impinging jets are experimentally and numerically studied. The experiments were performed by measuring the unsteady and averaged wall static pressures and by visnalizing density fields using schlieren method. Numerical calculations were also conducted by solving unsteady three dimensional compressible Navier-Stokes equations with Baldwin-Lomax turbulence model. The main parametm''s for the dual jets are the non-dimensional distance between the two nozzle centers H/D covering 1.5, 2.0, the nozzle to plate separation L/D 2.0, 3.0,4.0 and 5.0 and the pressure ratio defined by Po/Pb 1.0-6.0, where D is the diameter of each nozzle exit, Po the stagnation pressure and Pb the back pressure. It is found that the agreement between the experiments and the calculations is good. The fountain flow at the middle of the two jets is observed both in the experiments and the calculation. According to FFT analysis of the experiments for the twin jets,relatively low frequgncy (up to 5 kHz) is dominant for H/D =1.5, L/D =2.0 and pressure rafio po/Pb =3.0 and 5.0,which is confLrmed by the experiments.
