A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the c...A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.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
This paper describes the design of a new kind of miniature abrading sphere, which is magnetically mounted inside a spherical gap and set in rotation pneumatically with air. Large eddy simulation is performed in conjun...This paper describes the design of a new kind of miniature abrading sphere, which is magnetically mounted inside a spherical gap and set in rotation pneumatically with air. Large eddy simulation is performed in conjunction with the compressible Smagorinsky model. Minimal temperature variation allows for the assumption of adiabatic walls. Fluid-solid interaction is modeled using the law of the wall for compressible turbulent flow. A parametric study is done to determine optimal geometric layout while taking physical restrictions into account. The resulting optimal configuration is then examined in detail in order to determine demands to be met by the computerized control of the magnetic bearing as well as to quantify the force available to the abrasion process. Finally, a mathematical relation is given that determines available abrasion force depending on standard volumetric flow rate and rotation frequency. The findings presented here provide a basis for further development of smaller versions of the tool.展开更多
We take the two dimensional vorticity equations as models to describe spectral methods and their combinations with finite difference methods or finite element methods, which are applicable to other similar nonlinear ...We take the two dimensional vorticity equations as models to describe spectral methods and their combinations with finite difference methods or finite element methods, which are applicable to other similar nonlinear problems. Some numerical results and error estimates of these methods are given.展开更多
The large eddy simulation (LES) of compressible turbulent channel flows at three different Mach numbers is performed in the present work,by extending the dynamic mixed subgrid-scale (SGS) model to compressible flows.T...The large eddy simulation (LES) of compressible turbulent channel flows at three different Mach numbers is performed in the present work,by extending the dynamic mixed subgrid-scale (SGS) model to compressible flows.The turbulent statistics agree well with those from the existing direct numerical simulation (DNS) results,indicating that the LES method established in the present work is reliable.The analysis of the turbulent fluctuations computed by the present LES reveals that the flows considered in this work follow the Morkovin's hypothesis.Thus,the compressibility effects are dominated by the mean field properties,and the relevant statistical ratios are invariant to the variation of Mach number.The near-wall streamwise streaks are more coherent and the spacing between streaks is wider as the Mach number increases.This can be regarded as a direct feature characterized by the compressibility effects.The restrained influences of compressibility effects on the production and dissipation of the turbulence kinetic energy are also identified based on the present LES results.展开更多
In the last few years intensive experimental investigations were performed at the University of Karlsruhe to develop an analytical model for the Helmholtz resonator-type combustion system. In the present work the reso...In the last few years intensive experimental investigations were performed at the University of Karlsruhe to develop an analytical model for the Helmholtz resonator-type combustion system. In the present work the resonance characteristics of a Helmholtz resonator-type combustion chamber were investigated using large-eddy simulations (LES), to understand better the flow effects in the chamber and to localize the dissipation. In this paper the results of the LES are presented, which show good agreement with the experiments. The comparison of the LES study with the experiments sheds light on the significant role of the wall roughness in the exhaust gas pipe.展开更多
The contribution deals with the experimental and numerical investigation of compressible flow through the tip-section turbine blade cascade with the blade 54″ long. Experimental investigations by means of optical(int...The contribution deals with the experimental and numerical investigation of compressible flow through the tip-section turbine blade cascade with the blade 54″ long. Experimental investigations by means of optical(interferometry and schlieren method) and pneumatic measurements provide more information about the behaviour and nature of basic phenomena occurring in the profile cascade flow field. The numerical simulation was carried out by means of the EARSM turbulence model according to Hellsten [5] completed by the bypass transition model with the algebraic equation for the intermittency coefficient proposed by Straka and P?íhoda [6] and implemented into the in-house numerical code. The investigation was focused particularly on the effect of shock waves on the shear layer development including the laminar/turbulent transition. Interactions of shock waves with shear layers on both sides of the blade result usually in the transition in attached and/ or separated flow and so to the considerable impact to the flow structure and energy losses in the blade cascade.展开更多
In this paper, energy separation effect in a vortex tube has been investigated using a CFD model. Thenumerical simulation has been done due to the complex structure of flow. The governing equationshave been solved by ...In this paper, energy separation effect in a vortex tube has been investigated using a CFD model. Thenumerical simulation has been done due to the complex structure of flow. The governing equationshave been solved by FLUENT code in 2D and 3D compressible and turbulent model. The effects ofgeometrical and thermo-physical parameters have been investigated. The results have shown that theoptimum length to diameter ratio is from 25 to 35. Increasing the number of nozzles from 2 to 4 withconvergent shape is found to be an efficient configuration for the swirl generator. The optimum valueof orifice diameter to tube diameter ratio, for the maximum cold air temperature difference and efficiency,has been determined to be around 0.58. The results show that if the inlet pressure increases upto a critical value, the efficiency will increase. Nevertheless, if it increases to higher values, the efficiencywill decrease. Moreover, it is found out that increasing the cold fraction decreases the coldtemperature difference and efficiency.展开更多
A time marching algorithms, which is used to solve incompressible internal flow fields in turbomachinery, has beendeveloped. By using Chorin’s method of artificial compressibility, the governing equations are transfo...A time marching algorithms, which is used to solve incompressible internal flow fields in turbomachinery, has beendeveloped. By using Chorin’s method of artificial compressibility, the governing equations are transformed fromelliptic type into hyperbolic form in order to extend the time marching technique to very low Mach number flows.Viscous effects can be predicted by using the distributed body force method and Baldwin-Lomax eddy viscosityturbulence model. Some accelerating convergence techniques such as multi-grid and local time step method areemployed. The applicahon to a flow field within a low-solidity rocket pump inducer is presented and discussed.展开更多
Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(...Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.展开更多
The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to ...The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand the detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee''s total variation diminishing (TVD) scheme is used to solve the unsteady two-dimensional compressible Euler equations. The Mach number Ms of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two-parallel tubes, the peak pressure produced by the twin impulse waves and its location strongly depend upon the distance between two-parallel tubes, L/d and the incident shock Mach number, Ms. The predicted Schlieren images represent the measured twin-impulse wave with a good accuracy.展开更多
基金Supported by the National Science Foundation for Post-doctoral Scientists of China(20100481141,201104567)the Natural Science Foundation of Jiangsu Province(BK2011723)the Planned Projects for Postdoctoral Research Foundation of Jiangsu Province(0902001C)~~
文摘A hybrid central-upwind scheme is proposed. Two sub-schemes, the central difference scheme and the Roets flux difference splitting scheme, are hybridized by means of a binary sensor function. In order to examine the capability of the proposed hybrid scheme in computing compressible turbulent flow around a curved surface body, especially the flow involving shock wave, three typical eases are investigated by using detached-eddy simulation technique. Numerical results show good agreements with the experimental measurements. The present hybrid scheme can be applied to simulating the compressible flow around a curved surface body involving shock wave and turbulence.
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This paper describes the design of a new kind of miniature abrading sphere, which is magnetically mounted inside a spherical gap and set in rotation pneumatically with air. Large eddy simulation is performed in conjunction with the compressible Smagorinsky model. Minimal temperature variation allows for the assumption of adiabatic walls. Fluid-solid interaction is modeled using the law of the wall for compressible turbulent flow. A parametric study is done to determine optimal geometric layout while taking physical restrictions into account. The resulting optimal configuration is then examined in detail in order to determine demands to be met by the computerized control of the magnetic bearing as well as to quantify the force available to the abrasion process. Finally, a mathematical relation is given that determines available abrasion force depending on standard volumetric flow rate and rotation frequency. The findings presented here provide a basis for further development of smaller versions of the tool.
文摘We take the two dimensional vorticity equations as models to describe spectral methods and their combinations with finite difference methods or finite element methods, which are applicable to other similar nonlinear problems. Some numerical results and error estimates of these methods are given.
文摘The large eddy simulation (LES) of compressible turbulent channel flows at three different Mach numbers is performed in the present work,by extending the dynamic mixed subgrid-scale (SGS) model to compressible flows.The turbulent statistics agree well with those from the existing direct numerical simulation (DNS) results,indicating that the LES method established in the present work is reliable.The analysis of the turbulent fluctuations computed by the present LES reveals that the flows considered in this work follow the Morkovin's hypothesis.Thus,the compressibility effects are dominated by the mean field properties,and the relevant statistical ratios are invariant to the variation of Mach number.The near-wall streamwise streaks are more coherent and the spacing between streaks is wider as the Mach number increases.This can be regarded as a direct feature characterized by the compressibility effects.The restrained influences of compressibility effects on the production and dissipation of the turbulence kinetic energy are also identified based on the present LES results.
文摘In the last few years intensive experimental investigations were performed at the University of Karlsruhe to develop an analytical model for the Helmholtz resonator-type combustion system. In the present work the resonance characteristics of a Helmholtz resonator-type combustion chamber were investigated using large-eddy simulations (LES), to understand better the flow effects in the chamber and to localize the dissipation. In this paper the results of the LES are presented, which show good agreement with the experiments. The comparison of the LES study with the experiments sheds light on the significant role of the wall roughness in the exhaust gas pipe.
基金supported by the Technology Agency of the Czech Republic under the grant TA03020277by the Czech Science Foundation under grant P101/12/1271
文摘The contribution deals with the experimental and numerical investigation of compressible flow through the tip-section turbine blade cascade with the blade 54″ long. Experimental investigations by means of optical(interferometry and schlieren method) and pneumatic measurements provide more information about the behaviour and nature of basic phenomena occurring in the profile cascade flow field. The numerical simulation was carried out by means of the EARSM turbulence model according to Hellsten [5] completed by the bypass transition model with the algebraic equation for the intermittency coefficient proposed by Straka and P?íhoda [6] and implemented into the in-house numerical code. The investigation was focused particularly on the effect of shock waves on the shear layer development including the laminar/turbulent transition. Interactions of shock waves with shear layers on both sides of the blade result usually in the transition in attached and/ or separated flow and so to the considerable impact to the flow structure and energy losses in the blade cascade.
文摘In this paper, energy separation effect in a vortex tube has been investigated using a CFD model. Thenumerical simulation has been done due to the complex structure of flow. The governing equationshave been solved by FLUENT code in 2D and 3D compressible and turbulent model. The effects ofgeometrical and thermo-physical parameters have been investigated. The results have shown that theoptimum length to diameter ratio is from 25 to 35. Increasing the number of nozzles from 2 to 4 withconvergent shape is found to be an efficient configuration for the swirl generator. The optimum valueof orifice diameter to tube diameter ratio, for the maximum cold air temperature difference and efficiency,has been determined to be around 0.58. The results show that if the inlet pressure increases upto a critical value, the efficiency will increase. Nevertheless, if it increases to higher values, the efficiencywill decrease. Moreover, it is found out that increasing the cold fraction decreases the coldtemperature difference and efficiency.
文摘A time marching algorithms, which is used to solve incompressible internal flow fields in turbomachinery, has beendeveloped. By using Chorin’s method of artificial compressibility, the governing equations are transformed fromelliptic type into hyperbolic form in order to extend the time marching technique to very low Mach number flows.Viscous effects can be predicted by using the distributed body force method and Baldwin-Lomax eddy viscosityturbulence model. Some accelerating convergence techniques such as multi-grid and local time step method areemployed. The applicahon to a flow field within a low-solidity rocket pump inducer is presented and discussed.
基金supported by the National Nature Science Foundation of China (Grant Nos.90716008,10572004 and 11172006)the National Basic Research Program of China (Grant No.2009CB724100)
文摘Classical Mach-number(M) scaling in compressible wall turbulence was suggested by van Driest(Van Driest E R.Turbulent boundary layers in compressible fluids.J Aerodynamics Science,1951,18(3):145-160) and Huang et al.(Huang P G,Coleman G N,Bradshaw P.Compressible turbulent channel flows:DNS results and modeling.J Fluid Mech,1995,305:185-218).Using a concept of velocity-vorticity correlation structure(VVCS),defined by high correlation regions in a field of two-point cross-correlation coefficient between a velocity and a vorticity component,we have discovered a limiting VVCS as the closest streamwise vortex structure to the wall,which provides a concrete Morkovin scaling summarizing all compressibility effects.Specifically,when the height and mean velocity of the limiting VVCS are used as the units for the length scale and the velocity,all geometrical measures in the spanwise and normal directions,as well as the mean velocity and fluctuation(r.m.s) profiles become M-independent.The results are validated by direct numerical simulations(DNS) of compressible channel flows with M up to 3.Furthermore,a quantitative model is found for the M-scaling in terms of the wall density,which is also validated by the DNS data.These findings yield a geometrical interpretation of the semi-local transformation(Huang et al.,1995),and a conclusion that the location and the thermodynamic properties associated with the limiting VVCS determine the M-effects on supersonic wall-bounded flows.
文摘The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand the detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee''s total variation diminishing (TVD) scheme is used to solve the unsteady two-dimensional compressible Euler equations. The Mach number Ms of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two-parallel tubes, the peak pressure produced by the twin impulse waves and its location strongly depend upon the distance between two-parallel tubes, L/d and the incident shock Mach number, Ms. The predicted Schlieren images represent the measured twin-impulse wave with a good accuracy.
