To address the early separation problem in the Menter Shear-Stress Transport(SST)turbulence model,a correction for the Turbulent Kinetic Energy(TKE)production term,P_(k),is introduced to account for the effect of the ...To address the early separation problem in the Menter Shear-Stress Transport(SST)turbulence model,a correction for the Turbulent Kinetic Energy(TKE)production term,P_(k),is introduced to account for the effect of the Adverse Pressure Gradient(APG).The correction is determined based on the distribution of Pkin the APG region before separation.When the friction coefficient C_(f) is decomposed,its direct dependence on Pkis clearly observed.However,with the introduction of Bradshaw’s assumption,Pkin the SST turbulence model is over-suppressed,resulting in a lower inner peak or no significant inner peak distribution at all.To address this problem,this paper proposes a Gaussian function,HGauss,which corrects the numerical values of P_(k) involved in the calculation of the Menter SST model by focusing on the inner peak region of P_(k).The modified SST model is then applied to four cases with APGs.The modification leads to an increase in the wall friction coefficient C_(f)in the APG region and causes a downstream shift in the separation location,improving the model’s consistency with high-accuracy data and experimental results.It is demonstrated that this correction can improve the early separation problem in the Menter SST turbulence model.展开更多
Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,90...Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS （URANS）. Some typical linear and nonlinear eddy viscosity turbulence models （LEVM and NLEVM） and a quadratic explicit algebraic stress model （EASM） are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.展开更多
Detailed formulation of the detached-eddy simulation （DES） based on shear stress transport model （SST） was deduced. Based on finite volume method, detached-eddy simulation of super- sonic turbulent flow over rearw...Detailed formulation of the detached-eddy simulation （DES） based on shear stress transport model （SST） was deduced. Based on finite volume method, detached-eddy simulation of super- sonic turbulent flow over rearward facing step was conducted. Multi-block structured non-conform grid was designed. The obtained distribution of wall pressure coefficient along the downstream of the step was in good agreement with experiment. The structure of supersonic flow over rearward facing step is complicated and contains boundary layer-shock interaction, shock-shock interaction and sec- ondary flow separation. The predictions of the corner pressure and location of the reattachment shock are more exact than the Reynolds-averaged method. Results show that detached-eddy simulation can simulate the supersonic separated flows exactly and has advantages over Reynolds-averaged method. The partition of the detached-eddy simulation can be easily achieved by using multi-block non-conform grid, which reduces the requirement of the computational resources as well.展开更多
The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence mode...The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles,is employed. With considering the effect of gravity, interfacial lift, inter-phase friction, virtualmass force and interfacial pressure on the flow with microbubbles, numerical calculations for theinfluence of variable air volume fracton as well as distribution, injecting speed, microbubblediameter and position of introducing microbubbles on the friction reduction are presented. Resultsshow that the friction reduction increases with increasing volume fraction and microbubble diameterwithin the range of 100μm, and that the velocity in the boundary layer with microbubbles is greaterthan that without microbubbles. The order of magnitude and trends of the experimental skin-frictionare reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number ofup to 20 million.展开更多
In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the...In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the threedimensional cavitating flow.The governing equations of the two-phase cavitating flow are derived from the kinetic theory based on the Boltzmann equation.The isotropic RNG k−ε−kca turbulence model of two-phase flows in the form of cavity number instead of the formof cavity phase volume fraction is developed.The RNG k−ε−kca turbulence model,that is the RNG k−εturbulence model for the liquid phase combined with the kca model for the cavity phase,is employed to close the governing turbulent equations of the two-phase flow.The computation of the cavitating flow through a model pump sump has been carried out with this model in three-dimensional spaces.The calculated results have been compared with the data of the PIV experiment.Good qualitative agreement has been achievedwhich exhibits the reliability of the numerical simulation model.展开更多
基金supported by the National Natural Science Foundation of China(No.92252201)。
文摘To address the early separation problem in the Menter Shear-Stress Transport(SST)turbulence model,a correction for the Turbulent Kinetic Energy(TKE)production term,P_(k),is introduced to account for the effect of the Adverse Pressure Gradient(APG).The correction is determined based on the distribution of Pkin the APG region before separation.When the friction coefficient C_(f) is decomposed,its direct dependence on Pkis clearly observed.However,with the introduction of Bradshaw’s assumption,Pkin the SST turbulence model is over-suppressed,resulting in a lower inner peak or no significant inner peak distribution at all.To address this problem,this paper proposes a Gaussian function,HGauss,which corrects the numerical values of P_(k) involved in the calculation of the Menter SST model by focusing on the inner peak region of P_(k).The modified SST model is then applied to four cases with APGs.The modification leads to an increase in the wall friction coefficient C_(f)in the APG region and causes a downstream shift in the separation location,improving the model’s consistency with high-accuracy data and experimental results.It is demonstrated that this correction can improve the early separation problem in the Menter SST turbulence model.
文摘Accurate prediction of unsteady separated turbulent flows remains one of the toughest tasks and a practi cal challenge for turbulence modeling. In this paper, a 2D flow past a circular cylinder at Reynolds number 3,900 is numerically investigated by using the technique of unsteady RANS （URANS）. Some typical linear and nonlinear eddy viscosity turbulence models （LEVM and NLEVM） and a quadratic explicit algebraic stress model （EASM） are evaluated. Numerical results have shown that a high-performance cubic NLEVM, such as CLS, are superior to the others in simulating turbulent separated flows with unsteady vortex shedding.
文摘Detailed formulation of the detached-eddy simulation （DES） based on shear stress transport model （SST） was deduced. Based on finite volume method, detached-eddy simulation of super- sonic turbulent flow over rearward facing step was conducted. Multi-block structured non-conform grid was designed. The obtained distribution of wall pressure coefficient along the downstream of the step was in good agreement with experiment. The structure of supersonic flow over rearward facing step is complicated and contains boundary layer-shock interaction, shock-shock interaction and sec- ondary flow separation. The predictions of the corner pressure and location of the reattachment shock are more exact than the Reynolds-averaged method. Results show that detached-eddy simulation can simulate the supersonic separated flows exactly and has advantages over Reynolds-averaged method. The partition of the detached-eddy simulation can be easily achieved by using multi-block non-conform grid, which reduces the requirement of the computational resources as well.
文摘The two-dimensional flow on the flat plate with injected microbubbles issimulated using the software, PHOENICS (V3. 2), usually used in the CFD (Computational FluidDynamics). A set of formulas for K-ε turbulence model modified with the presence of microbubbles,is employed. With considering the effect of gravity, interfacial lift, inter-phase friction, virtualmass force and interfacial pressure on the flow with microbubbles, numerical calculations for theinfluence of variable air volume fracton as well as distribution, injecting speed, microbubblediameter and position of introducing microbubbles on the friction reduction are presented. Resultsshow that the friction reduction increases with increasing volume fraction and microbubble diameterwithin the range of 100μm, and that the velocity in the boundary layer with microbubbles is greaterthan that without microbubbles. The order of magnitude and trends of the experimental skin-frictionare reproduced well. The uniform free-stream speed in all cases is 4m/s, giving Reynolds number ofup to 20 million.
基金This research work was funded by the Chinese National Foundation of Natural Science(Nos.51076077,51176168,51249003 and 51076144)This work is also supported by Science Foundation of Zhejiang Sci-Tech University(ZSTU) under Grant No.11130032241201.
文摘In the present work,both computational and experimentalmethods are employed to study the two-phase flow occurring in a model pump sump.The twofluid model of the two-phase flow has been applied to the simulation of the threedimensional cavitating flow.The governing equations of the two-phase cavitating flow are derived from the kinetic theory based on the Boltzmann equation.The isotropic RNG k−ε−kca turbulence model of two-phase flows in the form of cavity number instead of the formof cavity phase volume fraction is developed.The RNG k−ε−kca turbulence model,that is the RNG k−εturbulence model for the liquid phase combined with the kca model for the cavity phase,is employed to close the governing turbulent equations of the two-phase flow.The computation of the cavitating flow through a model pump sump has been carried out with this model in three-dimensional spaces.The calculated results have been compared with the data of the PIV experiment.Good qualitative agreement has been achievedwhich exhibits the reliability of the numerical simulation model.
