Large eddy simulation (LES) explicitly calculates the large-scale vortex field and parameterizes the small-scale vortices.In this study,LES and κ-ε models were developed for a specific geometrical configuration of b...Large eddy simulation (LES) explicitly calculates the large-scale vortex field and parameterizes the small-scale vortices.In this study,LES and κ-ε models were developed for a specific geometrical configuration of backward-facing step (BFS).The simulation results were validated with particle image velocimetry (PIV) measurements and direct numerical simulation (DNS).This LES simulation was carried out with a Reynolds number of 9000 in a pressurized water tunnel with an expansion ratio of 2.00.The results indicate that the LES model can reveal largescale vortex motion although with a larger grid-cell size.However,the LES model tends to overestimate the top wall separation and the Reynolds stress components for the BFS flow simulation without a sufficiently fine grid.Overall,LES is a potential tool for simulating separated flow controlled by large-scale vortices.展开更多
The flow over a backward-facing step(BFS)is a typical separation and reattachment flow.Its flow structures and unsteady mechanisms are still not well explored.In this paper,the global velocity fields of a BFS are obta...The flow over a backward-facing step(BFS)is a typical separation and reattachment flow.Its flow structures and unsteady mechanisms are still not well explored.In this paper,the global velocity fields of a BFS are obtained by a synchronous particle image velocimetry(PIV)system with Reh=5345(Reynolds number)and Er=2(expansion ratio).Flow structures are distinguished and defined by the fraction of the negative velocity(upn).The reattachment zone(Lr)is quantitatively defined as(u0.9,u/0.1)on the bottom wall.Spatial distribution of the large-scale vortices couples well with the divided flow structures and their temporal evolution presenting four stages(forming,developing,shedding and redeveloping)when travel downstream.The unsteady motions with various low frequencies are well explained by the coherent vortices and flow structures.Among the unsteady low frequency motions,the Kelvin Helmholtz(KH)vortices and the oscillation of Xr(OX)come likely from the free shear layer.The KH vortices contribute to the unsteadiness of the temporal flow,and the OX is the primary response to the vortical fluctuations.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51379128)
文摘Large eddy simulation (LES) explicitly calculates the large-scale vortex field and parameterizes the small-scale vortices.In this study,LES and κ-ε models were developed for a specific geometrical configuration of backward-facing step (BFS).The simulation results were validated with particle image velocimetry (PIV) measurements and direct numerical simulation (DNS).This LES simulation was carried out with a Reynolds number of 9000 in a pressurized water tunnel with an expansion ratio of 2.00.The results indicate that the LES model can reveal largescale vortex motion although with a larger grid-cell size.However,the LES model tends to overestimate the top wall separation and the Reynolds stress components for the BFS flow simulation without a sufficiently fine grid.Overall,LES is a potential tool for simulating separated flow controlled by large-scale vortices.
基金Project supported by the National Natural Science Foundation of China(Grant No.51909169)The Science and Technology Support Program of Jiangsu Province(Grant No.SBK2019042181)+1 种基金the Guizhou Science and Technology Cooperation Support((2017)2865)the International S&T Cooperation Program of China(Grant No.2015DFA01000).
文摘The flow over a backward-facing step(BFS)is a typical separation and reattachment flow.Its flow structures and unsteady mechanisms are still not well explored.In this paper,the global velocity fields of a BFS are obtained by a synchronous particle image velocimetry(PIV)system with Reh=5345(Reynolds number)and Er=2(expansion ratio).Flow structures are distinguished and defined by the fraction of the negative velocity(upn).The reattachment zone(Lr)is quantitatively defined as(u0.9,u/0.1)on the bottom wall.Spatial distribution of the large-scale vortices couples well with the divided flow structures and their temporal evolution presenting four stages(forming,developing,shedding and redeveloping)when travel downstream.The unsteady motions with various low frequencies are well explained by the coherent vortices and flow structures.Among the unsteady low frequency motions,the Kelvin Helmholtz(KH)vortices and the oscillation of Xr(OX)come likely from the free shear layer.The KH vortices contribute to the unsteadiness of the temporal flow,and the OX is the primary response to the vortical fluctuations.
