A method based on decomposition of acceleration field and Lie derivative is introduced to identify shearing and rotational domains.This method is validated on two typical kinds of model flows.Vorticity dynamics of flo...A method based on decomposition of acceleration field and Lie derivative is introduced to identify shearing and rotational domains.This method is validated on two typical kinds of model flows.Vorticity dynamics of flow around bluff body is studied,illustrated by numerical examples of flow around an elliptic cylinder,a slanted elliptic cylinder and an elliptic cylinder with a pair of bumps on the front side.To explain the generation of vortical structures and how they evolve into inner flow field,boundary vorticity dynamics analysis is performed.Boundary vorticity flux as well as the enstrophy diffusion flux creates vorticity sources and vorticity sinks,which generate or consume boundary vorticity,then shearing layers are generated and interact with each other finally create vortices.The results provide potential in accurate flow control by boundary deformation,and show that relevant theoretical conclusions can be effectively applied in revealing the flow mechanisms.展开更多
In this paper,by applying theoretical method to the governing equations of compressible viscous flow,we derive the theoretical formula of the boundary dilatation flux(BDF)on a flexible wall,which generalizes the most ...In this paper,by applying theoretical method to the governing equations of compressible viscous flow,we derive the theoretical formula of the boundary dilatation flux(BDF)on a flexible wall,which generalizes the most recent work of Mao et al.(Acta Mechanica Sinica 38(2022)321583)for a stationary wall.Different boundary sources of dilatation are explicitly identified,revealing not only the boundary generation mechanisms of vortex sound and entropy sound,but also some additional sources due to the surface vorticity,surface angular velocity,surface acceleration and surface curvature.In particular,the generation mechanism of dilatation at boundary due to the coupled divergence terms is highlighted,namely,the product of the surface velocity divergence(▽_(■B)·U)and the vorticity-induced skin friction divergence(V_(■B)·τ_(ω)).The former is attributed to the surface flexibility while the latter characterizes the footprints of near-wall coherent structures.Therefore,by properly designing the surface velocity distribution,the dilatation generation at the boundary could be controlled for practical purpose in near-wall compressible viscous flows.展开更多
Why the stall of an airfoil can be significantly delayed by its pitching-up motion？ Various attempts have been proposed to answer this question over the past half century, but none is satisfactory. In this letter we ...Why the stall of an airfoil can be significantly delayed by its pitching-up motion？ Various attempts have been proposed to answer this question over the past half century, but none is satisfactory. In this letter we prove that a chain of vorticity-dynamics processes at accelerating boundary is fully responsible for the causal mechanism underlying this peculiar phenomenon. The local flow behavior is explained by a simple potential-flow model.展开更多
基金the National Nature Science Foundation of China(Grant Nos.11472082,11172069).
文摘A method based on decomposition of acceleration field and Lie derivative is introduced to identify shearing and rotational domains.This method is validated on two typical kinds of model flows.Vorticity dynamics of flow around bluff body is studied,illustrated by numerical examples of flow around an elliptic cylinder,a slanted elliptic cylinder and an elliptic cylinder with a pair of bumps on the front side.To explain the generation of vortical structures and how they evolve into inner flow field,boundary vorticity dynamics analysis is performed.Boundary vorticity flux as well as the enstrophy diffusion flux creates vorticity sources and vorticity sinks,which generate or consume boundary vorticity,then shearing layers are generated and interact with each other finally create vortices.The results provide potential in accurate flow control by boundary deformation,and show that relevant theoretical conclusions can be effectively applied in revealing the flow mechanisms.
文摘In this paper,by applying theoretical method to the governing equations of compressible viscous flow,we derive the theoretical formula of the boundary dilatation flux(BDF)on a flexible wall,which generalizes the most recent work of Mao et al.(Acta Mechanica Sinica 38(2022)321583)for a stationary wall.Different boundary sources of dilatation are explicitly identified,revealing not only the boundary generation mechanisms of vortex sound and entropy sound,but also some additional sources due to the surface vorticity,surface angular velocity,surface acceleration and surface curvature.In particular,the generation mechanism of dilatation at boundary due to the coupled divergence terms is highlighted,namely,the product of the surface velocity divergence(▽_(■B)·U)and the vorticity-induced skin friction divergence(V_(■B)·τ_(ω)).The former is attributed to the surface flexibility while the latter characterizes the footprints of near-wall coherent structures.Therefore,by properly designing the surface velocity distribution,the dilatation generation at the boundary could be controlled for practical purpose in near-wall compressible viscous flows.
基金supported by the National Natural Science Foundation of China(10921202,11221062,11521091,and 11472016)
文摘Why the stall of an airfoil can be significantly delayed by its pitching-up motion？ Various attempts have been proposed to answer this question over the past half century, but none is satisfactory. In this letter we prove that a chain of vorticity-dynamics processes at accelerating boundary is fully responsible for the causal mechanism underlying this peculiar phenomenon. The local flow behavior is explained by a simple potential-flow model.
