Relaxation Features of a Turbulent Boundary Layer in an Unfavorable Pressure Gradient

摘要

The relaxation of a shear flow (the process of an equilibrium state recovery) caused by the presence of a disturbance source such as a wall fence roughness elements or obstacle in a turbulent boundary layer is a slow process which can not be predicted at least accurately even on the basis of current turbulence models. Previous investigations are devoted to the study of the process of the boundary-layer relaxation under the conditions of gradient-free streamwise flow. However the majority of practical cases which deal for example, with the development of optimum design of heat exchanger channels, of elements and units of airspace technology, is related to the class of nonequilibrium (by Clauser) flows forming in unfavorable pressure gradient. To the authors knowledge, paper is the only which is actually devoted to the study of the turbulent boundary layer relaxation under the conditions of unfavorable pressure gradient for the case of flow around a obstacle of height h. Nearby the equilibrium state has not been reached right up to the last measuring cross section. It is quite evident that the studying in the conditions mentioned above of the behavior of a nonequilibrium turbulent boundary layer disturbed by the presence of a source of any geometry, is more actual problem.