Wärme‐, Stoff‐ und Impulsübertragung in abgelösten Strömungen

Abstract

AbstractHeat, mass and momentum transfer in separated flows. The simple model of a backward‐facing step in flat plate boundary layers provides basic information on heat, mass and momentum transfer in local separated regions. These new investigations cover nearly the whole range of existence of incompressible separated flows with laminar as well as turbulent boundary layers at separation, including the two main parameters Reδ1 and Res: The Reynolds number Reδ1 represents the boundary layer at separation, the Reynolds number Res the shape of the body. It is demonstrated that independently of the state of the boundary layer at separation, there exist three types of local separated regions. Therefore a new general valid classification of local separated flows is introduced based on the actual state of the separated boundary (shear) layer from separation to reattachement. The new results presented are limited to the case where no temperature or concentration boundary layers exist at separation, i.e. to the case of unheated or inert starting length before separation: Only then can the analogy of heat, mass and momentum transfer give useful results over the whole range of existence of local separated regions. A new shear layer model is introduced to facilitate transfer of the results obtained for backward‐facing steps to arbitrary shaped bodies. A compilation and comparison of available literature values shows that this shear layer model for the step also permits the calculation of heat and mass transfer in separated areas on arbitrarily shaped bodies.