Energy Separation in Steady Separated Wake Flow

Abstract

The phenomenon that regions of different total enthalpy can develop in an external flow starting from initially homogeneous conditions upstream is known as “energy separation.” Eckert (1-2) discussed its basic mechanisms and introduced the energy separation factor S=(H−He)∕12ue2 as descriptive nondimensional parameter. In inviscid flow the only mechanism for energy redistribution is unsteady pressure work and strong energy separation has indeed been observed for a number of unsteady flow phenomena, notably the vortex wake (3-5). Several studies have provided analytical, experimental, and computational evidence of hot and cold spots formed around the convected vortical structures, at the fast and slow sides, respectively. Diffusive energy redistribution, due to the combined effects of the work by viscous stresses and of thermal conduction, is a second possible mechanism for energy separation. It is, in general, much weaker than the unsteady pressure mechanism discussed above, and best known in the context of thermal recovery in boundary layers.