Session Ce - Separated Flows.
ORAL session, Sunday, November 23
305, Moscone Center
A transitional two-dimensional separation bubble was created on a flat plate in the MTL wind tunnel using an adjustable hump at the upper wall to establish the pressure gradient. Linear and nonlinear development of natural and artificially introduced wave packets in the boundary layer was studied using hot wire anemometry. In the vicinity of the source TS-waves typical for the Blasius boundary layer were observed. A third maximum in between the two maxima of the TS-wave amplitude profile was found to be associated with an inflectional streamwise mean velocity profile in the adverse pressure gradient and separation regions. Both velocity correlation measurements and smoke visualization revealed that the unsteady vortical structure was still two-dimensional just prior to the reattachment of the shear layer, whereas both steady and unsteady flow structures in the reattachment region was found to be essentially three-dimensional. In the numerical simulation good agreement in mean flow parameters was found when the measured normal velocity was used as free stream boundary conditions. In those calculations the growth characteristics of small amplitude two-dimensional disturbances also agreed well with the measured values.