COMPUTATION AND SIMULATION OF WAKE GENERATED UNSTEADY PRESSURE AND BOUNDARY-LAYERS IN CASCADES .2. SIMULATION OF UNSTEADY BOUNDARY-LAYER FLOW PHYSICS

The unsteady pressure and boundary layers on a turbomachinery blade ro w arising front periodic wakes due to upstream blade rows are investig ated in this paper. Numerical simulations are carried out to understan d the effects of the wake velocity defect and the wake turbulence inte nsity on the development of unsteady blade boundary layers. The bounda ry layer transition on the blade is found to be strongly influenced by the unsteady wake passing. Periodic transitional patches are generate d by the high turbulence intensity in the passing wakes and transporte d downstream. The time-dependent transition results in large unsteadin ess in the instantaneous local skin friction coefficient and a smoothe r time-averaged transition curve, than the one observed in the steady boundary layer. A parametric study is then carried out to determine th e influence of wake parameters on the development of the unsteady blad e boundary layers. It is shown that the unsteadiness in the blade boun dary layer increases with a decrease in the axial gap, an increase in wake/blade count ratio, or an increase in the wake traverse speed. The time-averaged boundary layer momentum thickness at the trailing edge of the blade is found to increase significantly for higher wake/blade count ratio and larger wake traverse speed. Increase of the wake/blade count ratio also results in higher frictional drag of the blade.