Influence of a Periodical Fluctuation on a Profile Loss of a Cascade : Part II, Behavior of a Boundary Layer

Abstract

Unsteady boundary layers on a cascade in a periodically fluctuating flow have been investigated using an ensemble averaging technique. Time averaged velocity profiles, ensemble averaged instantaneous velocity distributions and turbulence in boundary layers on a test cascade have been obtained. A mechanism of the change in loss characteristics due to a fluctuation has been discussed from the behavior of boundary layers. Boundary layer thickness, 99% thickness, of a lightly loaded cascade remarkably increases with a rise in the intensity of a fluctuation, but momentum thickness is not so affected because some compensating effects occur in a change in velocity profiles. The growth in turbulence in a boundary layer is suppressed by a periodical fluctuation. In the case of a highly loaded cascade, a dynamic stall occurs during a cycle of fluctuation, but the stall is rapidly reestablished as the intensity increases, which causes an enlargement of the unstalled range of operation. However, these effects saturate at the intensity of 810%.