Experimental Investigations of the Influence of Incoming Wakes on the Losses of a Linear Turbine Cascade

Abstract

The objective of this work is to enhance the understanding of the influence of wake induced non-uniform, steady inlet flow conditions on the profile losses of highly-loaded turbines. For different Reynolds numbers wake and profile pressure distribution measurements were carried out on a linear subsonic turbine cascade as well as measurements with a single sensor hot-film probe. The non-uniform inlet flow were simulated with two different cascades of cylindrical bars. The measurements with various circumferential positions of the incoming wakes relative to the turbine cascade show at low Reynolds numbers a decrease of the losses compared to uniform inlet conditions, because no separation of the suction side boundary layer occurs. With increasing Reynolds numbers the non-uniform inlet flow conditions cause an increase in the losses compared to uniform inlet conditions, due to the forward shift of transition. Generally, the smallest influence of the non-uniform incoming flow can be observed when the wakes enter the cascade inlet plane between the pressure-side of the profiles and the middle of the blade passage. Incoming wakes have the highest influence when they enter the blade passage near to the suction side of the profiles.