The Transport of Vortices Through a Turbine Cascade

Abstract

An experiment was conducted to determine how incident vortices created by upstream blade rows interacted with a downstream turbine cascade. Specifically, the kinematics of the vortex transport through turbine blade passages was investigated. A stationary water table and a flow visualization system using the pH indicator Bromothymol Blue was used to visualize the vortices generated by vortex generators placed upstream of a turbine blade cascade. Two test series were conducted. In the first test series, stationary vortex generators were positioned at various locations along the turbine blade pitch to observe how a steady incident streamwise vortex was transported through the turbine cascade. Observations showed an unsteady vortex response of the streamwise vortex when the incident vortex was located at the stagnation area of the blade. In the second test series, the vortex generators were moved to simulate the relative motion of an upstream blade row. In these tests, the unsteady vortex response was no longer seen at the stagnation region but was instead located at the suction side of the blade. In addition, the breakdown of the vortex varied greatly with the reduced frequency of the incident vorticity and showed an “explosive” type vortex breakdown that occurred at reduced frequencies greater than 8. The dissimilar behavior between the stationary and moving incident vortices indicates that losses and leading edge heat transfer could differ to some degree when determined from a stationary test as opposed to a full-stage simulation.