Separation control by acoustic excitation on highly loaded low pressure turbine blades

Authors

Bernardini, C., Benton, S.I., Bons, J.P. - Ohio State University, Columbus, Ohio, USA

Abstract

Flow control is a valuable route to overcome laminar separation in highly loaded lowpressure turbine blades at low Reynolds number. The present work aims to explore the possibility of flow control by external acoustic excitation, which provides further insight into the mechanisms that can be exploited for control. Two blade profiles with aft- and frontloaded velocity distributions have been tested in a low-speed wind tunnel. A loudspeaker is mounted atop the tunnel, upstream of the inlet section. Wake loss surveys show that the most effective frequencies of the excitation are found to be in the range of the fundamental frequency of the separated shear layer. Particle image velocimetry data show that perturbations at this frequency enhance coherence of vortices shed from the separating shear layer, which increases momentum exchange thus favoring separation reduction. Although best effectiveness is accomplished with low turbulence level, sound control is still effective even with an engine representative level, particularly for the aft-loaded profile