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THE INFLUENCE OF DISTURBANCES CARRIED BY PERIODICALLY INCOMING WAKES ON BOUNDARY LAYER SEPARATION ALONG THE SUCTION SIDE OF A TURBINE BLADE

Jan Wissink
Brunel University

Wolfgang Rodi
Institute for Hydromechanics,University of Karlsruhe, D-76128 Karlsruhe, Germany

Howard P. Hodson
Whittle Laboratory, University of Cambridge Madingley Road, Cambridge CB3 OD, UK

Abstract

The effect of fluctuations, caused by periodically incoming wakes, on a separated boundary layer are studied using direct numerical simulations of incompressible flow in the T106A low-pressure turbine cascade. To be able to differentiate between the effect of small scale fluctuations and large-scale fluctuations, in one of the simulations small scale disturbances have been removed from the wake before it enters the computational domain. It is shown that the large scale disturbance, associated with the presence of the mean wake, triggers the Kelvin-Hemholtz instability of the separated shear layer along the downstream half of the suction side, which is also observed in experiment. The small-scale disturbances are found to both seed the transition to turbulence of the rolled up shear layer flow and the production of kinetic energy observed at the apex of the wake inside the passage between blades (Wu and Durbin, JFM 446, 2001).