Investigation of the unsteady rotor boundary layer transition in a transonic high pressure turbine stage

Abstract

The experimental determination of the laminar-to-turbulent transition processes in the boundary layers of a transonic high pressure turbine rotor blade is described. The results are based on qualitative wall shear stress data, being derived from surface hotfilm anemometer measurements. Two different transition modes formed a periodic-unsteady, multimoded transition process on the rotor suction side. Neither the variation of the stator trailing edge coolant ejection nor the variation of the inter-blade row gap led to noticeable changes. The data indicates that the periodically disturbed suction side boundary layer is less susceptible to bubble bursting than the undisturbed flowfield. Thus, unsteady effects in high pressure turbines may allow for a reduction of the number of rotor blades. The pressure side boundary layer was not significantly affected by passing wakes or shocks. The comparison of the determined transition patterns to predictions which were obtained from empirical correlations revealed that these models lack the required accuracy