Experimental Analysis of the Unsteady Turbulent Boundary Layer Flow with Separation on Turbine Blades

Abstract

The influence of periodically unsteady perturbations on the turbulent flow along the suction side of turbine blades is investigated in a test rig. The blade suction side is represented by a flat plate. The pressure profile typically encountered in a turbine blade channel is generated by a curved wall opposite to the flat plate. The angle of the divergent part of the test section and hence the pressure can be increased to induce flow separation on the flat plate. For the simulation of wakes being shed from upstream blade rows the incoming flow is periodically disturbed by a wake generator. A 2D-LDV with high spatial resolution is used to measure averaged and fluctuating components of the velocity inside the boundary layer flow. By Fourier analysis of the measured time related velocity distributions the stochastic and periodic parts of the overall turbulence are identified.

The structure of the boundary layer flow is investigated for both steady and unsteady flow conditions. With the periodic wake flow the separation is shifted downstream as compared to the steady flow situation. Conclusions derived from the experimental results for the theoretical understanding are discussed in particular with respect to turbulence modelling.