Wake-Induced Boundary Layer Transition in a Low-Speed Axial Compressor

The boundary layer on the blades of turbomachines substantially influences the loss production of the machine as well as the heat transfer between the blade surface and the fluid. For this reason the knowledge of the boundary layer structure and development plays an important role for the understanding and further improvement of turbomachines. The incoming wakes of the upstream blade rows strongly periodically influences the boundary layer on turbomachine blades. For this reason an unsteady, highly complex boundary layer behaviour can be observed. This paper presents experimental results of the unsteady boundary layer behaviour on the first stage stator blades of the four-stage Dresden Low-Speed Research Compressor. Different operating points of the compressor are investigated. Special consideration is taken on the analysis of the time-resolved structure of the incoming flow field and the unsteady boundary layer response. The wake passing triggers a periodic transition of the boundary layer starting already at the leading edge of the blade. The wake-induced transitional regions limit the extension of the laminar boundary layer in the front part of the blade. An improved description of the complex boundary layer structure is given.