Three-dimensional boundary layer in a turbine blade passage

The boundary layer on the end wall of a turbine blade cascade is subject to cross-stream pressure gradients in the blade passage, which generate a cross-stream velocity component to make it three dimensional. This distorts the turbulence relative to a two-dimensional boundary layer and impacts the end wall heat transfer. This study presents measurements of the three-dimensional boundary layer in a turbine cascade obtained with a laser Doppler velocimeter. In addition, two types of Reynolds-Averaged Navier-Stokes models are compared to the measurements: The Shear Stress Transport k - ω model using the isotropic eddy viscosity assumption and a Reynolds stress model that allows for anisotropy of the Reynolds stress. Neither model fully captures the complexity of the three-dimensional boundary layer in a turbine blade passage, particularly for turbulence associated with the cross-stream flow and for the highly accelerated three-dimensional boundary layer at the passage exit. Measurements at the passage exit indicate a very thin boundary layer with laminarlike qualities. Because of the boundary-layer complexity, end wall heat transfer is not well predicted toward the pressure side and the exit of the blade passage.