Measurements of Secondary Losses in a Turbine Cascade With the Implementation of Non-Axisymmetric Endwall Contouring

An approach to endwall contouring has been developed with the goal of reducing secondary losses in highly loaded axial turbo-machinery. The present paper describes an experimental assessment of the performance of the contouring approach implemented in a low speed linear cascade test facility. The study examines the secondary flows of a cascade composed of Pratt and Whitney PAKB airfoils. This airfoil has been used extensively in low pressure turbine research and the present work adds intra-passage pressure and velocity measurements to the existing database. The cascade was tested at design incidence and at an inlet Reynolds number of 126,000 based on inlet midspan velocity and axial chord. Quantitative results include seven hole pneumatic probe pressure measurements downstream of the cascade to assess blade row losses, and detailed seven hole probe measurements within the blade passage to track the progression of flow structures. Qualitative results take the form of oil surface flow visualization on the endwall and blade suction surface. The application of endwall contouring resulted in lower secondary losses and caused a reduction in secondary kinetic energy associated with pitchwise flow near the endwall and spanwise flow up the suction surface within the blade passage. The mechanism of loss reduction is discussed in regards to the reduction of secondary kinetic energy.