No abstract

A new transonic turbine cascade model that accurately produces infinite cascade flow conditions with minimal compressor requirements is presented. An inverse design procedure using the Favre-averaged Navier-Stokes equations and k‐ε turbulence model based on the method of steepest descent was applied to a geometry consisting of a single turbine blade in a passage. For a fixed blade geometry, the passage walls were designed such that the surface isentropic Mach number (SIMN) distribution on the blade in the passage matched the SIMN distribution on the blade in an infinite cascade, while maintaining attached flow along both passage walls. An experimental rig was built that produces realistic flow conditions, and also provides the extensive optical access needed to obtain detailed particle image velocimetry measurements around the blade. Excellent agreement was achieved between computational fluid dynamics (CFD) of the infinite cascade SIMN, CFD of the designed double passage SIMN, and the measured SIMN.

Turbulence measurements were made in a transonic turbine cascade using PIV in a unique two-passage model consisting of a single full blade and two shaped outer walls. The outer wall shapes were prescribed using an inverse design procedure that gave the correct infinite-cascade pressure and mean velocity distribution around the blade. The outer surfaces of the curved walls were shaped to steer a laser sheet to provide uniform illumination for the PIV. The PIV measurements were performed over a large number of small domains providing excellent spatial resolution over most of the flowfield. Measurements in the freestream above the blade boundary layers showed that the absolute magnitude of the turbulent stresses changed little through the strong acceleration and curvature. This means that the relative turbulence intensity falls rapidly as the flow accelerates through the cascade. Detailed comparison to various turbulence models is underway.

This paper presents two low-cost alternatives for turbine blade surface heat transfer and fluid dynamics measurements. These models embody careful compromises between typical academic and full-scale turbomachinery experiments and represent a comprehensive strategy to develop experiments that can directly test shortcomings in current turbomachinery simulation tools. A full contextual history of the wide range of approaches to simulate turbine flow conditions is presented, along with a discussion of their deficiencies. Both models are simplifications of a linear cascade: the current standard for simulating two-dimensional turbine blade geometries. A single passage model is presented as a curved duct consisting of two half-blade geometries, carefully designed inlet and exit walls and inlet suction. This facility was determined to be best suited for heat transfer measurements where minimal surface conduction losses are necessary to allow accurate numerical model replication. A double passage model is defined as a single blade with two precisely designed outer walls, which is most appropriate for flow measurements. The design procedures necessary to achieve a desired flow condition are discussed.