Simulating Turbulence with Pitch-Wise Uniformity Across a Turbine Cascade Entrance

Abstract

Aircraft operating at high altitudes and low velocities are susceptible to turbine engine performance losses due to low operating Reynolds numbers in the turbine section. Cascade wind tunnels are used to simulate two-dimensional flow characteristics associated with turbine operating conditions in order to identify and suppress undesirable flow phenomena such as boundary layer separation. It is important to simulate pitch-wise uniform flow characteristics across the turbine cascade entrance. Two passive, square-bar turbulence generating grid arrangements were explored to simulate pitch-wise uniform turbulence, one grid assembly was perpendicular to the inlet flow and the other parallel to the turbine cascade. Reynolds numbers in this study were 50k and 100k, based on turbine axial chord, and grids were placed at three different locations upstream of the turbine cassette to simulate freestream turbulence intensities ranging from 3% to 6%. Turbulence produced by an innovative T-Bar turbulence grid assembly oriented parallel to the turbine cascade had better pitch-wise uniformity than that produced by a mesh grid oriented perpendicular to the inlet flow; however, blade-to-blade periodicity of surface pressure coefficient profiles appeared to be insensitive to turbulence grid configuration.

KURT ROUSER

United States Air Force Academy