3D end wall flow in a compressor cascade

Abstract

Improvement in calculation methods for end-wall boundary layers of blade rows can only come about through a greater understanding of the physics of the flow in that region. Most of the integral methods take the integration step as one chord, and differential methods use various turbulence models to predict the mean velocity profile because no realistic information is available within the passage. Detailed three-dimensional measurements of the boundary layer development on the blade passage end walls and within the tip clearance were made in a large-scale, low aspect-ratio compressor cascade.

Two sets of experiments were conducted: one for zero tip clearance to simulate the flow near the hub, and one for 4% tip clearance to simulate the flow in a conventional compressor tip region. This was supplemented by the measurement of the full Reynolds stress tensor and its distribution over the entire flow field. The structure of turbulence was studied to enhance understanding of the flow picture.

The results confirm that the wall shear stress obtained by the two-dimensional Ludwieg-Tillman relation, when applied to the streamwise profile, closely matches the value of the experimental stress when extrapolated to the wall. The logarithmic law of the wall, as for two-dimensional boundary layers, appears to be valid for the inner region of the experimental three-dimensional profiles. Mixing lengths and eddy viscosities have been derived from the experimental results.

The passage flow has been averaged using mass and momentum flux considerations to obtain representative velocities for use in design. The integral quantities and their development through the passage have been obtained and presented.