Wall Shear Stress Measurements on a Highly Loaded Compressor Cascade

Abstract

This paper presents wall shear stress measurements obtained with a new type of wall-mounted probe based on the thermal electrical principle. The sensor consists of three single surface hot wires arranged in a δ configuration. This allows for measuring wall shear stress magnitude and direction simultaneously. Each probe has to be calibrated in a flat plate experiment for a number of wall shear values and flow directions before applying it to the relevant flow situation. To assess the full potential of the newly designed sensors, they were applied to a low-speed, large-scale cascade test section equipped with highly loaded compressor blades. The high blade loading in conjunction with a small blade aspect ratio results in a strongly three-dimensional flow field with large secondary flow structures and flow separation. Furthermore, laminar separation bubbles can be observed on the blade surface. The wall shear stress distribution allows for resolving these existing flow structures and provides detailed insight into the flow on the blade’s surface. The additionally measured flow direction reveals further details of the flow field. Parallel to the experiments, RANS simulations were conducted using the commercial flow solver CFX to compare the simulated results with the measured values.