Extending the Capabilities of a High-Speed Wind Tunnel to Secondary Flow Measurements in Transonic Linear Turbine Cascades

Abstract

Since its commissioning, the Carleton University High-Speed Wind Tunnel has been used extensively for midspan aerodynamic measurements in transonic axial turbine cascades. Recently, a requirement has arisen to obtain three-dimensional, endwall flow data in turbine cascades in this facility. Three dimensional loss measurements in high-speed turbomachinery cascades and rotating rigs have often been obtained using Kiel probes. These probes have the advantage of giving direct measurements of the total pressures, thus allowing losses to be obtained with minimal data reduction and without resort to complex probe calibrations. On the other hand, they cannot be used to obtain flow direction and local estimates of static pressure. As a result they do not permit other important information to be obtained, such as secondary kinetic energy, axial velocity and vorticity distributions. This limits the ability to gain physical insights into the flow behaviour. An alternative to Kiel probes is the multi-hole pressure probe. The present study was intended to develop the ability to obtain detailed three-dimensional flow field measurements in our facility using primarily a seven-hole pressure probe. The measurements are compared with the equivalent total pressure measurements obtained with a Kiel probe of similar spatial resolution. The uncertainty in losses introduced by the processing of multiple pressure-port measurements, and the use of complex probe calibration data, is weighed against the advantages of the more detailed flow field data that are obtained. The results from two linear turbine cascades with different Zweifel coefficients are presented here. The results contribute a small addition to the data available on the effects of compressibility on secondary flows. Planned measurements will make substantial contributions in that direction in the future.