Unsteady shock wave effects on transonic turbine cascade performance

Abstract

The capability for experimental assessment of unsteady shock wave effects on turbine blade performance has been developed. A novel shock-generation system utilizing a shotgun blast has been implemented into the Virginia Tech Wind Tunnel Transonic Cascade Facility. Specialized optical systems and high-performance pressure instrumentation were utilized to obtain both qualitative and quantitative information.

Shadowgraph photos of the unsteady shock wave propagation through the cascade indicate presence of a vortical region and its movement from the blade surface into the passage flow. A previously unseen distortion of the trailing edge shock wave is also identified. High-frequency blade surface pressure measurements reveal large fluctuations in surface pressure during shock passage. An estimate of unsteady blade lift is made which reveals a 120 percent peak-peak variation. Furthermore, an approximated loss coefficient was determined to fluctuate as much as 40 percent near the blade passage center. Comparisons are made with previously-published experimental and analytical results.