Visualization and analysis of supersonic flow in rotating turbine stage (3rd report, influence of a supersonic turbine stage on flows of subsequent stationary blades)

Transonic flows in turbine stages are complex and unsteady. Unsteady phenomena in shockwave reflection, vortices and boundary layer separation affect the reliability and efficiency of turbines, and the influence of flow through the stage on subsequent stationary blades is large. Not only the analysis of the calculated results but also experimental studies are needed to clarify such unsteady phenomena in the turbine stage. In this study, a small-size turbine was improved by installing stationary blades at the stage subsequent to that which is supersonic. It was investigated whether there are influences of the flow fluctuation caused by rotation of blades on the flow in the channel of subsequent stationary blades behind the rotating cascade, and if there exists generation of vortices at the trailing edge. The waves due to pressure fluctuation corresponding to the period of blade rotation blade were observed on both sides of the trailing edge. Furthermore, it was found that this amplitude of fluctuation on the pressure side was about twice as large as that on the suction side. The mixing of the flows of pressure and suction side makes vortices behind the trailing edge large with Strouhal Number 0.2approx.0.3.