The Influence of Boundary Layer State on Vortex Shedding From Flat Plates and Turbine Cascades

The paper aims at a better understanding of the reasons for the wide range of Strouhal numbers observed on turbine blades. The investigation is restricted to the subsonic domain. First, flat plate model tests are carried out to investigate the effect of both the boundary layer state and trailing edge geometry on the vortex shedding frequency. A particular objective of the tests is to obtain data for the very common case of a mixed laminar-turbulent separation from turbine blades. These basic tests are followed by three cascade tests with blades of very different suction side velocity distributions. Based on the experience gained from the flat plate test program, an attempt is made to interpret the Strouhal number variation with Mach number and Reynolds number, and to relate the vortex frequency change to the boundary layer state on the blade surfaces.