The Aerodynamic Mixing Effect of Discrete Cooling Jets With Mainstream Flow on a Highly Loaded Turbine Blade

Abstract

For the application of film cooling to turbine blades experimental investigations were performed on the mixing processes in the near hole region with a row of holes on the suction side of a turbine cascade. Data were obtained using pneumatic probes, pressure tappings, and a three-dimensional subminiature hot wire probe, as well as surface flow visualization techniques. It was found that at low blowing rates a cooling jet behaves very much like a normal obstacle and the mixing mainly takes place in the boundary layer. With increasing blowing rates the jet penetrates deeper into the mainstream. The variation of the turbulence level at the inlet of the turbine cascade and the Reynolds number showed a strong influence on the mixing behavior. The kidney-shaped vortex and as an important achievement the individual horse-shoe vortex of each single jet were detected and their exact positions were obtained. This way it was found that the position of the horse-shoe vortex is strongly dependent on the blowing rate and this influences the aerodynamic mixing mechanisms. A two-dimensional code for the calculation of boundary layer flows called GRAFTUS was used, however the comparison with the measurements showed only limited agreement for cascade flow with blowing due to the strong three-dimensional flow pattern.