THE AERODYNAMIC MIXING EFFECT OF DISCRETE COOLING JETS WITH MAINSTREAM FLOW ON A HIGHLY LOADED TURBINE BLADE

For the application of film cooling to turbine blades, experimental in vestigations were performed on the mixing processes in the near-hole r egion with a row of holes on the suction side of a turbine cascade. Da ta were obtained using pneumatic probes, pressure tappings, and a thre e-dimensional subminiature hot-wire probe, as well as surface flow vis ualization techniques. It was found that at low blowing rates, a cooli ng jet behaves very much like a normal obstacle and the mixing mainly takes place in the boundary laver. With increasing blowing rates, the jet penetrates deeper into the mainstream. The variation of the turbul ence level at the inlet of the turbine cascade and the Reynolds number showed a strong influence on the mixing behavior. The kidney-shaped v ortex and as an important achievement the individual horseshoe vortex of each single jet were detected and their exact positions were obtain ed. This way it was found that the position of the horseshoe vortex is strongly dependent on the blowing rate and this influences the aerody namic 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.