INVESTIGATION OF TRAILING EDGE COOLING CONCEPTS IN A HIGH PRESSURE TURBINE CASCADE – ANALYSIS OF THE ADIABATIC FILM COOLING EFFECTIVENESS

Kurzfassung

Within a European research project experimental studies were performed concerning the determination of the film cooling efficiency on the pressure side of trailing edges of high pressure turbine blades. The experiments were carried out at the linear cascade wind tunnel (EGG) of the German Aerospace Center (DLR), Göttingen. The thermodynamic investigations were performed using the same cascade geometries and trailing edge configurations as for the aerodynamic measurements. Two different trailing edge geometries with coolant ejection were investigated. The first configuration was equipped with a pressure side cutback while for the second configuration the pressure side film cooling was realized by a row of cylindrical holes. The determination of the surface temperatures was done by using a combination of IR-thermography and thermocouples. Preliminary studies showed the feasibility to use metallic surfaces of the suction side of the adjacent blade as a mirror for IR-thermography. Thus it is possible to observe the pressure side near the trailing edge of interest by means of an infrared camera. The camera was mounted outside of the cascade’s free stream ensuring no influence to the aerodynamic boundary conditions. Up to seven flush mounted thermocouples on each side of the trailing edge were used for an in-situ calibration of the infrared pictures and thermal loss calculations. The distributions and averaged values of the film cooling efficiency are in agreement with aerodynamic measurements [9]. The results for the cutback configuration with 0.5% mass flow rate ejected show an accumulation of coolant just behind the coolant slot which is caused by a vortex in the dead region of the cutback. In case of 1.0% mass flow rate a refilling of this region with coolant is indicated. For higher mass flow rates the distributions of the film cooling efficiency looses it’s homogeneity due to flow separations on some ribs of the pin fin array inside of the slot. For the configuration with pressure side bleeding the best coverage could be obtained applying 1.0% mass flow rate.