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Variable Blade Tip Geometry Inserts for Combined Aerothermal Measurements for Bladed Disk Rotors

Cost effective experimental testing in turbomachinery requires the integration of multiple geometries in one rotor. So-called rainbow designs, combined with fast response aerodynamic and entropy probes, allow for experimentally investigating different designs in a timely and cost effective manner. The investigation of new blade tip geometries is of particular interest, because tip leakage losses account for approximately one third of the total aerodynamic losses in a turbine stage. This work presents the design, integration, and testing of a variable and exchangeable blade tip setup integrated in a bladed disk rotor. The key features of the concept are high flexibility of the geometry, coupled with the possibility of introducing blade tip coolant flows in bladed disk arrangements, and the integration of tip heat transfer measurements. After successful bench tests, an existing rotor has been modified with three tip inserts of the same geometry, and subsequently tested in the axial turbine research facility LISA at ETH Zurich. A custom-made thin film heater for optical highresolution heat transfer measurements was successfully integrated on the insert and tested during operation. Flow field measurements behind the rotor indicated that the aerodynamics of the rotor is not influenced by installing tip inserts. The setup has proven its robustness in more than 80 days of experimental testing, and has provided some encouraging tip heat transfer data.