Performing Heat Transfer Experiments in Blade Cooling Circuits Using a Transient Technique With Thermochromic Liquid Crystals

Abstract

Blades and vanes in the first stages of modern gas turbines are exposed to high thermal loads. As the resulting temperatures exceed the temperature stability of the material, it is necessary to validate the internal cooling capability of these parts experimentally, before proving their reliability in service. In the present state of the art a commonly used experimental method for evaluating heat transfer coefficients is given by the transient technique using thermochromic liquid crystals (TLCs). Though it is easily applicable for short single-pass and simple-shaped cooling channels, additional aspects must be considered for small engine-representative 3D cooling circuits that have a complex multi-pass system. Mass flow splits and space-time-dependent fluid temperatures may be noted as examples. To point out and suggest solutions for these characteristics, we therefore present a procedure for conducting transient heat transfer experiments using TLCs with respect to engine-representative, complex 3D cooling circuits in particular. General design and dimensioning guidelines are given by means of exemplary geometries. Furthermore, an approach for the experimental setup, preparation of models, and test procedure is discussed. The experiments were conducted with an engine-representative Reynolds number and Mach number and the same heat flux direction as in a real blade. We evaluated the present method and performed an uncertainty analysis where the technique demonstrated robustness for a variety of investigated geometries.