Measurement of local heat transfer coefficient on the endwall of a turbine blade cascade by liquid crystal thermography

This paper presents convective heat transfer measurements on the endwall of a turbine blade cascade by means of the liquid crystal thermography. The measurement method is based on the heating, at uniform heat flux, of the endwall by means of an electronic circuit board. The heated region of the endwall surface exposed to the airflow is covered with a thermochromic liquid crystal coating. The colour map of the coating during a given test, featured by an assigned mass flow rate, is measured by using an image processing system. With a prescribed wall heat flux, the convective heat transfer coefficient is obtained, at every pixel location, from the measured temperature maps recorded at the steady-state. Heat transfer results, presented for the endwall of a high-pressure turbine cascade, have been obtained for different values of the Reynolds number. Regions of the endwall surface associated with high rates of heat transfer are well identified: the leading edge of blades, pressure and suction side corners, the blade wake and cascade throat. The spatially-resolved heat transfer measurements presented here could provide a useful baseline for a condition-specific, optimized endwall film-cooling solution that reduces overall heat transfer rates.