Experimental study of thermal development in a rotating square-ended U-bend

This paper reports an experimental study of the thermal development in an idealized model of a blade cooling passage of smooth inner surfaces, comprising a square-ended U-bend with a cross-section that changes from a square upstream to a 2:1 rectangle downstream of the turn. The two flat walls are heated electrically, while the outer wall and the splitter plate are thermally insulated. The steady state liquid crystal technique is used to map the local Nusselt number variation. Measurements are obtained using a stationary air flow facility and also a rotating water flow facility. This enables us to investigate the effects on the thermal development of the variation in Reynolds from 30,000 to 100,000, in Prandtl number from 0.7 to 5.8 (both for static conditions) and in rotation number, from 0 to 0.4. The effects of minor modifications in the cross-sectional area at the bend exit, on the thermal development, under both stationary and rotating conditions, are also explored.