Aerothermal Characterization of a Rotating Ribbed Channel at Engine Representative Conditions—Part II: Detailed Liquid Crystal Thermography Measurements

Abstract

The present twopart work deals with a detailed characterization of the flow field and heat transfer distribution in a model of a rotating ribbed channel performed in a novel setup which allows test conditions at high rotation numbers (Ro). The tested model is mounted on a rotating frame with all the required instrumentation, resulting in a high spatial resolution and accuracy. The channel has a cross section with an aspect ratio of 0.9 and a ribbed wall with eight ribs perpendicular to the main flow direction. The blockage of the ribs is 10% of the channel cross section, whereas the rib pitchtoheight ratio is 10. In this second part of the study, the heat transfer distribution over the wall region between the sixth and seventh ribs is obtained by means of liquid crystal thermography (LCT). Tests were first carried out at a Reynolds number of 15,000 and a maximum Ro of 1.00 to evaluate the evolution of the heat transfer with increasing rotation. On the trailing side (TS), the overall Nusselt number increases with rotation until a limit value of 50% higher than in the static case, which is achieved after a value of the rotation number of about 0.3. On the leading side (LS), the overall Nusselt number decreases with increasing rotation speed to reach a minimum which is approximately 50% of the one found in static conditions. The velocity measurements at Re = 15,000 and Ro = 0.77 provided in Part I of this paper are finally merged to provide a consistent explanation of the heat transfer distribution in this model. Moreover, heat transfer measurements were performed at Reynolds numbers of 30,000 and 55,000, showing approximately the same trend.