Heat Transfer in the Tip Region of Grooved Turbine Blades

Abstract

Local convective heat transfer at the tip region of grooved blades is experimentally investigated. The present study models the problem by flow over a shrouded, rectangular cavity, with the shroud moving opposite to the main flow direction. The naphthalene sublimation technique together with a computer-controlled measurement system provides detailed local transfer information on all the participating surfaces. The local heat transfer coefficient in the cavity is strongly influenced by the cavity aspect ratio, gap size, and leakage flow Reynolds number. Within the present study range, the effect of relative motion between the shroud and cavity on the heat transfer is found to be minor, particularly for the average heat transfer coefficient. With the same leakage flow rate, the average heat transfer coefficient over the entire tip area decreases with an increase in cavity depth. However, in terms of total heat transfer to the tip, an overly deep cavity is undesirable, because it provides larger surface area but only a small increase in flow resistance.