Effect of the Tip Clearance on End Wall Heat-Transfer in a HP Turbine

The present investigation analyzes the effect of the extension of the radial gap on the heat transfer at the blade tip and the casing within a high-pressure turbine stage of an aircraft engine. Due to the rotation and the interaction of the adjacent blade-rows, the flow field in the tip region of an unshrouded rotor-blade is characterized by a high level of unsteadiness. Furthermore, the casing is exposed to the passing blade-gap and corresponding changes in the velocity-profile, the resulting near-wall velocity-gradients, and the resulting changes in heat transfer. In order to account for these effects, time-resolved RANS computations of three different radial gaps are performed and evaluated. The present analysis shows an influence of the radial gap on the characteristics of the steady and unsteady heat transfer and a correlation with the size of the tip-clearance vortex can be shown.