Comparison of Steady and Unsteady RANS Heat Transfer Simulations of Hub and Endwall of a Turbine Blade Passage

The necessity of performing an unsteady simulation for the purpose of predicting the heat transfer on the endwall surfaces of a turbine passage is addressed. This is measured by the difference between the two solutions obtained from a steady simulation and the time average of an unsteady simulation. The heat transfer coefficient (Nusselt number) based on the adiabatic wall temperature is used as the basis of the comparison. As there is no film cooling in the proposed case, a computed heat transfer coefficient should be a better measure of such difference than, say, a wall heat flux. Results show that the effect of unsteadiness due to wake passage on the pressures and recovery temperatures on both hub and casing is negligible. Heat transfer on the endwalls, however, is affected by the unsteady wake; the time-averaged results yield higher heat transfer; in some regions, up to 15% higher. The results for the endwall heat transfer were compared with results in open literature and were found to be comparable.