Unsteady 3D Reynolds-averaged Navier–Stokes (RANS) simulations have been performed on a highly loaded transonic turbine stage, and results are compared with steady calculations and experiments. A low Reynolds number $k-ε$ turbulence model is employed to provide closure for the RANS system. A phase lag boundary condition is used in the tangential direction. This allows the unsteady simulation to be performed by using only one blade from each of the two rows. The objective of this paper is to study the effect of unsteadiness on rotor heat transfer and to glean any insight into unsteady flow physics. The role of the stator wake passing on the pressure distribution at the leading edge is also studied. The simulated heat transfer and pressure results agree favorably with the experiment. The time-averaged heat transfer predicted by the unsteady simulation is higher than the heat transfer predicted by the steady simulation everywhere, except at the leading edge. The shock structure formed, due to stator-rotor interaction, is analyzed. Heat transfer and pressure at the hub and casing are also studied. Thermal segregation is observed that leads to the heat transfer patterns predicted by steady and unsteady simulations to be different.

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