Impact of Flow Unsteadiness on Turbine Airfoil Heat Transfer via Streaming

Thermal management of turbine airfoils is a critical design consideration, but the impact of unsteadiness on heat transfer of attached flow regions has received less attention in the literature. When turbine surfaces are subjected to unsteady zero-mean flow fluctuations, either naturally or artificially, the mean velocity around them is modified due to a nonlinear interaction of fluctuations, known as streaming. In this numerical study, we examine the effect of streaming on heat transfer and skin friction in a simplified model of the flow over a turbine blade. Both heat transfer and skin friction modifications were found to strongly depend on the amplitude and wave speed of the unsteady flow perturbations. Over a wide range of disturbance parameters, skin friction modification was negligible, but a significant effect on heat transfer due to streaming was identified. Moreover, the impact of favorable pressure gradients, which are typical for turbine airfoils, on the streaming phenomena was also considered, and it was found that flow regions of zero-pressure gradient produced the strongest amplification of heat transfer, although the effect of the pressure gradient varied with Strouhal number. Due to its significant effect on wall heat transfer, the streaming phenomenon should be taken into account during the design and measurement of the thermal properties of unsteady systems.