Effects of prandtl numbers on heat transfer of backward-facing step laminar flow with a pulsating inlet

The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.