Two-equation heat-transfer model for turbulent flows with separation and reattachment

We propose a new two-equation heat-transfer model which is modified from the model developed by Nagano, Tagawa and Tsuji (Proc. ASME/JSME Thermal Eng. Joint Conf., 3 (1991), 233). The main improvement is made by introducing the Kolmogorov velocity scale, u_ε≡(νε) ^1/4 , instead of the friction velocity u_τ, to account for the wall-limiting behavior. After investigating the characteristics of various time scales for the heat-transfer model, we employed a composite time scale which gives weight to a shorter scale among the velocity- and temperature-field time scales. With these modifications, it is shown that the present model quite successfully predicts the turbulent heat transfer in a boundary layer subjected to sudden change of heat flux, and in a separating and reattaching flow downstream of a backward-facing step.