A mixed very-large eddy simulation model for turbulent convective heat transfer and applications for cylindrical pin matrix and cutback film cooling

The study presents a new improved Very-Large Eddy Simulation (VLES) model via combining two different modeling modes for better prediction accuracy of turbulent convective heat transfer. The proposed VLES approach utilizes individual method to model the near-wall turbulence and free-shear flow turbulence, respectively, and combines them together to form a new mixed VLES model. For comparisons, traditional Large Eddy Simulation (LES) method with the dynamic Smagorinsky–Lilly subgrid-scale (sgs) model, LES with the Wall-Adapting Local Eddy-viscosity sgs model, as well as the Reynolds-Averaged Navier–Stokes (RANS) method are also applied for the test cases. Typical cases of convective heat transfer around bluff body as well as trailing edge cutback film cooling are selected for applications to validate the prediction accuracy of the proposed mixed method. For the bluff body cases, flow and heat transfer around a single square cylinder and a cylindrical pin matrix with wall-oriented 8 × 8 pins are numerically studied and analyzed. The VLES predictions demonstrate good agreement with experimental results for both the flow field as well as the mean Nusselt number in the single square cylinder case, outperforming both the traditional LES and RANS methods. For the pin-matrix case, all three methods yield satisfactory results for velocity. However, for the heat transfer, the VLES method shows significant advantages than LES and RANS, and the discrepancy between the numerical prediction and the experiment for the mean end wall Nusselt number of the pinned matrix is around 2.3% from VLES compared with that of 16.7% from LES. On the basis, the proposed VLES method is applied to study the film cooling of a simplified trailing edge cutback in a turbine blade. The adiabatic film cooling effectiveness of the cutback surface shows that both the VLES and LES methods perform well and reproduce the experimental results satisfactory, which demonstrate significant advantages than RANS method. Overall, the proposed mixed VLES method can handle a variety of unsteady flow and convection heat transfer mechanisms well and thus has the capacity for a wide range of applications.