Analytical wall-function strategy for the modelling of turbulent heat transfer in the automotive CFD applications 2019-01-0206
Due to prohibitive computational costs, industrial CFD engineers still utilize classical wall-function approach as an affordable and practical strategy for the Reynolds-averaged Navier-Stokes (RANS) simulations of complex three-dimensional heat and fluid flows. Unlike the standard log-law wall-functions, the performance of the analytical wall function (AWF) significantly improves predictions of mean velocity and temperature fields in a wide range of attached and separated turbulent flows. In the AWF, simplified mean flow and energy equations are solved analytically over the control volumes in the near-wall cells, assuming a proper variation of the turbulent viscosity and accounting for the pressure gradient effects. Furthermore, the AWF has been extended for high Prandtl number turbulent flows with and without wall roughness, yielding better predictions in the flows featuring separation and impingement, with a very low grid sensitivity. Nevertheless, this advanced approach has not been extensively used in the industrial CFD applications. This is mainly due to the fact that its predictive accuracy depends on the turbulence model employed in the main flow field. As the model was originally intended for coarser mesh configurations, potential stability issues may arise due to pressure gradient sensitivity if employing locally inappropriate mesh layers, typically associated with the complex geometry details. This work presents the AWF-based formulation for the energy equation, whereas the main flow field is computed employing the k-ζ-f turbulence model and the hybrid wall treatment.The underlying turbulence modeling approach has been widely validated in numerous industrial applications, demonstrating capability (in terms of both accuracy and robustness) to capture near-wall transport phenomena with more fidelity compared to the standard or low-Re variants of the k-ε turbulence model. The proposed AWF strategy is validated on several benchmarks involving the representative pipe flows with strong temperature gradients and fluid property variations, and flows in more complex configurations such as IC engine and E-motor cooling jacket. The results confirm very low mesh sensitivity and superiority of the proposed model to the conventional RANS wall heat transfer models.
Sanjin Saric, Branislav Basara, Kazuhiko Suga, Simon Gomboc
AVL LIST GmbH, Osaka Prefecture University, ME Dpt., AVL-AST d.o.o