An Automatic Wall Treatment for Spalart-Allmaras Turbulence Model

Assam, Ashwani and Kalkote, Nikhil Narayan and Sharma, Vatsalya and Eswaran, Vinayak (2018) An Automatic Wall Treatment for Spalart-Allmaras Turbulence Model. Journal of Fluids Engineering. ISSN 0098-2202 (Submitted)

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Abstract

The Spalart-Allmaras (SA) is one of the most popular turbulence models in the aerospace CFD community. In its original (low-Reynolds number) formulation it requires a very tight grid spacing near the wall to resolve the high flow gradients. However, the use of wall functions with an automatic feature of switching from the wall function to the low-Reynolds number approach is an effective solution to this problem. In this work, we extend Menter's automatic wall treatment (AWT), devised for the k$\omega$-SST, to the SA model in our in-house developed 3-D Unstructured grid density-based CFD solver. It is shown, for both momentum and energy equations, that the formulation gives excellent predictions with low sensitivity to the grid spacing near the wall, and allows the first grid point to be placed at $y^{+}$ as high as 150 without loss of accuracy, even for the curved walls. In practical terms, this means a near-wall grid 10-30 times as coarse as that required in the original model would be sufficient for the computations.

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