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12.8.1 Spalart-Allmaras RANS Model

The standard Spalart-Allmaras model uses the distance to the closest wall as the definition for the length scale $d$, which plays a major role in determining the level of production and destruction of turbulent viscosity (Equations  12.3-6, 12.3-12, and 12.3-15). The DES model, as proposed by Shur et al. [ 331] replaces $d$ everywhere with a new length scale $\tilde{d}$, defined as

 \tilde{d} = \min(d, C_{\rm des} \Delta) (12.8-1)

where the grid spacing, $\Delta$, is based on the largest grid space in the $x$, $y$, or $z$ directions forming the computational cell. The empirical constant $C_{\rm des}$ has a value of 0.65.


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