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Spalart-Allmaras Delayed Detached Eddy Simulation (DDES)

Properties​

  • One equation model based on a modified turbulence viscosity, ν~\tilde{\nu}
  • based on the Spalart-Allmaras DES model.

Model equations​

The model equations are the same as used by the DES variant of the model, with a different approximation for d~\tilde{d}:

d~=max⁡[LRAS−fd,max⁡(LRAS−LLES,0)] \tilde{d} = \max \left[ L_{RAS} - f_d, \max (L_{RAS} - L_{LES}, 0) \right]

The RAS length scale is:

LRAS=y L_{RAS} = y

and the LES length:

LLES=ΨCDESΔ L_{LES} = \Psi C_{DES} \Delta

The delay function is given by:

fd=1−tanh⁡[(Cd1rd)Cd2] f_d = 1 - \tanh \left[ \left( C_{d1} r_d \right)^{C_{d2}} \right]

Here, when fd=0f_d = 0 RAS is recovered, and when fd=1f_d = 1 the DES mode is recovered. The rdr_d parameter is given by:

rd=min⁡(νeff∣∇u∣κ2y2,10) r_d = \min \left( \frac{\nu_{\mathit{eff}}}{\mag {\grad \u} \kappa^2 y^2}, 10\right)

Default model coefficients​

Initialisation​

Usage​

The model is specified using:

LES
{
    turbulence      on;
    LESModel        SpalartAllmarasDDES;
}

Boundary conditions​

Inlet

Outlet

Walls

  • wall functions

Further information​

Source code:

References:

  • Spalart et al. 68