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nuTilda (\(\tilde{\nu} \)) is a viscosity-equivalent variable required to be defined as a boundary condition while using the LES Spalart-Allmaras turbulence model. Spalart-Allmaras is an LES (Large Eddy Simulation) based model that solves for the transport of nuTilda. \(\tilde{\nu} \) is also referred to as Spalart-Allmaras variable.

nuTilda is not explicitly available in the list of boundary conditions and needs to be defined under Custom boundary condition in units of \(m^2/s\) or \((\).

Based on the chosen analysis type and simulation settings, the following options are available to define nuTilda:

  • Calculated
  • Symmetry
  • Fixed gradient
  • Fixed value
  • Inlet-outlet
  • Zero gradient
  • Wall function
  • Full resolution


In CFD simulations using LES models, turbulence variables at walls are defined as a fixed value of zero or zero gradient. This is only valid if the velocity at the wall is zero, i.e., no oscillations and therefore no turbulence.

Following is a snap from the workbench showing the Custom boundary condition utility:

images shows nutilda boundary condition definition in simscale
Figure 1: nuTilda being defined on one the faces using the Inlet-outlet method. An inlet value is required in this case.

Last updated: June 14th, 2021