Required field
Required field
Required field
Required field

Documentation

# nuTilda

nuTilda ($$\tilde{\nu}$$) is a viscosity-equivalent variable required to be defined as a boundary condition while using the Spalart-Allmaras turbulence model. Spalart-Allmaras is a RANS (Reynolds Averaged Navier Stokes) based one-equation 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 $$(lbf.s.in)/lb$$. It is only available for CFD simulations.

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

• Calculated: The value is calculated based on other turbulence quantities.
• Symmetry: Used when the geometry is symmetric
• Fixed gradient: The spatial variation is constant.
• Fixed value: The value is constant.
• Inlet-outlet: Inlet value needs to be specified. Outlet value is at zero gradient.
• Zero gradient: The value doesn’t vary spatially.
• Wall function: Using a function to calculate variables at walls.
• Full resolution: Walls are fully resolved using a fine mesh with inflation layers.

Note

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:

Last updated: August 24th, 2022