Spalart-Allmaras Detached Eddy Model Reference

The Spalart-Allmaras Detached Eddy model combines features of the Standard Spalart-Allmaras RANS model in the boundary layers with a large eddy simulation (LES) in unsteady separated regions.

The DES version of the Spalart-Allmaras model contains modifications to the damping functions recommended by Squires and others [364]. These modifications do not affect the predictions of fully turbulent flows, but prevent spurious upstream propagation of the eddy viscosity into attached laminar regions.

For the Spalart-Allmaras model, the DDES approach is implemented in Simcenter STAR-CCM+. In addition, the IDDES formulation is available as an option.


Theory	See Theory Guide—Spalart-Allmaras DES.
Provided by	[physics continuum] > Models > Detached Eddy Simulation
Example Node Path	Continua > Physics 1 > Models > Spalart-Allmaras Detached Eddy
Requires	(Deactivate the Auto-select recommended physics models checkbox.) Space: Three Dimensional Time: Implicit Unsteady or PISO Unsteady Material: one of Gas, Liquid, Multiphase, Multi-Component Gas, Multi-Component Liquid Viscous Regime: Turbulent Turbulence: Detached Eddy Simulation
Properties	See Properties.
Activates	Physics Models	Wall Distance: Wall Distance*
		Wall Treatment: All y+ Wall Treatment and Low y+ Wall Treatment
		Optional Models: Anisotropic Linear Forcing
	Model Controls (child nodes)	Curvature Correction Parameters (optional, see Curvature Correction Option) IDDES Coefficients (optional, see Formulation Option)
	Methods	Convection See Methods.
	Reference Values	Maximum Number of Eddies See Reference Values.
	Initial Conditions	Turbulence Specification Synthetic Turbulence Specification See Initial Conditions.
	Boundary Inputs	See Boundary Settings.
	Region Inputs	See Region Settings.
	Solvers	Spalart-Allmaras Turbulence Spalart-Allmaras Turbulent Viscosity See Spalart-Allmaras Solvers Reference .
	Monitors	Sa_nut (modified diffusivity)
	Field Functions	See Field Functions.

Properties

The Spalart-Allmaras Detached Eddy model owns the same properties as the Standard Spalart-Allmaras model, see Spalart-Allmaras Model Reference - Properties Lookup. The following properties are specific to the DES version of the model:

Cdes

The DES length scale coefficient

C_{D E S}

in Eqn. (1408) and Eqn. (1412).

CdesTimeLim

The DES blended upwind scheme time scale coefficient

C_{desT}

in Eqn. (1452).

Formulation Option

Selects the DES formulation to use.

DDES: Selects the DDES formulation.
IDDES: Selects the IDDES formulation. This formulation requires the coefficients $C_{t}$ in Eqn. (1418), $C_{l}$ in Eqn. (1419), and $C_{d t}$ in Eqn. (1423).

IDDES Coefficients

Child node that provides the parameters Ct, Cl, and Cdt.

Low Re Correction

Controls whether to apply a low Reynolds number correction.

When On, the low Reynolds number correction factor

ψ

in Eqn. (1408) and Eqn. (1412) is computed as in Eqn. (1411). When Off,

ψ

is set to 1.

Methods

Convection

For the Segregated Flow Model, the following additional convection methods become available:

Method	Corresponding Method Node
Hybrid This scheme blends second-order upwind and central differencing.	None.
Bounded-Central This scheme applies a boundedness criterion that makes the scheme more robust than central-differencing alone. Use this scheme for complex turbulent flows.	Bounded Differencing Provides the Upwind Blending Factor, which specifies the proportion of upwind differencing, $ς_{u b f}$ related to Eqn. (891). The default value provides the most robustness for the scheme. Reducing it would, in principle, increase accuracy. However, unless you are thoroughly familiar with the theoretical aspects of bounded differencing, do not change this property. The default value reflects optimization for accuracy and performance.
Hybrid-BCD This scheme blends second-order upwind and bounded-central differencing. This scheme is the default scheme for detached eddy simulation (DES).	As for Bounded-Central.

Method

Corresponding Method Node

Hybrid

This scheme blends second-order upwind and central differencing.

None.

Bounded-Central

This scheme applies a boundedness criterion that makes the scheme more robust than central-differencing alone.

Use this scheme for complex turbulent flows.

Bounded Differencing: Provides the Upwind Blending Factor, which specifies the proportion of upwind differencing, $ς_{u b f}$ related to Eqn. (891).; The default value provides the most robustness for the scheme. Reducing it would, in principle, increase accuracy. However, unless you are thoroughly familiar with the theoretical aspects of bounded differencing, do not change this property. The default value reflects optimization for accuracy and performance.

Hybrid-BCD

This scheme blends second-order upwind and bounded-central differencing. This scheme is the default scheme for detached eddy simulation (DES).

As for Bounded-Central.

Reference Values

Maximum Number of Eddies: See Synthetic Eddy Method Reference.

Initial Conditions

Turbulence Specification: Controls how you define the turbulence profile for initialization.; The available methods and corresponding value nodes are equal to the Standard Spalart-Allmaras model, see Spalart-Allmaras Initial Conditions Reference.
Synthetic Turbulence Specification: See Synthetic Eddy Method Reference.

Boundary Settings

Note	Boundary types that do not require setting any conditions or values are not listed.

Flow Boundaries

The following boundary conditions are equal to all boundaries of type:

Free Stream
Mass Flow Inlet
Pressure Outlet
Stagnation Inlet
Velocity Inlet

Turbulence Specification: Controls how you define the turbulence profile at flow boundaries.; The available methods and corresponding value nodes are equal to the Standard Spalart-Allmaras model, see Spalart-Allmaras Boundaries Reference.
Synthetic Turbulence Specification (except Stagnation Inlet and Pressure Outlet): See Synthetic Eddy Method Reference.
Synthetic Turbulence Mass Flow Scaling Specification (except Stagnation Inlet and Pressure Outlet): See Synthetic Eddy Method Reference.

Region Settings

The conditions that are required for each region type that is supported by the Spalart-Allmaras Detached Eddy model are equal to the Standard Spalart-Allmaras model, see Spalart-Allmaras Regions Reference.

Field Functions

The Spalart-Allmaras Detached Eddy model owns the same field functions as the Spalart-Allmaras model, see Spalart-Allmaras Field Functions Reference. The following field functions are specific to the DES version of the model:

DES Low Re Correction Factor: Scalar field that represents the low Reynolds number correction function $ψ$ defined in Eqn. (1411).
DES Upwind Blending Factor: Scalar field that represents the blending function for the hybrid upwind scheme $σ_{H U}$ defined in Eqn. (1450).
Detached Eddy Length Scale: Scalar field that represents the cell length scale that is used for detached eddy simulation, see $Δ$ in Eqn. (1408) and Eqn. (1424).
IDDES Blending Function: Scalar field that represents the blending function ${\tilde{f}}_{d}$ defined in Eqn. (1422) that is used for detached eddy simulation with the IDDES formulation option. This field is only available when you activate the Temporary Storage Retained property of the Spalart-Allmaras Turbulence solver.
IDDES Elevating Function: Scalar field that represents the elevating function $f_{e}$ defined in Eqn. (1415) that is used for detached eddy simulation with the IDDES formulation option. This field is only available when you activate the Temporary Storage Retained property of the Spalart-Allmaras Turbulence solver.
IDDES Length Scale: Scalar field that represents the cell length scale that is used for detached eddy simulation with the IDDES formulation option $Δ_{IDDES}$ , see Eqn. (1424).