LES and Subgrid Scale Turbulence Models Reference

Models Overview


Model Names and Abbreviations	Dynamic Smagorinsky Subgrid Scale		DS SS
	Smagorinsky Subgrid Scale		S SS
	WALE Subgrid Scale*		W SS
Theory	See Theory Guide—Large Eddy Simulation.
Provided By	[physics continuum] > Models > Subgrid Scale Turbulence
Example Node Path	Continua > Physics 1 > Models > Dynamic Smagorinsky Subgrid Scale
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 Flow: any Viscous Regime: Turbulent Turbulence: Large Eddy Simulation
Properties	See Properties Lookup.
Activates	Physics Models	Wall Distance: Wall Distance*
		Wall Treatment: All y+ Wall Treatment and Low y+ Wall Treatment
		Optional Models: Anisotropic Linear Forcing
	Methods	Convection See Methods.
	Reference Values	Maximum Number of Eddies See Reference Values.
	Initial Conditions	Synthetic Turbulence Specification See Initial Conditions.
	Boundary Inputs	Synthetic Turbulence Specification Synthetic Turbulence Mass Flow Scaling Specification See Boundary Settings.
	Solvers	Dynamic Smagorinsky SGS Viscosity (DS SS) Smagorinsky SGS Viscosity (S SS) WALE SGS Viscosity (W SS) See SGS Viscosity Solvers.
	Field Functions	SGS Wall Damping Factor (S SS) Turbulent Viscosity Turbulent Viscosity Ratio See Field Functions.

Properties Lookup

This table shows which properties are used by which Subgrid Scale model. Use the abbreviations that are given in the Models Overview above.

Unless you are thoroughly familiar with the theoretical aspects of this model and the discretization techniques used in Simcenter STAR-CCM+, we recommend that you not make any changes within the Expert category. The values in that category reflect both the model’s design and discretization approaches that have been optimized for accuracy and performance. Tampering with them may diminish the effectiveness of the model.


	DS SS	S SS	W SS
A Van Driest damping coefficient, Eqn. (1389).
Average Parameter When On, uses averaging in calculation of $C_{s}^{2}$ (see Eqn. (1396)).
Cs The coefficient $C_{s}$ in Eqn. (1388).
Ct The coefficient $C_{t}$ in Eqn. (1495).
Cw The coefficient $C_{w}$ in Eqn. (1398).
Filter Width Ratio Ratio of test filter width to grid filter width $\frac{\hat{L}}{\tilde{L}}$ in Eqn. (1395).
Kappa The von Karman constant $κ$ in Eqn. (1388) (S SS) and in Eqn. (1398) (W SS).
Limit Length Scale When On, the mixing length minimum is applied to the subgrid scale viscosity, see Eqn. (1388) (S SS) and Eqn. (1398) (W SS).
Minimum Cs^2 Value Clips values less than the specified value of $C_{s}^{2}$ (see Eqn. (1396)).
Maximum Cs^2 Value Clips values greater than the specified value of $C_{s}^{2}$ (see Eqn. (1396)).
Van Driest Damping Selects the Van Driest damping function, see Eqn. (1389): None: No damping. Original: Van Driest’s original damping function. Modified: Van Driest’s damping function modified according to Piomelli and co-workers [351].

Methods

Convection

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

Method	Corresponding Method Node
Central This scheme is second-order accurate but is prone to dispersive error and stability problems. However, central-differencing is useful in large eddy simulations where upwind schemes accelerate the rate at which turbulent kinetic energy decays.	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.

Method

Corresponding Method Node

Central

This scheme is second-order accurate but is prone to dispersive error and stability problems. However, central-differencing is useful in large eddy simulations where upwind schemes accelerate the rate at which turbulent kinetic energy decays.

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.

Reference Values

Maximum Number of Eddies: See Synthetic Eddy Method Reference.

Initial Conditions

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
Velocity Inlet

Synthetic Turbulence Specification: See Synthetic Eddy Method Reference.
Synthetic Turbulence Mass Flow Scaling Specification: See Synthetic Eddy Method Reference.

SGS Viscosity Solver Properties

This section describes the solver that updates the subgrid scale viscosity $μ_{t}$ in all the continua for which the subgrid scale model is activated. Since subgrid scale models do not contain any transport equations, there are no other solvers associated with the models.

Damping Factor Update Policy (S SS)

Controls the policy for updating the damping factor:

Time Step: Updates will be triggered on a per time-step basis.
Iteration: Updates will be triggered on a per iteration basis.

Damping Factor Update Frequency (S SS)

This parameter governs the frequency at which the damping factor

f_{v}

will be updated in the free stream. The default is 1, which means that the update occurs every iteration. Increasing this parameter to a larger interval, say 10, might improve parallel performance in certain situations. This is because the free-stream values are stored in a KD tree that is broadcast to each parallel node. incurring a communication overhead.

Solver Frozen

When On, the solver does not update any quantity during an iteration. It is Off by default. This is a debugging option that can result in non-recoverable errors and wrong solutions due to missing storage. See Finite Volume Solvers Reference for details.

Temporary Storage Retained

When On, retains temporary storage at the end of the iteration. Examples include the

a p

coefficients, the residual, the corrections, the reconstruction gradients and the cell gradients. These quantities will become available as field functions during subsequent iterations. This property if Off by default.

Field Functions

SGS Turbulent Kinetic Energy: Subgrid kinetic energy, $k_{S G S}$ in Eqn. (1497).; When you activate a model that uses SGS length/time/velocity scales (such as a Ffowcs Williams-Hawkings Model) along with a subgrid scale model, this field function is available by default.; Otherwise, this field function is only available when you activate the Temporary Storage Retained option for the SGS Viscosity solver.
SGS Wall Damping Factor (S SS): Scalar field that represents the Van Driest damping function $f_{v}$ defined in Eqn. (1389).
Turbulent Viscosity: Scalar field that represents the turbulent viscosity $μ_{t}$ .
Turbulent Viscosity Ratio: Scalar field that represents the ratio of turbulent to laminar viscosity $μ_{t} / μ$ .