Lighthill Wave Model Reference

The Lighthill Wave model computes the Lighthill pressure, which represents the sum of the acoustic pressure and the hydrodynamic pressure. It allows you to simulate noise that is generated by the flow of an incompressible fluid at low Mach numbers ( $M a < 0.2$ ).


Theory	See Lighthill Wave Model.
Provided By	[physics continuum] > Models > Aeroacoustics Models
Example Node Path	Continua > Physics 1 > Models > Lighthill Wave
Requires	Space: Three Dimensional Time: Implicit Unsteady Material: any but Solid or Multi-Component Solid Flow: any Equation of State: Constant Density Optional Models: Aeroacoustics
Properties	See Lighthill Wave Properties.
Activates	Materials	See Material Properties.
	Boundary Inputs	See Boundary Settings.
	Region Inputs	See Region Settings.
	Interface Inputs	See Interface Settings.
	Solvers	Acoustic Wave See Acoustic Wave Solver Properties.
	Field Functions	Lighthill Pressure Lighthill Source See Field Functions.

Lighthill Wave Properties

Secondary Gradients

Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces.

On: Include both secondary gradients.
Off: Exclude both secondary gradients.
Interior Only: Include the interior secondary gradients only.
Boundaries Only: Include the boundary secondary gradients only.

Material Properties

Speed of Sound

The speed of sound in the far-field,

c_{0}

in Eqn. (4730).


Method	Corresponding Method Node
Constant Specifes the speed of sound using a scalar profile value.	Constant Specifies the speed of sound $c_{0}$ .
Ideal Gas (Density and Reference Pressure) Calculates the speed of sound using the ideal gas law as: $c_{0} = \sqrt{\frac{γ p_{0}}{ρ}}$ with: $γ = \frac{C_{p}}{(C_{p} - \frac{R}{M})}$ where: $p_{0}$ is the reference pressure $ρ$ is the density. $C_{p}$ is the specific heat capacity. $R$ is the universal gas constant. $M$ is the molecular weight.	Ideal Gas (Density and Reference Pressure) This node provides no properties. Selecting this method adds the following material property: Molecular Weight Specifies the molecular weight $M$ . Heat Capacity Specifies the specific heat capacity $C_{p}$ .
Ideal Gas (Reference Temperature) Calculates the speed of sound using the ideal gas law as: $c_{0} = \sqrt{γ R T_{0}}$ with: $γ = \frac{C_{p}}{(C_{p} - \frac{R}{M})}$ where $T_{0}$ is the reference temperature.	Ideal Gas (Reference Temperature) Exposes the following property: Reference Temperature Specifies the reference temperature $T_{0}$ . Selecting this method adds the following material property: Molecular Weight Specifies the molecular weight $M$ . Heat Capacity Specifies the specific heat capacity $C_{p}$ .

Boundary Settings

Wall

Wall Acoustic Pressure Specification

Specifies how the wall boundary acts on the Lighthill pressure.

Option	Corresponding Physics Value Nodes
None The wall boundary has no specific Lighthill pressure but is a reflecting boundary.	None
Non-reflecting The wall is a non-reflecting boundary. Lighthill waves are absorbed at the boundary.	None
Partially Absorbing The wall boundary partially absorbs the Lighthill pressure.	Partial Wall Absorption Coefficient Specifies the fraction of Lighthill pressure that is absorbed at the boundary as a value between 0 and 1.

Symmetry Plane

Symmetry Acoustic Pressure Specification

Specifies how the symmetry plane boundary acts on the Lighthill pressure.

Non-reflective boundary condition treatment	Corresponding Physics Value Nodes
On The symmetry plane boundary is non-reflecting. Lighthill waves are absorbed at the boundary.	None
Off The symmetry plane boundary is a reflecting boundary.	None

Flow Boundaries

The following boundary condition is available for all boundaries of type:

Mass Flow Inlet
Stagnation Inlet
Velocity Inlet
Pressure Outlet
Outlet

Prescribed Acoustic Pressure Specification

Specifies how the flow boundary acts on the Lighthill pressure.

Prescribed boundary condition	Corresponding Physics Value Nodes
On Sets a specified Lighthill pressure at the boundary.	Prescribed Acoustic Pressure Specifies the Lighthill pressure at the boundary.
Off The flow boundary is a non-reflective boundary. Lighthill waves are absorbed at the boundary.	None

Region Settings

Applies to fluid regions.

Acoustic Damping Coefficient: $b_{d}$ in Eqn. (4732) (0 for no damping and 1 for maximum damping).
Noise Source Weighting Coefficient: $b_{s}$ in Eqn. (4731) (1 for computing the noise source and 0 for removing the noise source).

Interface Settings

Applies to porous baffle interfaces.

Porous Baffle Acoustic Option

Specifies how the porous baffle interface acts on acoustic waves.


Porous Baffle Acoustic Option	Corresponding Physics Value Nodes
Reflecting Acoustic waves reflect from the porous baffle interface interface as they reflect from a solid wall. The acoustic source terms are calculated assuming zero velocity at the interface.	None
Transparent Acoustic waves travel through the porous baffle interface as they travel through an internal interface. No reflections occur. The sound sources are calculated assuming a continuous, smooth velocity field across the interface.	None

Acoustic Wave Solver Properties

Similar to the flow solvers, the Acoustic Wave solver uses the AMG Linear Solver infrastructure that is provided in Simcenter STAR-CCM+.

Acoustic Wave

Start Time: The elapsed simulation time before the solver begins calculating.
Number of acoustic time steps per flow time step: The number of acoustic wave solver time-steps that are computed at each flow time-step.
Number of acoustic inner iterations: Maximum number of inner iterations executed by the Acoustic Wave solver.
Convergence tolerance: The acoustic solver convergence limit to break out of the inner iterations. Typically, a value of 3-4 orders of magnitude of the normalized acoustic solver residual.
Minimum convergence tolerance: Absolute convergence criterion. The maximum value between the convergence tolerance and the minimum convergence tolerance is taken as the final convergence tolerance.
Verbosity: When On, prints the acoustic solver residuals in the output window. The default is Off.
Reconstruction Frozen: When On, Simcenter STAR-CCM+ does not update reconstruction gradients with each iteration, but rather uses gradients from the last iteration in which they were updated. Activate Temporary Storage Retained in conjunction with this property. This property is Off by default.
Reconstruction Zeroed: When On, the solver sets reconstruction gradients to zero at the next iteration. This action means that face values used for upwinding (Eqn. (905)) and for computing cell gradients (Eqn. (917) and Eqn. (918)) become first-order estimates. This property is Off by default. If you turn this property Off after having it On, the solver recomputes the gradients on the next iteration.
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, Simcenter STAR-CCM+ retains additional field data that the solver generates during an iteration. The particular data retained depends on the solver, and becomes available as field functions during subsequent iterations. Off by default.

Acoustic Wave > Newmark Alpha Parameter

Specifies a weighting parameter for the Newmark Alpha method of numerical integration,

α

in Eqn. (4734). Use non-zero values of

α

in the range

- 0.33 \leq α \leq 0

to damp spurious high frequencies. The default value is -0.05.

Field Functions

Lighthill Pressure: $p^{l}$ in Eqn. (4730).
Lighthill Source: $\nabla\cdot h$ in Eqn. (4730).; This field is only available when Temporary Storage Retained is activated for the Lighthill Wave solver.