Setting Up a Lighthill Wave Simulation

The analysis of noise propagation using the Lighthill Wave model requires an unsteady scale-resolving simulation of an incompressible fluid within a three-dimensional flow domain.

In addition to the requirements for a scale-resolving simulation, to maintain the accuracy of the acoustic predictions, you are advised to apply a criterion for points per wavelength (PPW) when generating the mesh.

PPW is defined as:

P P W = \frac{c / f}{Δ x}

(273)

where $c$ is the speed of sound and $f$ is the frequency of the waves you want to resolve.

The recommended PPW for a simulation using the Lighthill Wave model is ≥15 PPW.

Therefore limit the cell size as:

Δ x \leq \frac{c / f}{15}

(274)

Note	You are advised to run a Lighthill Wave simulation using a double-precision version of Simcenter STAR-CCM+.

To set up an aeroacoustics simulation using the Lighthill Wave model:

Create a physics continuum and assign it to the flow region.

In the physics continuum, deactivate Auto-select recommended models, then select the following models in order:


Group Box	Model
Space	Three-Dimensional
Time	Implicit Unsteady
Material	Any except Solid or Multi-Component Solid
Flow	Any
Equation of State	Constant Density
Viscous Regime	Turbulent
Turbulence	Detached Eddy Simulation or Large Eddy Simulation For more information, see Scale-Resolving Simulations.
Optional Models	Aeroacoustics
Aeroacoustics Models	Lighthill Wave

Set up the boundaries in the flow region.
The Lighthill Wave model supports the following boundary types: Wall, Symmetry Plane, Inlet, Outlet, and Periodic.
See Lighthill Wave Model Reference—Boundary Settings.
For porous baffle interfaces in your flow domain, specify whether acoustic waves reflect from the interface or travel through it.
See Lighthill Wave Model Reference—Interface Settings.
Set up the Acoustic Wave solver:
- Use implicit time marching with sufficient inner iterations to ensure convergence.
- For the time step-size $Δ t$ , to resolve the wave amplitude in a Lighthill Wave simulation, you are advised to use ≥15 time-steps per period.
  Therefore, limit the time-step size as:
  
  $Δ t \leq \frac{1 / f}{15}$
  
  (275)
- To reduce spurious noises, select the Newmark Alpha Parameter node and set the value slightly lower than the default of -0.05. The allowed range is $- 1 / 3 \leq α \leq 0$ . For simulations with rotating geometries, you are advised to set a value of -1/3.
  See Lighthill Wave Model Reference—Acoustic Wave Solver Properties.
Set up the necessary stopping criteria, derived parts, and reports.
Create probes for acoustic pressure monitoring in the region of interest. Simcenter STAR-CCM+ provides built-in data set functions, such as Fourier Transforms, that you can use to apply signal processing to the acoustic data. For more information, see Using Data Set Functions.
Run the simulation to obtain the Lighthill pressure values in the flow region.