Acoustic Wave Model Reference

The Acoustic Wave model is available for three-dimensional unsteady simulations, and with any viscous regime.


Theory	See Acoustic Wave Model.
Provided By	[physics continuum] > Models > Aeroacoustics Models
Example Node Path	Continua > Physics 1 > Models > Acoustic Wave
Requires	Space: Three Dimensional Time: Implicit Unsteady or Explicit Unsteady Material: any but Solid Flow: any Optional Models: Aeroacoustics
Properties	Key property is Noise Source. See also Acoustic Wave Model Properties.
Specific Right-Click Actions	Clear Solution See Specific Right-Click Actions.
Activates	Model Controls (child nodes)	Mean Flow Pressure Reference and Mean Flow Velocity Reference, added when Mean Flow Reference is set to Specified and Enable Convective Acoustic Effects is enabled.
	Materials	See Material Properties.
	Initial Conditions	Acoustic Pressure, Acoustic Pressure Time Derivative, Acoustic Pressure Second Time Derivative. See Initial Conditions.
	Boundary Inputs	See Boundary Settings.
	Region Inputs	See Region Settings.
	Interface Inputs	See Interface Settings.
	Solvers	See Acoustic Wave Solver Properties.
	Monitors	Acoustic Wave
	Field Functions	Acoustic CFL in Wave Equation, Acoustic Pressure See Acoustic Wave Solver Field Function Reference.

The Acoustic Wave model is not compatible with Explicit, Two-Dimensional, or Axisymmetric models. It assumes incompressible flow. The Acoustic Wave model is compatible with stationary cases only—the simulation cannot include any moving regions (such as fan blades).

Note	When you use the Acoustic Wave model, it is recommended that you also activate the Cell Quality Remediation model.

Acoustic Wave Model Properties

Noise Source

Defines the source of acoustic pressure. The specified source is used as the right-hand side of the Acoustic Perturbation Equation (APE) based noise source equation (Eqn. (4713)).

None: No noise source is defined in the flow region. You use this option when you model the acoustic waves that pressure fluctuations generate at a boundary wall.
Acoustic Perturbation Based Source: Models the acoustic waves that the flow pressure fluctuations generate in the fluid flow. This method is the recommended option for hybrid flow and aeroacoustics simulations. For more information, see Setting Up an Acoustic Perturbation-Based Noise Source.
User-Specified Source: Models a user-defined noise source field that then propagates into the domain. This option is used for testing purposes. For more information, see Setting Up a User-Defined Noise Source.

Enable Convective Acoustic Effects

When On, this property includes convection in the simulation. See Acoustic Wave Model theory. When Off, without convection, mean flow pressure is not subtracted from the flow pressure when computing APE-based noise sources.

Low-Pass Time Filtering

Specifies the time filter that is used by the model. Each filter gives the model a low-pass, time-filtered value for the noise source term on the right-hand side of Eqn. (4715). Options other than None also add the Low-Pass Time Filter Cutoff Frequency node under Physics Values for all regions. The default value of the frequency is 1E20 /s.

None: No time filter used.
1st-order IIR: This filter does the least signal damping of the three time filters, and introduces the least phase error. See Eqn. (4716).
2nd-order Butterworth: This filter produces a useful amount of signal damping and only moderate phase error. It is the recommended filter. See Eqn. (4717).
3rd-order Butterworth: This filter gives the most signal damping of the three time filters, but it also produces more phase error. See Eqn. (4718).

Mean Flow Reference

Specifies the method by which the mean pressure and velocity fields are obtained. For more information, see Preliminary Analysis.

Specified: When Enable Convective Acoustic Effects is On, use the velocity field that is specified in the Mean Flow Velocity Reference node and the pressure field that is specified in the Mean Flow Pressure Reference node. These values are typically the Mean of Pressure and Mean of Velocity field functions that are obtained from a fully developed flow solution. For more information, see Preliminary Analysis.
Compute: Compute the mean pressure field with the Acoustic Wave solver already set up to run. With this option, the mean flow calculation starts at time 0 regardless of the time that is specified by the Start Time property of the Acoustic Wave Solver. For more information, see Start Time.

Secondary Gradients

Neglect or include the boundary secondary gradients for diffusion and/or the interior secondary gradients at mesh faces. You can use this option to avoid solution divergence in cases where the Cell Quality Remediation model does not detect and treat bad cells.

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.

Evaluate APE Fields For Post FW-H

When On, the model calculates the following additional fields and makes them available as field functions for far-field noise propagation:

Acoustic Density. See Eqn. (4723).
Acoustic Velocity. See Eqn. (4724).
APE Total Density. See Eqn. (4725).
APE Total Velocity. See Eqn. (4726).
APE Total Pressure. See Eqn. (4727).

See Acoustic Wave Solver Field Functions Reference.

To combine the Acoustic Wave model with the Post FW-H model, use the APE or Flow+APE option for the Acoustic Data Source property of the Post FW-H Post Point Receivers. Store the variables in the .simh file for post-processing.

To combine the Acoustic Wave model with the On-The-Fly FW-H model, use the APE or Flow+APE option for the Acoustic Data Source property of the FW-H Receivers.

When Off, the model does not make the field functions available. This is the default.

Recon Gradient Smoothing Passes

The number of passes the model makes with a smoothing algorithm over the acoustic pressure reconstruction gradient. Set the value to zero to forego using the smoothing algorithm. The default is 2.

Specific Right-Click Actions

Clear Solution: Causes all storage that is associated with the solution to be cleared from memory of the computer, just as with the Solution > Clear Solution... menu selection.

Material Properties

Speed of Sound

The speed of sound in the far-field,

c_{0}

in Eqn. (4659).


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 $M$ . Specific Heat 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 $M$ . Specific Heat Specifies the specific heat capacity $C_{p}$ .

Initial Conditions

Acoustic Pressure: The value $p^{a}$ that is used in the Acoustic Perturbation Equation (Eqn. (4713)).
Acoustic Pressure Second Time Derivative: The second time derivative of acoustic pressure, $\frac{\partial^{2} p^{a}}{\partial t^{2}}$ .   This value is used for the Newmark solver.
Acoustic Pressure Time Derivative: The first time derivative of acoustic pressure, $\frac{\partial p^{a}}{\partial t}$ .   This value is used for the Newmark solver.

You do not need to set these initial conditions in a typical acoustic wave simulation. However, you can use particular settings for testing purposes.

For more information on the corresponding field functions, see Acoustic Wave Solver Field Functions Reference.

Boundary Settings

Symmetry Plane

Symmetry Acoustic Pressure Specification: When On, the symmetry plane boundary is non-reflecting; acoustic waves pass through the boundary. When Off, the symmetry plane boundary remains a symmetry condition and is also reflecting boundary. The default is Off.

Wall

Wall Acoustic Pressure Specification

Overall description of this condition node.

Method	Corresponding Physics Value Nodes
None The wall boundary has no specific acoustic pressure but is a reflecting boundary.	None
Specified Sets the value of acoustic pressure at the wall directly.	Prescribed Acoustic Pressure Sets the value using common methods for a scalar profile.
Non-reflecting The wall is a non-reflecting boundary. Acoustic waves pass through the boundary.	None
Partially Absorbing Sets the fraction of the pressure absorbed at the wall to a value between 0 and 1.	Partial Wall Absorption Coefficient Sets the value using common methods for a scalar profile.

All other boundaries

Prescribed Acoustic Pressure Specification: Sets the value for acoustic pressure using common methods for a scalar profile.

Region Settings

Applies to fluid regions.

Acoustic Damping Coefficient: Sets the value using common methods for a scalar profile.
Noise Source Weighting Coefficient: Sets the value using common methods for a scalar profile.
User Defined Noise Source: Sets the value using common methods for a scalar profile. Available when the Noise Source property is set to User-Specified 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 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

The Acoustic Wave solver is activated when the Acoustic Wave model is selected. 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.
If the Mean Flow Reference property in the Acoustic Wave model is set to Compute, use the Start Time property to specify a start time delay, to minimize initial transient flow effects into the mean flow fields. The time that is required depends on the simulation parameters, particularly the geometry and the flow velocity. A reasonable guideline is to allow a delay time of ten flow-through periods. By default, the solver starts with a five time-step delay (if the start time is set to 0.0 s) in order to pre-compute the noise source time derivative.
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. (4722).

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.