Working with FW-H Receivers

FW-H Receivers Properties

Far-Field Density

The density of the far-field fluid. The default value is 1.225 kg/m³.

Far-Field Sound Speed

The sound speed in the far-field. See Eqn. (4659)

The default value is 340 m/s.

Acoustic Correlation Length

Sets the correlation length to include spanwise correlation of the flow over a finite span, for two-dimensional simulations only. It repeats the 2D domain in the third direction with a limited number of cells, the number based on correlation length value. The solver takes the source data from the XY plane segment and copies it into an array that corresponds to the full extent, then applies the FW-H solver on this new source sound data set.

Acoustic Data Source

Sets the data source for the On-the-Fly model.

Flow

The On-the-Fly FW-H model uses the flow field variables pressure, density, and velocity of the compressible or incompressible flow, provided by the segregated or coupled flow solver. This is the default.

• FW-H pressure $=\mathrm{\Sigma }{P}_{fwh}=P_f$
• FW-H density $=\mathrm{\Sigma }{\rho }_{fwh}={\rho }_f$
• FW-H velocity $=\mathrm{\Sigma }{\mathbf{v}}_{fwh}={\mathbf{v}}_f$

Flow+APE

The On-the-Fly FW-H model uses the following variables of the incompressible flow from the Acoustic Wave model:

• FW-H pressure $=\mathrm{\Sigma }{P}_{fwh}=P_a+P_f$
• FW-H density $=\mathrm{\Sigma }{\rho }_{fwh}=\frac{P_a}{c^2}+{\rho }_f$
• FW-H velocity $=\mathrm{\Sigma }{\mathbf{v}}_{fwh}={\mathbf{v}}_a+{\mathbf{v}}_f$

APE

The On-the-Fly FW-H model uses the following variables of the incompressible flow from the Acoustic Wave model or the Perturbed Convective Wave model:

• FW-H pressure $=\mathrm{\Sigma }{P}_{fwh}=P_a$
• FW-H density $=\mathrm{\Sigma }{\rho }_{fwh}=\frac{P_a}{c^2}+{\rho }_f$
• FW-H velocity $=\mathrm{\Sigma }{\mathbf{v}}_{fwh}={\mathbf{v}}_a$

Where:

• $P_f$ is the pressure of the compressible or incompressible flow.
• ${\rho }_f$ is the density of the compressible or incompressible flow.
• ${\mathbf{v}}_f$ is the velocity of the compressible or incompressible flow.
• $P_a$ is the acoustic pressure provided by the Acoustic Wave model or the Perturbed Convective Wave model.
• $c$ is the speed of sound.
• ${\mathbf{v}}_a$ is the acoustic velocity.

Point Receivers

A point receiver is a point inside or outside the domain (located in the mid- to far-field), where the sound pressure is predicted. The total acoustic signal that is measured at a receiver is the sum of the acoustic signals that are radiated from each source element of the FW-H surfaces. A point receiver is represented by a node in the object tree.

If more than one of these objects are added to the simulation, then the second and subsequent ones have numbers at the end of the labels. You can define many receivers, each with a specific FW-H surface that can be monitored.

Receivers can be renamed, copied, and deleted in the same way as other simulation objects. Each receiver has a child node for an associated table. This node always has the same name as the receiver and is renamed, copied, and deleted with it. The table contains the pruned acoustic data for Acoustic Time, Sound Pressure Surface Total, Sound Pressure Loading Noise, Sound Pressure Thickness Noise Quadrupole Acoustic Time, Quadrupole Sound Pressure.

Creating Point Receivers

To add a point receiver to the simulation, right-click the FW-H Receivers manager node and select New Point Receiver. Set the properties.

To display the point receiver, open the associated scene, then open the FW-H Receivers node and select the node for that point receiver.

Pop-Up Menu of the FW-H Receivers Manager

New Point Receiver

Adds a point receiver to the object tree.

Clear Receivers

Clears the acoustic recorded data of all the point receivers.

Point Receiver Properties

Index

Index reference for the point receiver (read-only).

Position

The position of the receiver.

FW-H Surface

Selects which FW-H surface to watch from a drop-down list of surfaces in the simulation. Only one of these surfaces (impermeable or permeable) can be selected at a time for each point receiver, though each surface can contain multiple boundaries.

FW-H Formulation

Selects the formulation to use for the surface terms.

Farassat_1A

Uses Farassat's Formulation 1A, Eqn. (4760) and Eqn. (4761). This is the default formulation.

Dunn_Farassat_Padula_1A

Uses the Dunn-Farassat-Padula Formulation 1A, Eqn. (4762) and Eqn. (4763).

Coordinate System

Combined with the setting for the Position property, your selection of a local coordinate system permits definition of the point location of the receiver.

Regions

Defines the regions or user-defined volumes to contribute to the computation of quadrupole noise. By default, no regions are selected.

Point Receiver Pop-Up Menu

Clear Receiver

Clears the acoustic recorded data of the point receiver.

Point Receiver Table Node Properties

Below each point receiver node is a node for the table associated with the point receiver that contains the pruned acoustic data.

Extracted

Lists extracted data sets.

Point Receiver Table Node Pop-Up Menu

Receiver noise data is stored under the point receiver nodes in table nodes named after the receivers.

Export...

Opens the Save dialog, in which you can specify the location for the exported data set.

Extract

Extracts the data sets, which are then listed under the Extracted property.

Tabulate...

Displays the Tabular Data window, which gives you the option to export the data.

Clearing Point Receiver Data

To clear the solution data of the point receivers, right-click the FW-H Receivers manager node and select Clear Receivers.

Exporting Point Receiver Data

To export the solution data of a point receiver, right-click the table node of that receiver and select one of the export options.

This action opens a standard dialog for you to save the data of the receiver as a .csv file in a location of your choice.

For each type of export, the sound pressure data is pruned before export, which effectively clips the receiver data at the beginning and end of the collection time to ensure that all faces on all the source surfaces were contributing to the received data. The pruning accounts for the fact that signals from source surface faces closest to the receiver arrive before signals from faces furthest from the receiver. To account for this pruning of exported data, run the case for a longer period.