Setting Up an On-the-Fly FW-H Simulation

Before using the On-the-Fly FW-H model, first solve your unsteady simulation for noise sources in the near-field using the aeroacoustics recommended analysis procedure.

To set up an On-the-Fly FW-H simulation:
  1. Add the On-the-Fly FW-H model and the FW-H Unsteady Solver to your analysis.
    注For quasi-steady rotating machines, use the Ffowcs Williams-Hawkings Steady model and the FW-H Steady Solver.
  2. Create FW-H surfaces. See Creating FW-H Surfaces.
  3. For each FW-H surface, specify the relevant source boundaries. See Impermeable FW-H Surfaces and Permeable FW-H Surfaces.
    For Permeable FW-H surfaces, make sure that you select as source boundary the side of the interface that has surface normal pointing inwards (that is, opposite the direction of sound propagation). To check the surface normal direction:
    1. In a vector scene, plot the Area field function on both boundaries of the internal interface.
    2. If the source boundary that you selected for the FW-H surface does not have the correct surface normal, choose the other side of the interface as source boundary.
  4. Create FW-H receivers and associate each with an FW-H surface. Highlight the receivers and double-check the locations.
  5. Set the FW-H Unsteady Solver properties, especially the time when receivers start collecting data.
  6. If desired, set up quadrupole noise calculation:
    1. Select the On-the-Fly model and activate the Quadrupole Noise property.
    2. Select the volume sources of noise: select the Region property of each point receiver and select the list of regions generating the volumetric quadrupole noise. By default, no regions are selected.
    When the simulation runs, the model calculates the quadrupole noise using the collapsing sphere formulation, based on the selected volume distribution of the noise sources. Receiver noise data is stored under FW-H Receivers > [point receiver] > [point receiver table], in table nodes named after the receivers.
  7. As the memory consumption for storing receiver noise data increases linearly with the number of receivers and time-steps, monitor the memory consumption and automatically stop the simulation when 80% of your available memory is exceeded:
    1. Set up the auto save feature to save the simulation at regular intervals. See Automatically Saving at Regular Intervals.
    2. Right-click the Reports node and select New > System > Maximum Memory Report.
    3. Select the Maximum Memory Report node and make sure that Metric Type is set to Resident.
    4. Right-click the Maximum Memory Report node and select Create Monitor and Plot from Report.
    5. Right-click the Monitors > Maximum Memory Report Monitor node and select Create Stopping Criterion from Monitor.
    6. Edit the Stopping Criteria > Maximum Memory Report Monitor Criterion node and set the following properties:
      PropertySetting

      Criterion Option

      Maximum

      Stop Inner IterationsDeactivated
      Maximum Limit > Maximum ValueSet the value to 80% of the memory available on your computer.
    If the memory usage of your simulation exceeds 80% of your computer memory, you are advised to reduce the number of receivers or to use the Post FW-H Model instead.
  8. If desired, set up a plot of acoustic time versus sound pressure surface total:
    1. Create a new plot, usually an XY plot. See XY 绘图工作流程.
    2. Expand the plot node, right-click Data Series, and select Add Data.
    3. In the Add Data Provider to Plot dialog, expand the FW-H Receiver > [point receiver] node and select the relevant [point receiver table] node.
    Alternatively, create a new plot, then drag the point receiver Table node onto the plot window.
  9. If desired, create a data set function:
    1. Right-click on Tools > Data Set Functions > G(p) 1 > Tabular and select New derived data from table.
      A new node appears under Tabular.
    2. Select the Tabular > [data derived from a table] node and set the following properties:
      PropertySetting
      Input Data 1FW-H Receivers > [point receiver] > [point receiver table]
      X Column 1Independent variable, usually Acoustic Time
      Y Column 1Dependent variable, usually Sound Pressure Surface Total
      Update ActivateOn

Using Volume Sources for Quadrupole Noise

The On-the-Fly model can compute quadrupole noise contributions for specified volumes. Use this feature when you want to:

  • Compute the quadrupole noise contribution from specific region.
  • Compare quadrupole noise contributions from different regions.
  • Compute quadrupole noise from combinations of regions.
  • Visualize the Quadrupole Volume Term field function to see the location of the quadrupole sources.

See Visualizing the FW-H Noise Sources.