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Aeroacoustics – Negative Decibels

- March 19, 2024 at 10:01 pm
  
  Jack Spreadbury
  Subscriber
  
  Hi,
  I'm conucting a 2D aeroacoustic analysis of a NACA0012 Aerofoil as part of an experimental validation task.
  Using the LES model, I achieve sensible results (within +/- 5dB of the experimental values).
  However, when using URANS (k-omega SST) I'm getting negative SPLs across the entire frequency spectrum (-70dB to -98dB).
  Has anyone encountered this problem before, if so, is there any advice on how to fix this?
  Cheers
- March 20, 2024 at 4:50 pm
  
  Federico
  Ansys Employee
  
  Hello Jack,
  negative Sound Pressure Level indicates that the pressure fluctuations being simulated are lower than the reference pressure used to calculate SPL, so your results would suggest that you may not be resolving those pressure fluctuations.
  Are you using the same mesh and time step size for both cases?
- March 20, 2024 at 5:55 pm
  
  Jack Spreadbury
  Subscriber
  
  Hi,
  Yes, an identical mesh was used, hence the confusion. I predicted a drop off in accuracy between LES and URANS but not as significant as this. Just wandering if there is any advice on how to fix this. The same reference pressure (default) was used for both.

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