[Rinia]

Hey, CFDers

I am performing a simulation about the unmanned drone propeller with compresible LES. The instantaneous pressure fluctuation is obtain by subtracting the time-average pressure from the pressure.

I would to know if the pressure fluctuation obtained in this way contains the turbulence and acoustic compent, and if it is possible to obtain acoustic pressure fluctuation only?

Thank you in advance.

[FMDenaro]

Originally Posted by Rinia

Hey, CFDers

I am performing a simulation about the unmanned drone propeller with compresible LES. The instantaneous pressure fluctuation is obtain by subtracting the time-average pressure from the pressure.

I would to know if the pressure fluctuation obtained in this way contains the turbulence and acoustic compent, and if it is possible to obtain acoustic pressure fluctuation only?

Thank you in advance.

You get the fluctuations only from the resolved LES field.
They are not exactly as same as in case of a DNS.

[LuckyTran]

To clarify, yes they do contain the acoustic and the turbulence fluctuations. But... LES is spatially filtered. The filtered variables only contains the filtered parts of the fluctuations. There are fluctuations at the sub-filter scale which are not included in the filtered velocities which you need to also add if you want to account for fluctuations at all scales.


The acoustic component you can get by ensemble averaging the pressure results; more generally, you would apply a temporal filter. Turbulence is random so the ensemble average will eliminate them. It's also sometimes called a phase average. Note that there are as many ensemble averages as there are ensembles. Ensemble averaging is feasible if you know a priori which specific frequencies are of interest so you can average only those ensembles, otherwise you have an infinite number of them.