# writing an acoustic code based on FW-H equation, have a question regarding pressure

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May 8, 2011, 08:26
writing an acoustic code based on FW-H equation, have a question regarding pressure
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Join Date: Jul 2010
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Dear Foamers,

I'm writing a code based on Ffowcs William- Hawkings (FW-h) equation. I just have one question.

As we know the formulation of Fw-h equation is like the first attached file.

The question is: As I know and read in some references the term P0 ( in the equation) is the pressure of the air(for example) at the rest or far field. But someone told me that it is the pressure of the mean flow, that means (P-P0) represents fluctuating pressure. For example suppose a fan that repeat its cycle and we get average of these cycles and calculate P0 and so calculate (P-P0) from this method. (see second attached file)

So, (P-P0) is equal to :
unsteady pressure - constant far-field pressure?!

Attached Images
 FW-H.png (30.5 KB, 76 views) question.png (12.0 KB, 63 views)

 April 13, 2013, 07:01 #2 Senior Member     Hasan K.J. Join Date: Dec 2011 Location: Bristol, United Kingdom Posts: 200 Rep Power: 14 Hello Reza, Have u made this model yet by anychance and how did your validation go, i am very interested in your model thanks, hasan.

 February 13, 2014, 19:55 #3 Senior Member   ArathoN Join Date: Jul 2011 Posts: 137 Rep Power: 14 I'm interested too in this subject. By the way P0 is the reference pressure and only in the condition of low Mach number (so low perturbation) you can consider that the P0 is equal to the mean pressure hence the acoustical pressure perturbation is equal to the perturbation relative to the turbulence.

 November 8, 2014, 20:12 #4 New Member   patrick okolo Join Date: Nov 2011 Posts: 14 Rep Power: 13 Hi Guys, Was any of you successful in implementing the FW-H analogy in OpenFoam ?? please i need help in it.