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AliAli October 15, 2009 03:07

Speed of sound (mesh movement)
I used bulk modulus approach for defining the density for the model of piston movement.The bulk modulus is as a function of pressure (table below), then I used an expression for calculating densiyt as a function of variable bulk modulus and constant speed of sound (1500 m/s). Table: bulk modulus versus pressure at 68 F degree for water (from fluid mechanics book)

Pressure (Psi) Bulk modulus (Psi)
.................. ........................
15 ------------320,000
1,500 -------- 330,000
4,500 ---------348,000
15,000 --------410,000

But, from the slover, i observed that the speed of sound is equal to (578) in the average scale information, i think that is not true. Could someone help please? if it is not the right way for defining the bulk modulus apporach, could someone tell me how to define it??? Thanks in advance.

ghorrocks October 15, 2009 06:35

Sounds like your density/pressure function is wrong. Or the average scale information is misleading you. Check in detail in CFD-Post what the acoustic velocity is.

AliAli October 15, 2009 09:12


Thanks for your answer. I cheked the wave's velocity in post, it is also 578 (m/s). The density/pressure function that I used is:


C: speed of sound (1500 m/s) in water. I used constant value.
K: Bulk modulus, function of pressure.

Any suggestions or ideas??

ghorrocks October 15, 2009 18:48

Can you post your CCL?

AliAli October 16, 2009 04:29

Here is the expression:

(BulkModulus(Absolute Pressure))/((1500 [m/s]*1500 [m/s]))

BulkModulus: is function of pressure for the table in my post messege 1.

I could also send you the definition files, if you have time to have a look, please just give me you email address,


ghorrocks October 18, 2009 07:12

No, post the entire CCL. I don't have the time or inclination to check people's def files.

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