Speed of sound (mesh movement)

AliAli · October 15, 2009, 04:07

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, 07:35

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, 10:12

Hallo,

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=(K/density)^0.5

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, 19:48

Can you post your CCL?

AliAli · October 16, 2009, 05:29

Hallo,
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,

Thanks

ghorrocks · October 18, 2009, 08:12

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

October 15, 2009, 04:07	Speed of sound (mesh movement)	#1
AliAli New Member Ali Join Date: Oct 2009 Posts: 9 Rep Power: 17	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.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
CrankNicholson returns wrong dimensions and sound speed when mesh is moving	lillberg	OpenFOAM Bugs	6	May 4, 2009 18:53
Abt: the speed of sound in incompressible flows	jinwon park	Main CFD Forum	3	August 21, 2008 21:44
ICEM 10 mesh question	DAK565656	CFX	6	May 8, 2007 13:16
How to execute a bidirectional mesh movement( FSI)	Ganesan	CFX	0	April 19, 2007 09:01
Icemcfd 11: Loss of mesh from surface mesh option?	Joe	CFX	2	March 26, 2007 19:10

October 15, 2009, 07:35		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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.

October 15, 2009, 10:12		#3
AliAli New Member Ali Join Date: Oct 2009 Posts: 9 Rep Power: 17	Hallo, 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=(K/density)^0.5 C: speed of sound (1500 m/s) in water. I used constant value. K: Bulk modulus, function of pressure. Any suggestions or ideas??

October 15, 2009, 19:48		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Can you post your CCL?

October 16, 2009, 05:29		#5
AliAli New Member Ali Join Date: Oct 2009 Posts: 9 Rep Power: 17	Hallo, 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, Thanks

October 18, 2009, 08:12		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	No, post the entire CCL. I don't have the time or inclination to check people's def files.