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-   -   Incompressible Ideal gas law (http://www.cfd-online.com/Forums/fluent/50614-incompressible-ideal-gas-law.html)

Leverkin February 19, 2009 09:05

Incompressible Ideal gas law
 
Hello dear people,

I would like to ask about the incompressible ideal gas law. As i have understood, and please correct me if I am mistaken, when you use the incompressible ideal gas law the fluid is incompressible due to the low mach number but depends from the temperature variations.

What happens then to the density in the continuity equation? Is it still removed from the equation (because it is incompressible) and it is

grad(V) = 0?

or Fluent solves grad(ρV) = 0 and it is taking account of the density variations from the temperature?

Thanks in advance

Suresh kumar February 20, 2009 06:51

Re: Incompressible Ideal gas law
 
It solves grad(ρV) = 0 and it is taking account of the density variations from the temperature by calculating gas equation.In transient cases, time also plays role.


Leverkin February 20, 2009 09:54

Re: Incompressible Ideal gas law
 
Thank you very much for your reply. So the name "incompressible" is not accurate since it's solving grad(ρV)=0.

Again thank you for your reply.

Best.

Ralf Schmidt February 23, 2009 05:52

Re: Incompressible Ideal gas law
 
the fluid is incompressible, because it can not be compressed by pressure. So density depends only on temperature

Ralf

Leverkin March 3, 2009 10:57

Re: Incompressible Ideal gas law
 
Yes i agree with you. But the term incompressible is used only if we solve grad(u)=0. Since we don't solve grad(u)=0, and we solve grad(ρu)=0, then the fluid is compressible careless of what the density depends on, pressure or temperature.

I am just trying to understand what Fluent solves for.

Thank you for your reply.


Leverkin March 5, 2009 17:41

Re: Incompressible Ideal gas law
 
I keep doing the same error. It is not grad(ρu)=0. It's div(ρu)=0. Sorry for this mistake but I don't use this notation at all!



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