How to modify gas constant or special heat ratio in CFX-Pre?
 

I must modify gas constant or specific heat ratio in CFX-Pre.
Because I investigate the effect of fuild property, such as operating characteristics when the gas constant is constant and specific heat ratio is different.
Thanks

If you modify molar mass M, you also modify specific gas constant r (r=R/M), so you modify also heat ratio Cp/Cv. See Mayer's relation for gas (Cp = Cv + r).

Could I modify directly gas constant or specific heat ratio in CFX-Pre?
 

Could I modify directly gas constant or specific heat ratio in CFX-Pre?

You cannot modify the specific heat ratio, nor the gas constant directly in CFX-Pre.

May I ask what is your goal changing the gas constant, and/or the specific heat ratio? It seems you are making an assumption those quantities are used inside the software somehow. From what I understand, they are not used anywhere explicitly.

You can rewrite the fundamentals in reverse

R_gas = R_universal / Molar Mass ---> Molar Mass = R_universal / R_gas which you can change at will

Cp - Cv = R_gas
Cv = Cp / SpecificRatio --> Cp = SpecificRatio * R_gas / (SpecificRatio - 1)

Hope the above helps,