Expert Parameter for compressible transient

ioannis

Hello,

I am simulating the compression stroke of an internal combustion engine and I have problems when setting the expert parameter "pref for compressible transient" to true.

The working fluid is air ideal gas and then I plan to inject ch4, in order to see how the mixture homogeneity evolves with the piston motion.

The solver gave me the notice that I should set the expert parameter: "pref for compressible transient" to true. I set this parameter to true and then came another error:

+--------------------------------------------------------------------+ | Reference Pressure Information | +--------------------------------------------------------------------+

Domain Group: Cyl

Pressure has not been set at any boundary conditions.

The pressure will be set to 0.00000E+00 at the following location:

Domain : Cyl

Node : 1 (equation 1)

Coordinates : ( 2.56243E-02,-1.44915E-02, 1.99480E-02).

I have already had a complete run with the default value of the expert parameter: "pref for compressible transient" set to false. Does this have a big influence on my results? What does this parameter actually do?

I have read in a previous post that for Tascflow one should set the LCHECKP to false, but this doesnt work for CFX5.7.1.

Any suggestions on getting it to work?

Has anybody worked with this problem before? Any tips for doing such a transient simulation? Are there any best practices? Timestepping? Grid generation?Yplus?

I was just wondering if I could see any difference in the results by using a unstructured grid with tetras.

Thank you very much, Ioannis