[yidiragawa]

Hi everyone.
I've to simulate the fan of the CF680-A3 turbofan at an altitude of 35000ft (cruise regime).
The question is about the fluid to take into consideration, will it be Air ideal gas or Air at the corresponding conditions of pressure, temperature, viscosity ...etc ???!
Thank you.

[Abou ali]

In CFD practice, fans are simulated by using incompressible gas so you can use air with constant proprieties at the corresponding altitude.

[ghorrocks]

I totally disagree. If this question is about an aircraft engine at cruising speed the compressibility effects will be significant and so will need compressible flow. I have no idea what CFD practice you are referring to.

Constant properties (of an ideal gas) will be OK for general work, but if you are looking for high accuracy you may well need to consider variable properties for viscosity, specific heat etc.

[yidiragawa]

the fluid must be compressible, since I have to simulate a TRANSONIC fan (in ANSYS CFX 15.0) , at a height(altitude) of 35000 ft

[ghorrocks]

The simplest compressible model is ideal gas. If you add variable properties to that (viscosity, specific heat) it does not add much to run time and makes it a little more accurate. The next step in complexity is a real gas model and that is much more accurate and much more difficult to successfully simulate. But start with the simple ideal gas model and only if you show that it is inadequate should you consider the more complex models.

[yidiragawa]

thank you very much ghorrocks for you thorough replies !