[alubacyj]

Hello everyone，
First thank you for answering my question.Now I am simulating an impingement jet case in cfx14.5，and there is a really big range of the airflow temperauture（298K~700K）between the pipe outlet and the target heated wall.So I need adpot the real air gas properties rather than constant.But I don't know which materical to choose. I have searched on the forum and some one said the mixture of idea oxygen and idea nitrogen can be used；And another one thought the properties can be a variable of temperature， just replace the properties such as density by polyomial.If you know some polypmial please tell me.
So which way is better to choose or there is some material I can choose directly？
Thank you for your time.

[alubacyj]

Eeeeeee, can some one tell me which material can I choose?Because I think the real air is really common in cfx, I think there should be some material I can select directly

[urosgrivc]

Why dont you just use >Air ideal gas< in cfx, it has a constatnt Cp.

[alubacyj]

Because of the wide range of the air temperature， the viscosity and thermal conductivity is not constant（actually it varies with the temperature). But in air ideal gas model, those physical properties are constant.

[urosgrivc]

You are able to make tempearture dependant properties by:

Creating a User function importing temperature dependant variables in a table form.
Than make an expression=> userfunction(T) < -(T) stands for temperature dependant be carfull as (t) stands for time dependant it would warn you anyway becouse of diferent units,
Than insert expression as a materal properti

Now cfx will look in the first column(temperature) and output your desired (variable) column 2 of the table input

But Heat capacity is also density,pressure dependant.
And I dont know how this will effect the solution
As i only use this in solids not fluids where there is a lot les variables no(pressure, density, viscosity) change .

[alubacyj]

Thank you very much for your reply.
So I plan to use air idea gas, so the density will change with the temperature and pressure.Then as you told me create User functions for the thermal properties.
So am I right by doing things above?

[urosgrivc]

Density will avtomaticly change with temperature and pressure as Air ideal gas folows the ideal gas law.
Densiti will be calculated and will not be a constant if you change to air ideal gas.

As this will now be density based solver as I understand.
not a pressure based solver where density is constant.
And i dont see a problem by seting temperature dependant thermal properties. You could even make them temperature and density dependant.

I would like an aproval of this by some expert here on the forum please.

[ghorrocks]

As this will now be density based solver as I understand.
not a pressure based solver where density is constant.

No, this is not correct. CFX is always using a pressure based approach. It does not have a density based solver option. It just uses a pressure based approach with variable density for compressible flows.