Behavior at low temperatures

[Zdenour]

Hello,
I remember we talked about this topic a long time ago, but I am not sure what was the conclusion.

I am trying to use Mutation++ to determine thermal and transport properties in our free-stream rebuilding code (based on CABARET) for the Longshot facility. We assume nitrogen in thermal equilibrium everywhere. The static temperature can be as low as 70K.

• The first issue is regarding viscosity, which is now overestimated at such low temperatures, see the attached plot. With the help of George, I have found a workaround for me resulting in a “corrected” curve shown in the plot (basically switching back to "exp-poly" for the pairs of interest in the collisions file). I was wondering if a more systematic solution could be found. See, that in the past, the behavior for low temperatures was just okay.

• The second “issue” is concerning the NASA-9 polynomials. I prefer them over RRHO. However, they are usually limited to about 200K. When extrapolated below this limit, they result in unrealistic data. My workaround was to add a temperature range from 50K to 200K, where data smoothly go from the polynomials to the result of RRHO. Would it be possible just to clamp the values at the lower bound instead of using the polynomials beyond their validity? I believe this would result in more reasonable behavior.

I know that your concern is not at such low temperatures. However, it could help Mutation++ to spread for use in ground test facilities.

As a (dummy) user, I apologize in advance if I missed some options already implemented.

Thanks!

viscosity_Mutation++_NEW.pdf

[jbscoggi]

Hi @Zdenour, sorry for the late reply to this. I will try to look into why the viscosity is so different in the current M++ version. To help me out, can you tell me what mixture you are using, which species pairs you had to "correct" etc.

As for the NASA-9 polynomials, yes I think clamping should be the desired behavior. Are you a programmer and know C++? If so, would you mind trying to work on this update yourself and submitting a pull request? If not, that's OK, it will just take me some time to get around to it.

[VirgileCharton]

Hello,

I am a new user of M++, and I am very interested about the above request as I also work with low temperatures and NASA-9 polynomials. How does M++ handle the temperature below 200K in that case ? Is there a threshold or are the polynomials used beyond the temperature validity range ? Thank you very much.

Regards,

Virgile Charton