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Calorically Imperfect (Hypersonic) Gas in Fluent?

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Old   April 8, 2016, 17:27
Default Calorically Imperfect (Hypersonic) Gas in Fluent?
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Dan
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Does Ansys Fluent have the capability to model Calorically Imperfect Gas? I've been trying to accurately model gamma for high temperature air with no success. https://www.grc.nasa.gov/www/BGH/realspec.html

I have a test article being impinged by a flow with the following free stream conditions:
T ~ 5500K
P ~ 9 bar
M ~ 3.3
I've determined the mass fraction for each species from NASA CEA and entered them as a boundary condition.

First I tried using the material properties from the Fluent Hypersonic re-entry pod example. I kept getting a gamma of ~ 1.36 in the free stream. This is causing my total temperature, and shock pressures, temperatures and stagnation heat flux to be off. I tried creating a new air model with 5 species (Park) reactions, and Cp for each species from NASA CEA. Same solution.

I've checked the mass fraction of each species in the free stream and it matches my boundary condition input. The static temperature and mach number also match. Total temperature is significantly off, due to gamma being off. The specific heat of the gas in the free stream matches the "frozen" value from CEA. I've verified the mixture Cp in the free stream is the mass weighted average of Cps of all the species in the free stream at a local static temperature. I've verified the local mixture gas constant is also a mass weighted average. It appears that Fluent is calculating gamma based on an equation for constant specific heats (gamma = Cp/(Cp-R)). Is this equation valid for dissociated air? If not, is there a setting to have Fluent calculate it with the correct equation. Also, is there a way to get Fluent to display the equilibrium (rather than frozen) value for mixture heat capacity? Currently the flow is being modeled as an ideal gas.
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