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Issue using the air-5species Park model in Hypersonic Flow

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Old   May 7, 2022, 03:40
Default Issue using the air-5species Park model in Hypersonic Flow
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Hello everybody, hope you are all doing well.
I am having troubles with solving the following hypersonic flow problem in Fluent:
I have a 45 degrees, Mach 21.4, inlet pressure 9.79 [Pa] flow coming from the left side and hitting a blunt body (the mesh is the one in figure with a zoom near the stagnation point) before leaving the field through the outlet on the right side. The body is the nose of a re-entry space vehicle. I am studying both the 2d and the 3d problem but I get into the same trouble regarding ricombination of N2. Let's start from the 2d case. The used settings are the following:
-2d, planar, steady, density based
-Models: Energy ON with 2-temp model activated, laminar flow, radiation on the wall, Species (with reactions) using the air-5species Park model
-Materials: Mixture of air with 5 species (automatically inserted by Fluent)
-Cell zone condition: 0 operating pressure
-Inlet BC: Pressure Far Field with p=9.79 Pa, M=21.4, 45°angle, 226K for the T, 0.233 mass fraction for the O2 (the others are 0 anche N2 is automatically calculated)
-Outlet BC: Pressure outlet with 9.79 Pa, 45° angle and same mass fractions (I also tried different combinations)
-Wall BC: Adiabatic with 0 heat flux and radiation towards the flow with epsilon=0.8, zero diffusive flux for the species
-Method: Implicit AUSM, Green Gauss Node Based, I did both First Order and Second Order
-Initialization from inlet with also a FMG initialization

My only (but big) problem is the fact that the Nitrogen starts recombinating in the boundary layer and so I obtain again 0.72 mass fraction for N2 on the wall. This is totally unexpected and makes me have high Temperatures on the wall (about 1800K) and as a consequence a really high radiation heat flux (about 450 kW/m^2, the radiative equilibrium is satisfied). I have experimental data (that unfortunately I cannot share) in which there is no recombination in the boundary layer so there is no creation of energy (due to the recomb. process) and so the temperature are far below (about 1400K) with a radiative heat flux of about 200 kW/m^2. I am also adding pictures regarding the species so that the situation is more clear. Thank you for your time and your patience, every suggestion is well accepted. If you need any other picture let me know.
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catalytic, hypersonic, recombination, species, two-temperature model

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