HyShot II_Scramjet case can't run

[tai-yichen]

First of all, thank you very much for developing and maintaining hyStrath / hy2Foam.
I am currently simulating the HyShot II scramjet configuration using hy2Foam, and I would like to report an issue I encountered and seek advice from the developers.

The solution remains stable during the initial flow development, numerical instabilities consistently occur after fuel injection and shock formation, leading to non-physical temperature drop (Tv/Tt) and divergence.

Species: O, H, O2, H2, OH, H2O, HO2, N2
Air inlet boundary conditions
Composition: O2 = 0.233、N2 = 0.767
Velocity: fixedValue (1800 m/s)
Temperature: fixedValue (1500 K)
Pressure: fixedValue (57000 Pa)

Fuel inlet boundary conditions
Composition: H2 = 1.0
Velocity: zeroGradient
Translational-rotational temperature (Tt): totalTemperature = 300 K
Vibrational temperature (Tv): zeroGradient
Pressure: totalPressure = 297000 Pa

**wall conditions **
Velocity: noSlip
Translational-rotational temperature (Tt): fixedValue= 300 K
Vibrational temperature (Tv): zeroGradient
Pressure: zeroGradient

Initial conditions (internalField)
Velocity: uniform (0 0 0)
Pressure: uniform 57000 Pa
Temperature: uniform 1500 K

Species vibrational temperature conditions
O、H: Tv = 0 K
O2、H2、OH、H2O、HO2、N2:
Air inlet: fixedValue 1500 K
Fuel inlet: zeroGradient
Internal field: uniform 1500 K

controlDict
startTime 0;
endTime 0.0025;
adjustTimeStep yes;
maxCo 0.1;
maxDeltaT 2e-9;

The numerical instability occurs at t ≈ 2.1e-4 s, with a time step size of approximately Δt ≈ 1.34e-9 s. The computational mesh consists of approximately 5 × 10⁵ cells. The schematic is taken from the following reference: [](https://www.sciencedirect.com/science/article/pii/S1270963824004887)

I would greatly appreciate any suggestions or recommendations on how to improve or modify the setup.
Thank you very much for your time and help.
Environment

• Ubuntu 18.04 LTS
• hyStrath version: latest
• Solver name: hy2Foam

[timeExplore]

I am unfamiliar with supersonic reactive flow under thermal non-equilibrium assumption. But I think you could try to review your fuel inlet bc condition as U can be set as pressureInletOutletVelocity. And original totalTemperature may not work. You can refer another post:“[Total temperature boundary cannot be set in the Tt file when using hy2foam (https://github.com//issues/166)”

[tai-yichen]

Thank you very much for your reply, it was very helpful.

I tried applying a temperature bound and setting Tlow = 200 K, and this seems to resolve the issue for now. However, I am not fully sure whether this should be considered a physically/ numerically proper solution, or just a temporary workaround.

I will continue investigating this, but I really appreciate your input and guidance.