Learning Forum

[ghostrider034]

Trying to validate the DLR geometry of scramjet using fluent. In this, hydrogen is injected into the supersonic air stream.

Boundary Conditions:

Air Inlet – Pressure Inlet – Mach No. 2

Fuel (Hydrogen) Inlet – Pressure Inlet – Mach No. 1

Air Outlet – Pressure Outlet

At walls – No-slip boundary conditions

Turbulent Model – SST k-ω

Tried the above problem on 2 versions of fluent (version 17.2 and version 21R1) using Density-Based Solver (implicit)

On version, 17.2 solution is converging for cold flow (only mixing no combustion)

But in version 21R1 solution is not converging . Are there some major changes in density-based solver in these two versions??

[Rahul Kumar]

Hello,
There are some changes in the code between versions 17 and 21R1. There could be multiple reasons for it not converging in 21R1. Please try the following :
Check the mesh, make sure min orthogonal quality is greater than 0.1
In materials, I hope you are using ideal gas for density. Also, make sure operating conditions is set to zero.
Try using Green Gauss node based with AUSM.
Reduce the courant number (start with around 0.5 and you can increase it gradually in the course of the simulation).
If there are sharp discontinuities in the flowfield, consider using a mesh adaptation using a variable.

[ghostrider034]

I have implemented all the 5 points you have mentioned but still, my solutions are not converging. I am doing steady-state 2D simulation.
Errors I got while simulating:-
Reversed flow on 4 faces (8.2% area) of pressure-inlet 17
Absolute pressure limited to 1.000000e+00 in 47 cells on zone 10
Temperature limited to 1.000000e+00 in 2 cells on zone 10
Temperature limited to 5.000000e+03 in 84 cells on zone 10

[Rahul Kumar]

Can you please post a few monitor plots, pressure/density/ Mach No contours?