# Need help to setup supersonic flow simulation of a ramjet

Hello everyone!

I’ve been trying to simulate the flow inside and outside of a ramjet recently. The flow speed must be Mach 1.4, or 480m/s, at 100000pa. I’ve been having troubles obtaining results which made sense, and so decided to create a new project and ask for help here.
How should I set up the boundary conditions for this? Would a velocity inlet and a pressure outlet work fine?
I’ve tried doing this in the past, and got results which made no sense, such as negative temperatures (in kelvin) and pressures of -5e8 pa inside the inlet (which is supposed to compress air).

Below is a link to my current project, which I hope someone here can give advice on how to setup:
https://www.simscale.com/projects/cdhenin/p15_ramjet_cfd/

Best

Charles

Hi Charles and nice project you got here!

I am tagging @Get_Barried here as we discussed some compressible flow cases in the past - so he can add his two cents here. Regarding your project I would not perform this as an external flow analysis but rather an internal one with the ramjet “closed” in the sense that we add a face at the inlet for the velocity inlet and a face at the outlet for the mentioned pressure outlet, that should work. We can also simplify the case by going from 3D to 1D, Barry has also worked with Darren (@1318980) on these kind of simplifications which will save you a lot of computational power.

Cheers,

Jousef

Hi @cdhenin,

Jousef has pointed out correctly and critically that a full 3D analysis is much much too computationally expensive to run. We’re talking about run times of easily a week provided we overcome all the hurdles that come with simulation of compressible supersonic flow. The mesh itself would already take you weeks to optimize and fix.

So, do start with a completely simplified model and in 1D as jousef has mentioned along with the internal being considered only first. Flow outside of the ramjet can be done later.

Start with making the needed 2D geometry first and we will work from there.

Cheers.

Regards,
Barry