# How can you do Supersonic Simulations of aircraft?

#1

Hi Community!

I am a high school student that wants to use CFD for a science fair project. I am also an aspiring aerospace engineer but very new to computational fluid dynamics. For my science fair project, I have a few aircraft design ideas that will reduce the angle of a shock wave. I want to use CFD to observe or measure this effect.

That being said, do you know how I can use SimScale to model airflow around an aircraft. I’ve played with the system but I am not sure how to do speeds above Mach 1. Is it even possible to supersonic simulations with SimScale? If so, would you be willing to give a relatively rudimentary tutorial? Additionally, how can I use CFD to visualize the formation of a shockwave? Are there any measurement outputs that will help me to observe or approximate the sound levels from different distances from the aircraft?

Thanks!

#2

Hi @rtemp!

Supersonic simulations are possible but are very tricky to master as they easily diverge. A model you might be interested in from my colleague Ali can be found here: https://www.simscale.com/projects/Ali_Arafat/compressible_aerodynamics_of_commercial_aircraft/ - maybe also @Get_Barried can comment if he has more to add as he is probably the one with the most compressible runs here

Cheers,

Jousef

#3

Hi @rtemp,

Well let me start by saying supersonic flow is not exactly simple because for supersonic flow, rhocentralfoam is used and this is a density based transient solver. This means it will be very very expensive to run something as complex as a full aircraft or in this case, 3D dimensional object unless you have a very consistent and relatively coarse mesh.

So if you’re new to CFD, I would say this project may be a little bit too much. However, I do have a suggestion but it is also not so easy.

Instead of an entire aircraft, you could look into supersonic wing cross sections and simulate that in 2D. Once you get the default geometry running, you can modify the features of that cross section and observe what happens to the performance during supersonic flight condition.

This is nearly identical to the shock diamond simulation that I have somewhat completed which you can find here. Your main difficulties are as follows:

• Selecting a supersonic wing profile
• Creating a 2D wing profile in CAD
• Get a consistent but quite coarse mesh for that profile (in Ansys mesher or here in Simscale which is much much harder to control)
• Translating that mesh into a 2D Mesh
• Justifying and setting up your boundary conditions (Mach no selection etc)
• Data result extraction (CL? CD? Pressure? Normalization of velocity to mach for visualization? all in ParaView as well)

So do evaluate these pointers and the amount of time/effort you want to put in.

Of course, I would be more than happy to guide you along, but it is as mentioned, a lot of work.

Cheers.

Regards,
Barry

#4

Thanks for the information, @Get_Barried

I am restricted on time, so I guess I’ll have to drop this project for now. That being said, I would still like to learn CFD, especially with supersonic flows. Are there any resources you can direct me to? I looked at your shock diamond simulation project, and I am not sure how to replicate it.

Thanks!

#5

Hi @rtemp,

Well if you want to learn CFD, supersonic flow is definitely not the best place to start .

In supersonic flow, air cannot be assumed as incompressible. This inherently brings in much more complexity in terms of the general equations used to describe flow behavior at these speeds . Stick to the incompressible flow first.

Since you’re in high school, its a good chance to start early and learn something like CFD if you have the passion for it. A good place to start in terms of reading material is “Computational Fluid Dynamics: An Introduction” John D. Anderson. Even now I still often refer back to that to brush up on some underlying theory.

If you’re looking to learn real quick, a simple incompressible project like verifying the values on some simple/typical case is a great way to start. You get to experience first hand all the quirks and workflow that comes with doing CFD. Better yet, you can do it here on SimScale and ask around if you do run into issues.

It can be overwhelming, the math and the typical issues that usually come with CFD, but won’t know till you try and don’t let anyone discourage you from going ahead.

Cheers.

Regards,
Barry