SimScale CAE Forum

CFD Compressible Flow - Rocket


#1

Hello,

I am fairly new to Simscale but I have chosen to use this platform in order to simulate a steady state compressible air flow around a rocket at a given altitude at maximum speed (5814 ft at 588 m/s). However, I have been trying to simulate this project for a few weeks now with no luck. I am not sure what I am doing wrong, and I would highly appreciate if someone with more knowledge could help me out.

  1. Link to project - https://www.simscale.com/workbench/?pid=4920662020402178442&mi=run%3A133%2Csimulation%3A118&mt=SIMULATION_RUN

    • I apologize I have a couple of geometries open in this one project. I am looking at the “airbrakes-90 degrees” geometry specifically with the “Air Brakes- 90 degrees” simulation!
  2. The mesh is complete, and I believe it’s sufficient for the most part. However, I do keep getting the error of 'maximum number of iterations exceeded". I tried manipulating the simulation controls and making sure that my boundary conditions are suitable for what I am testing. Essentially I would like to compute the drag and lift coefficients as well as the forces on the body of the rocket. I did take a different path in modelling the rocket itself, as I modelled the fluid domain as a part.

  3. I am trying to simulate a compressible air flow around the rocket. I obtained the maximum velocity value from OpenRocket (a rocket simulator) as well as the pressure value of the air and calculated the density and dynamic viscosity through separate calculations.

If anyone could help me out I would greatly appreciate it!


#2

Hi @mben_aoun and nice approach!

@Get_Barried has carried out some comp. simulations in the past and they are quite…stubborn I’d say. Could you have a look at the user’s setup please Barry and give him some tips?

Will jump in shortly. Also interesting for me as I have to catch up with my Falcon Heavy sim at some point… :thinking::sunglasses:

Best,

Jousef


#3

Hi @jousefm,

Thank you for taking the time to look at my question! Looking forward to hearing back from you and @Get_Barried!


#4

Hi @mben_aoun,

Sorry for the really delayed reply! Absolutely swamped with work this week despite the on-going global situation :stuck_out_tongue:

Compressible steady-state simulations are notoriously tricky so this may be a little difficult to solve. But would like to know some information, what is your flow speed in Mach?

As for the boundary conditions, I believe the 90 degree faces should have the Symmetry BC instead of pressure outlet. Pressure outlet 3 is correct though.

I believe the major source of error lies in using a steady-state compressible simulation, need to know your mach no first so let me know.

Cheers.

Regards,
Barry


#5

No problem!!
The mach number I’m running this simulation at is 1.7!


#6

Hi @mben_aoun,

Cool, that would mean steady-state compressible simulations are indeed not workable here. You will need to transition out to pressure based transient solvers. Simply set the solver to transient.

Before that however, have you tried to adjust the boundary conditions as I have described earlier?


#7

Great, I’ll run a transient simulation with the symmetry boundary conditions and let you know how it goes! Thank you for your help :slight_smile:


#8

Hi @mben_aoun,

Please note transient simulations are very computationally expensive. You will need to optimize your mesh and run time. Suggest starting with a small end time and keep in mind the courant number has to be less than 1. You want to see if the flow is reacting first before going for a full run.