I’m having trouble trying to simulate a transonic flow over a swept wing (Mach = 0.85). I’m following the steps of the “Aerospace Workshop feat. EUROAVIA (Session 3) ― Compressible Aerodynamics of an Aircraft”, and the simulations are not converging. I set the inlet velocity as a ramp function, starting in a low speed, and the residuals go chaotic when the solver reaches the timestep programmed to set the velocity to M 0.85. Does anyone have a similar problem? Is there any parameter I should pay special attention to and I’m ignoring? The project link is:
I’m new to SimScale and saw your question on forum and was quite interesting to investigate the problem.
I will try to give some suggestions and let’s see if it works.
The Mach number simulated in the SimScale workshop was 0.35, as I understand would want to increase the Mach number to 0.85 (a very high sub-sonic regime).
Every airfoil has a defined “Critical Mach Number” which is stated as the free stream Mach number for which the sonic/supersonic conditions start appearing on the airfoil, this critical mach number is fixed for each airfoil. Now as soon as the aircraft travels in this critical region, the sonic boom starts appearing on the airfoil and this degrades the performance of the aircraft. I just had a look at Airbus A320’s critical Mach number and literature shows that it is 0.89. [more info on critical mach number for airfoils: http://www.fzt.haw-hamburg.de/pers/Scholz/arbeiten/TextCiornei.pdf]. This clearly means that the flow is tending to sonic (chocked) and supersonic regime.
Now the problem is you want to simulate the conditions at Mach 0.85 with the same initial conditions as 0.35, this might cause problem because of dependency of k and omega values on the Reynolds number. Re (Reynolds) number for Mach 0.35 is 4.4e7 and Re for Mach 0.85 is 1.07e8 (Assuming root chord of 5.5 m).
k and omega values for these conditions will be different, one needs to have deep look at the values to be used for such cases.
Try playing with k and omega values (Preferably lower omega value), and see if it works. In any case, I would be happy to investigate this problem with you.
