If you are using a Fluent version higher than 12, you should make use of the rotation and curvature corrections implemented for both the S-A model and the SST model.

Agood method for stabilizing the solver you might try to start with a lower courant number, (perhaps at first you could try to not use the energy equation - although at higher than 0.3 Mach you should eventually use it). 

If you can provide a bit more details on the case you are running maybe we could troobleshoot it more efficiently.

I am investigating the benefits of circulation control on a supercritical aerofoil. All my simulations run at Mach 0.1 but the jet at the trailing edge can reach up to Mach 0.3-0.4.

I initially tried to run the simulations with a wall spacing y+ of around 15-35 but I soon realised that I need to decrease that value to about 1 to accurately model the viscous sublayer and get better results at higher angles of attack up to stall.

The issue I am facing at the moment is that my solution doesn't converge but oscilates as you can see in the two pictures attached.

I tried to increase the number of elements in the chordwise direction but then the simulation oscilates even more so I don't really know how to solve this.

I think that the problem  may be physical not numerical, i.e. if your airfoil approaches stall, the flow structure may become unsteady - I have seen this with NLF airfoils aswell (although not with super circulation). If you are using entrainment effects at the trailing edge, the aparent aerodynamic angle of attack may become significantly greater than the geometric AoA - hence the airfoil might enter its stall earlier than you would expect. 

In your case I think that it may be a good idea to consider URANS or even LES if you want to go deeper into stall control. Otherwise the solution looks converged by me (you will rarely see a straight flat line). However I think that there may be something odd with your reference values because the CL looks a bit low for a high AoA supercritical airfoil.

I hope this helps

This simulation is actually at 0 AoA so the aerofoil is not stalled yet. I got straight lines before when I used values of y+ which were larger and the boundary layer was computed using the wall functions.

Hello , 

I started simulating flow across Naca 0012 , and i got a very accurate data comparing to other studies . I faced A crash at my first simulations , U may need to Check if Your trailing edge of the airfoil is properly closed and the Mesh is Closing around all the walls of the air foil, Unless it will Crash and will not Converge. 

Hope i Helped 

Regards 

A couple of questions;

Do you get straight line convergence without jet application?

Is it a constant blowing jet?

The case you described was run in a time-accurate mode?

I don't really know how exactly the jet is being applied, but being close to the TE even small fluctuations due to the jet interaction with the surrounding flow might have an effect on total lift through the Kutta condition.

Arvin, at the moment I'm running steady state RANS with a constant tangential blown jet. Today I actually tried to use an extra velocity monitor just off the trailing edge and got a convergence on that.