After writing that the problem was solved by increasing the resolution I realised that I was wrong. I had mistakenly left the option "SmoothAdvection" on, which damped the oscillations but crashed inadvertently after some time. Reducing the timestep does not solve the issue, and I am not sure of what the smoothadvection option does all in all. So my two next natural steps would be:

1) What does "SmoothAdvection" do? Is there any article where this is explained? Is there any some know circumstances under which it may destabilise a simulation? I have realised that the computation seems to crash when the first strong vortices reach the domain exit. Could the boundary conditions there (I use houtflow) somehow destabilise the computation?

2) You mentioned in your email that curved elements that are not sufficiently smooth can be troublesome. I am using gmsh to generate the geometry and the mesh. I have been using splines for the geometry and the high order mesh option to implement curved edges (polynomial on equispaced points) on the airfoil surface. Are there any known issues with curved edges produced with gmsh? When I visualise solutions on paraview, the interelement points seem to follow a smooth curved edge, but I don't know how smooth the edges are in reality.

Many thanks in advance, and sorry for coming back with the same problem.

Cheers

On 05/10/16 18:49, Sherwin, Spencer J wrote:

Hi Fer,

Probably Douglas might be able to comment on this type of simulation since he has just been completing some runs as part of his PhD which has now been examined and accepted. 

I attach a copy of a paper under review which has airfoil situations at Re=1000 at this type of aoa.

My only other comment is that we have seen pressure oscillations when the surface is not curved but I note from your .xml file you do have curved elements. I have not checked how smooth the curved elements you are using. Are there any issues on this side. 

Finally it is possible to specify an inf-sup compatible space for the velocity correction scheme. Definitely using a Modified Expansion and possibly/probably for the Lagrange basis. However the velocity and pressure quadrature spaces have to be the same. The way to specify such a basis is using an Expansion definition along the lines of:

       <E COMPOSITE=“C[0]” BASISTYPE=“Modified_A,Modified_A" NUMMODES="3,3" POINTSTYPE="GaussLobattoLegendre,GaussLobattoLegendre" NUMPOINTS="6,6"  FIELDS="p" />

       <E COMPOSITE=“C[0]” BASISTYPE="Modified_A,Modified_A" NUMMODES="5,5" POINTSTYPE="GaussLobattoLegendre,GaussLobattoLegendre" NUMPOINTS="6,6"  FIELDS="u,v" />

Cheers,

Spencer.