Turbulence model / Boundary layers on a cylinder (VIV with 2DOF)
 

I hope someone can help me on this one.

I am modelling flow across a cylinder with Re=50000. As the flow is subcritical and has laminar boundary layers on the cylinder (Re< 1 x 10^5), can I model this flow using a turbulent solver? I'm not interested in the flow field, just how forces acting on the cylinder. I am producing simulations of VIV on a cylinder with 2DOF.
Or do I have to use a turbulent model to solve this case?

Thanks,

P

...
 

Are you sure, that your flow is subcritical? Re(critical) is about 10000 = 10^4 for cylindric pipe.
Without any turbulent model (or DNS, or LES) you couldn't resolve turbulent vortices right in boundary layer.
I think, you should use turbulence model.

Ill look into what Re the boundary layers separate. It is flow over a circular cylinder (external flow).

I have been doing a bit of reading and a few people recommend using the K Omega SST turbulence model. To use this model effectively I have read that the Y+ value should equal ~1. The mesh required for Y+ ~1 are big, and will take a long time to solve.

I have played about with various solvers (turbulent ones) and cant seem to get vortices to form. I have been using flow with the following characteristics -

Density = 1025 Kg/m3
Viscosity = 0.001008
Cylinder diameter = 0.5 m
Flow rate = 0.1 m/s

Re = 50843.254

Any advice on how I can get vortices forming?

Many thanks for that reply.

turbulence...
 

And how do you understand, that no vortices are forming?
Do you look vectors or pathlines? Or k,e and turbulent intencity?
I had same question too, but didn't found answer in www. In my opinion, our nodal grid for some cases are much bigger (0,09 mm versus 10^-4) than turbulent length scales (macroscales). Higher the turbulence, bigger these scales - in my flow they rose to 0,7 mm. It continues to some limit, than these scales appears to decrease...
That's only my own conclusions and calculations, any specialist's agreement/critics is needed. ;)
:)
You wrote, that fine mesh (y+ about 1) is not a variant. Do you use y+>30 with standard wall function? Make sure that.