Problem with transient solution of flow past a row of cylinders
 

I am trying to run a 3D unsteady RANS simultation of flow past a row of cylinders in cross flow. To model the row of cylinders, I am using a periodic boundary condition placed at half the cylinder spacing on both sides of the cylinder.

I'm using FLUENT, a structured mesh, and SST k-w viscous model. My spatial discretizations are all first order (to obtain an initial solution) and my discretization in time is second order implicit.

When I run the simulation to enough time steps for the mean flow to cross the domain several times, I am not seeing any vortex shedding downstream of the cylinder. I checked the cell courant number and all are below 1, so I think I have the right time step. And, since there is no vortex shedding, the lift coefficient on the cylinder is zero rather than oscillating at the correct Strouhal frequency.

Any help is greatly appreciated.

-Jason