A stable unstable flow?

Jonathan Vogt

I'm having a curious problem: I'm running an unsteady 2d case with an inverted wing in ground effect which, although clearly seems to be shedding vortices at the rear, the lift and drag plots are very stable (only changing in the fourth or fifth decimal place) as if the flow were stable. the plots don't seemt to change appreciably which, as it looks unsteady, is disconcerting.

I'm running with a moving ground plane and using using Reynold's Stress turbulence model. I'm using time steps of 0.001 sec and 20 iterations per time step. Could it be that I'm not letting it run long enough during each time step to obtain a different value because, theoretically, lift and drag should be fluctuating but they're very steady.

Thanks for your help. Jono Vogt.