reversed flow over thin plate

qiaomei

dear fluent experts,

pls help! i'm modelling 4.5m/s air flow over a thin plate. after setting 0.01 for all residuals and iterating for 2000 iterations, all results diverge and i had reversed flow in outlet from the 1st to the last iterations.

the following are the parameters i used in fluent:

->Solver: pressure-based solver, implicit formulation, steady time, 3D space, absolute velocity formulation, green-gauss cell based gradient option, superficial velocity porous formulation

->viscous model: spalart-allmaras (1 eqn), vorticity-based production, default model constants

->solution controls: using flow & modified turbulent viscosity equations, simple pressure-velocity coupling, default under-relaxation factors, and standard pressure, first order upwind momentum & modified turbulent viscosity discretization

i would really appreciate if someone can tell me where did i go wrong and if any additional information is required.

thank you so much!