[Techies]

Hi guys,
I'm trying to simulation the air through the reactangular duct which has 4 cylinder inside. My boundary condition is velocity inlet 9.45(Re=15000), pressure outlet =0, lower wall is heat wall, heat flux is changed from 500 to 5000. But when i changed heat flux, my result Nusselt number on heat wall and cylinder absolutely didn't change. Just temperature change. I don't know why. Please someone help me
The second problem is when heat flux from 1000 to 5000, fluent notify " temperature limited to 1.000000e+00/5.00000e+003 in X cells on zone X" at the both first and second iteration . I searched in forum and they said because of grid. I use ICEM and qualify determinant 2x2x2 is around 0.9-1. y+<1 for using kw SST. Anyone met this problem before can help me understand ?
Thanks all.