[ARUN K RAJ]

My analysis is regarding flow btw two parallel plates held at constant temperature. I indeed got favuorable results in absence of "g" using inlet velocity (0/U1) and a outlet pressure(0/p). Bt when i add "g" the problem of reverse flow happens within the entire domain i.e, reciruclates happens at mid regions, outlet and sometimes at inlet even. I have noticed that if i fix any value as outlet pressure for a fixed inlet velocity the pressure frm the inlet to outlet starts decreasing (becomes negative) with respect to a fixedvalue uniform 0 assigned at outlet condition for pressure.
The boundary fields assigned are:

0/U1
internalField uniform (0 -0.004 0);
boundaryFields

inlet -- fixed value, uniform (0 -0.004 0);
outlet -- zeroGradient;


0/p
internalField uniform 0;
boundaryFields

inlet -- zeroGradient;
outlet -- fixedValue, uniform 0;

When i put "g" as zero the above conditions works. i get positive pressure from inlet to fixed value 0 till outlet. bt when i put "g" as -9.81 the pressure decreases in the domain and that causes reverse flow. is there any suitable boundary conditions to figure this out. ( for me i need the value of velocity as -0.004 at inlet, so any suitable suggestions for the same)?