How to tackle reverse flow. what is the reason for reverse flow. my outlet boundart condition is already set to pressure out (1 atm) this is concerned with gas solid two phase flow simulation

change your geometry or may be consider another boundary condition.

Sham.

Sham

thanks for ur interest . But unfortunately i cant cahnge the geometry or the boundary condition. i want to simualate teh flow behavior that specified condition so what else can i do with

Having reverse flow at a pressure outlet is not necessarily bad. All that happens is that a pressure outlet becomes a pressure inlet, by using the 'reverse' quantities that you specified. Vice versa if reverse flow is recorded at a pressure inlet. So it is important to set sensible numbers for the reverse quantities (eg for the turbulence quantities, chose intensity and length scale)

Sham.

From what I've read, this is the benefit of the pressure-outlet BC. If you used outflow for example, you would not pick up reverse flow and your accuracy would suffer as a result. I agree with Sham.

Your domain size may not sufficient.Extend you domain at outlet and apply Wall-Slip-boundary condition on extended portion.