[shiva krishna]

Hello everyone,
I am working on a simple rectangular geometry with air as fluid .one side of rectangular face is an inlet and other side of rectangular face as outlet and reaming faces will be walls ,so i want atmospheric conditions at both inlet and outlet, for that i have taken pressure inlet and pressure outlet with default values (i.e. Gauge pressure is Zero).

But unfortunately when I am simulating I am getting reverse flow. Moreover my solution is converged. and i am using K-epsilon method to solve my problem. Could you please any one explain me. What kind of mistake I have done. I am attaching my simulation Residual and mesh images. Thanking you in advance.

For your understanding i am attaching my procedure.

1. Sweep mesh and inflations layers at walls
2. Pressure based solver
3. Material-Fluid-Air-Default value (i.e. air with density 1.225)
4. K-epsilon (Standard) equation
5. Inlet-pressure inlet-Default values
As i said i want atmospheric conditions at inlet as well as at outlet, for that I have taken pressure inlet and pressure outlet with default values (i.e. Gauge pressure=0) more over specification method values also default (i.e. Intensity and viscosity Ratio).moreover I have tried with using Intensity and Hydraulic diameter with this formula (2ab/a+b) at inlet and outlet. But I am getting same kind of results.
6.outlet-pressure outlet-Default values( i want atmospheric condition)
7.solution method
7.1 SIMPLE
7.2 Least squares cell Based
7.3 pressure- Standard
7.4 I kept reaming all are First order upwind
after converging I have changed these method are into second order upwind
8.Hybrid Initialization

[zhihuawan]

Originally Posted by shiva krishna

Hello everyone,
I am working on a simple rectangular geometry with air as fluid .one side of rectangular face is an inlet and other side of rectangular face as outlet and reaming faces will be walls ,so i want atmospheric conditions at both inlet and outlet, for that i have taken pressure inlet and pressure outlet with default values (i.e. Gauge pressure is Zero).

But unfortunately when I am simulating I am getting reverse flow. Moreover my solution is converged. and i am using K-epsilon method to solve my problem. Could you please any one explain me. What kind of mistake I have done. I am attaching my simulation Residual and mesh images. Thanking you in advance.

For your understanding i am attaching my procedure.

1. Sweep mesh and inflations layers at walls
2. Pressure based solver
3. Material-Fluid-Air-Default value (i.e. air with density 1.225)
4. K-epsilon (Standard) equation
5. Inlet-pressure inlet-Default values
As i said i want atmospheric conditions at inlet as well as at outlet, for that I have taken pressure inlet and pressure outlet with default values (i.e. Gauge pressure=0) more over specification method values also default (i.e. Intensity and viscosity Ratio).moreover I have tried with using Intensity and Hydraulic diameter with this formula (2ab/a+b) at inlet and outlet. But I am getting same kind of results.
6.outlet-pressure outlet-Default values( i want atmospheric condition)
7.solution method
7.1 SIMPLE
7.2 Least squares cell Based
7.3 pressure- Standard
7.4 I kept reaming all are First order upwind
after converging I have changed these method are into second order upwind
8.Hybrid Initialization

I see that the mesh you are using is not the perfect,can you check the mesh quality?

[CFD-fellow]

Flow needs pressure gradient. So if both inlet and outlet is going to be atmospheric how do you expect to have flow?
By the way reversed flow is because of higher pressure in the outlet. The reason is the difference between pressure inlet and pressure outlet definition. Pressure inlet is total pressure and pressure outlet is static pressure. So if you set the both values the same then the outlet static pressure would be higher than inlet one and reversed flow is the result.

[hitzhwan]

Originally Posted by CFD-fellow

Flow needs pressure gradient. So if both inlet and outlet is going to be atmospheric how do you expect to have flow?
By the way reversed flow is because of higher pressure in the outlet. The reason is the difference between pressure inlet and pressure outlet definition. Pressure inlet is total pressure and pressure outlet is static pressure. So if you set the both values the same then the outlet static pressure would be higher than inlet one and reversed flow is the result.

it has velocity from inlet,it can flow into the channel.

[CFD-fellow]

Originally Posted by hitzhwan

it has velocity from inlet,it can flow into the channel.

Both boundaries are pressure ones, as it is mentioned in her procedure. There is no velocity inlet boundary condition in her simulation I think.