I want to keep inlet pressure fixed and outlet pressure equal to atmosphereic pressure. I use inlet pressure and inlet mass flow rate at outlet pressure. I hooked an udf so that I can get atmospheric pressure by adjusting mass flow rate. But when I use mass flow inlet at outlet then face pessure F_P(f,t) and cell pressure C_P(c0,t0) adjacent to face at outlet is equal.Which is not physical. can any body tell what is the problem. All pressures are total pressures. I can use inlet and outlet pressure but in that case solution diverges so want to control the solution by adjusting massflow rate. This is why I am using mass flow inlet at outlet. Thanks in advance. mech

Hi,

I don't think that what you try to do is right. Keep your first inputs with inlet and pressure outlets. Define correctly the operating pressure (define->operating conditions). Be aware that all your inputs in Fluent about the pressure is a gauge pressure and not the total pressure (total pressure=gauge_pressure+operating pressure). Furthermore you must NOT include the hydrostatic pressure in the gauge pressure because Fluent includes it automatically in the body force if it's an incompressible flow (have a look at Fluent manual about pressure outlets and inlets.....)

If the solution still diverges, you should review your scaled residuals, your mesh, discretization schemes.

Fab.

Hi Fabrice Thank you for your good advice. I am simulating 2D micro parallel channel flow. It is laminar but compressible flow. I am using Nitrogen gas. In my case the channel width is 1.2 micron. when I use 12 mesh in normal direction to the flow it is converging. But when I use 23 mesh then it is diverging.This is my problem. So I wanted to fix inlet pressure and to initialize the solution from outlet with outlet pressure and mass flow rate so that I can fix outlet pressure by adjusting mass flow rate so that I can control the divergency. In my case gause pressure=total pressure because I am using operating pressure 0. To do the above I need staggered grid. I do not know how to use staggered grid in fluent. If you have any idea please suggest me. Mech