Learning Forum

[manu prabha anand]

I had given mass flow inlet, out flow outlet boundary condition, but i get an error in pressure calculation, i had given inlet pressure as 101325Pa, and operating condition as 0Pa, I am attaching the figures and boundary condition. does any bodyhave a clue about where i am wrong?

[Rob]

Why are you using an outflow boundary? What is the material density?  

[manu prabha anand]

Material is air, Out flow is used because i do not have an idea about the pressure at the exit. My question is in coupled solver how the pressure is calculated when mass flow is given at inlet or velocity inlet boundary is specified ? . Do you think pressure outlet will correct the result? Is it necessary to specify inlet supersonic gauge pressure? Then how to caculate the pressure if i give operating pressure 0Pa. 

[manu prabha anand]

I have another doubt, if i use pressure outlet at exit and specify the exit pressure at the outlet to 0Pa, the how the pressure at exit is calculated? Is the pressure is fixed? or like in outflow the pressure at boundary is calculated using the precalculated values from upstream cells? What is the difference in fluent Enterprise, premium, pro? Is there any difference in solver algorithms? I am using Fluent enterprise.  

[manu prabha anand]

I have checked SIMPLE solver also , I am getting same results.

 

[Rob]

Operating density is effectively the atmospheric condition, we then set the solver pressures as gauge against that. The Outflow boundary is ancient, and if you read up on it, was never designed to work with compressible flows. 

Have a look at some of the tutorials, click on Help in Fluent to access. Also, review the CFD courses under Learning (book icon left side of the screen on this page).