CFD Online Discussion Forums

CFD Online Discussion Forums (
-   FLUENT (
-   -   velocity inlet and pressure outlet (

Ebrahim April 10, 2008 11:51

velocity inlet and pressure outlet

I'm simulating a flow with a 'velocity inlet' and a 'pressure outlet'

my velocity is 25 m/s at the inlet. but i have to set turb kinetic energy and turb dissip rate in my boundary conditions.

how do i calculate these variables?

same question for the pressure outlet. there i have to calculate 'backflow turb kin energy' and 'backflow turb dissip rate'

thx a lot!

red lemon April 11, 2008 03:30

Re: velocity inlet and pressure outlet
you need to know what the turbulence conditions are to allow generation and dissipation to be calculated correctly. Simple empirical values can be calculated using equations in the UG but TI can be measured from an experimental rig.

Ebrahim April 11, 2008 03:36

Re: velocity inlet and pressure outlet
what do you mean by 'you need to know what the turbulence conditions are '

i'm solving with and k-epsilon turbulence model, that's why i need to calculate kin energy and dissip.

red lemon April 16, 2008 17:44

Re: velocity inlet and pressure outlet
turbulence energy is brought into the domain via the bc's. These are needed as an entry condition for the calculation. Is flow at the inlet turbulent? If yes, you need need to quantify it and define it. If no then it is run as laminar.

Angela April 28, 2008 22:24

Re: velocity inlet and pressure outlet
Hey, Ebrahim! About this question, i recommand you to read this paper which contains the most general adopted experience equ about k and e ----W. Rodi, Turbulence models and their applications in hydraulics " A state of the art review, IAHR, delft, The Netherlands,1980 In fact, there exists no accurate calculation equ of k and e. Most common equ is k=3/2*(uI)^2 , I=0.16(Re)^-1/8, e=C*^3/4 * k^3/2 /(0.07L) C*=0.09 and L is the characteristic length of your inlet model geometry. For the outlet con, the existence of back flow is due to your case's operation states. In my case the system pressure is bigger than the atm.pressure and my study poin is only a part of the all system. So there is no back flow for the outlet con. In this case, i think you can set k and e for outflow to zero. You can also have a try calculation to know if there exist back flow in your outflow. And then set those value to your specific case as boundary condition.

opop002 January 15, 2015 18:14

can anyone tell me how to assign a temperature profile to an outflow BC in ansys or apply a velocity profile to a pressure outlet

All times are GMT -4. The time now is 16:31.