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Old   April 10, 2008, 11:51
Default velocity inlet and pressure outlet
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Ebrahim
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Hey,

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!
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Old   April 11, 2008, 03:30
Default Re: velocity inlet and pressure outlet
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red lemon
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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.
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Old   April 11, 2008, 03:36
Default Re: velocity inlet and pressure outlet
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Ebrahim
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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.
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Old   April 16, 2008, 17:44
Default Re: velocity inlet and pressure outlet
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red lemon
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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.

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Old   April 28, 2008, 22:24
Default Re: velocity inlet and pressure outlet
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Angela
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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.
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Old   January 15, 2015, 18:14
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Olubunmi
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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
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