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January 23, 2013, 12:55 
PressureinletOutletVelocity&Total pressure

#1 
Senior Member
Sasan Ghomi
Join Date: Sep 2012
Location: Iran  Tehran
Posts: 185
Rep Power: 6 
Hi every body
I have a question about a boundry that boundry condition for velocity is type pressureInletOutletVelocity; phi phi; value uniform (0 0 0); (what is this?????) and for pressure is : type totalPressure; U U; phi phi; rho none; psi psi; gamma 1.4; p0 uniform 1e5; value uniform 1e5; (what is this?????) I know that for pressure we have : P0=P+(0.5) (rho )(U^2) what is the value for velocity and pressure?????? Also I know pressureInletOutletVelocity = inletOutlet+ PressureInletVelocity Can any one explain this boundry condition exactly?????? please help me.... 

January 24, 2013, 05:31 

#2 
Senior Member

Dear Sasan,
The pressureInletOutletVelocity is indeed a combination of inletOutlet and pressureInletVelocity. It means that in case there is an outward flux, the boundary condition is zeroGradient, extrapolating from the internal field outwards, if the flux is inwards to the cell, the pressure is used to determine the magnitude of the patchnormal velocity, similar to the way pressureInletVelocity is used. The entries in "value" are basically initial values (for the velocity vector, or the static pressure), that get updated during the first iteration/timestep, so they need to be appropriate. If you have an estimate to what either of them should be, then you can use those values, but the current setup seems fine to me. Regards, Tom 

January 24, 2013, 11:27 

#3 
Senior Member
Sasan Ghomi
Join Date: Sep 2012
Location: Iran  Tehran
Posts: 185
Rep Power: 6 
Hi Tom,
thanks for your reply.. But I have two questions: 1)when we have outwards flux the boundry condition for velocity is zeroGradient and what is the role of extrapolation in this boundry???Do you mean that in this boundry the boundry condition is zeroGradient and boundry value evaluated by extrapolation from internal field????? 2)You said , when we have inwards flux the velocity evaluates from pressure but in this case the pressure is dependent on velocity (P0=P+(0.5) (rho )(U^2))...Can you explain more about it? thanks, Sasan. 

January 24, 2013, 12:44 

#4  
Senior Member

Hi Sasan,
Quote:
Quote:
I hope this answers your questions? Regards, Tom 

January 24, 2013, 14:33 

#5 
Senior Member
Sasan Ghomi
Join Date: Sep 2012
Location: Iran  Tehran
Posts: 185
Rep Power: 6 
Dear Tom,
I got it...But please answer my last question : I think all of the iterative methods (PISO/SIMPLE/PIMPLE) need to have specified value(or specified condition) on boundaries....please correct me if I am wrong...???????? I want to conclude in this case that the boundry value is not fixed in all of the solution's time and the boundry value evaluates at each time step (by iterative procedure).... Is my conclusion correct?? thanks, Sasan. 

January 25, 2013, 04:07 

#6 
Senior Member

That is indeed the case. The only thing that is fixed is the total pressure, only static and dynamic pressure will change between time/iteration steps.


January 25, 2013, 06:09 

#7 
Senior Member
Sasan Ghomi
Join Date: Sep 2012
Location: Iran  Tehran
Posts: 185
Rep Power: 6 
Dear Tom,
thank you very much Sasan. 

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