[Svensen]

Hi,


normally, we impose velocity at inlet and pressure at outlet.


If I want to use flowRateOutletVelocity at outlets, what should be for an inlet? zeroGradient?



What I should impose for pressure at inlet and outlets? All patches are zeroGradient ? But this doesn't work....


Any suggestions ?



Thanks.

[oswald]

Hi Svensen,


zeroGradient for the inlet velocity might be okay, you could also try pressureInletOutletVelocity. For the pressure you should then set a fixedValue at the inlet.

[Svensen]

I only know inlet flow rate and outlet flow rates.
For inlet, I could not set a pressure level, since it is varying during time.
For outlet I could set only zero pressure level.

But I think it is not sufficient.

inlet:

u - inlet flow rate;
p - zero gradient;

outlets:

u - outlet flow rate;
p - 0;

Is it what you mean ?

[oswald]

You should provide some kind of fixed velocity value (whatever name the BC has) at one boundary, be it inlet or outlet. The other one should be zero gradient. For example:

Inlet: U --> zeroGradient; p --> fixedValue;
Outlet: U --> flowRateOutletVelocity; p --> zero Gradient

Is your flow incompressible or compressible?

[anil.istanbullu]

Originally Posted by oswald

You should provide some kind of fixed velocity value (whatever name the BC has) at one boundary, be it inlet or outlet. The other one should be zero gradient. For example:

Inlet: U --> zeroGradient; p --> fixedValue;
Outlet: U --> flowRateOutletVelocity; p --> zero Gradient

Is your flow incompressible or compressible?

No need to remind that compressible flow requires the user to go with mass flow rate due to compressibility effects, otherwise the analysis would not most likely converge at the end.

When it come to incompressible fluids, it is comperatively easy to identify BC's since volumetric flow rate come in handy anyway.