[ingenium]

Hello Community,

I have the following problem:

• I calculate a closed system consisting of a conical tank and a pump (see the picture in attachment).

• In the tank is fluid with different viscosities.

• The pump circulates the quite etransient.

I am reluctant to model the pump as a rotating mesh because it is too complex from my point of view. Can I replace the pump with boundary conditions ?


P.S.: I'm working with ANSYS fluent 2020 R1.

[LuckyTran]

Use a volumetric momentum source. It is not my intent to tell you exactly what to do from here, but look into it and come back with questions as they become pertinent because it's not as simple as it sounds.

[ingenium]

Originally Posted by LuckyTran

Use a volumetric momentum source. It is not my intent to tell you exactly what to do from here, but look into it and come back with questions as they become pertinent because it's not as simple as it sounds.

Thank you for the advice. Is it possible with this type of modeling to pump the fluid I squeeze out of the outlet back into the inlet ?

[LuckyTran]

Does your mesh include the pump runner or not? If not, and you have just a tank, then you can use outlet and inlet BC's. But you can't use BC's where there are no boundaries.

[ingenium]

Originally Posted by LuckyTran

Does your mesh include the pump runner or not? If not, and you have just a tank, then you can use outlet and inlet BC's. But you can't use BC's where there are no boundaries.

No, I specifically don't want to include the impeller because I'm only interested in the flow in the tank.



I would like to couple the bc so that the flow is reinjected from intlet into the outlet at different temperatures.
Initial is in the tank flow with two temperatures and viscosities. The pump mixes the whole thing. I would like to investigate the influence of the nozzle angle. Therefore, the pump does not interest me at all.

[LuckyTran]

Oh okay. In that case, then the volumetric source is not applicable at all. You can use an outlet and inlet BC.

Usually you would use a pressure inlet and pressure outlet. You would specify the inlet and outlet pressures corresponding to pressure rise across the pump if that was the parameter you knew. If you knew the flow rate, you would then use the targeted mass flow rate option for the pressure outlet. There are some other pairs of BCs that will still work, such as a mass flow inlet and pressure outlet.

[ingenium]

Originally Posted by LuckyTran

Oh okay. In that case, then the volumetric source is not applicable at all. You can use an outlet and inlet BC.

Usually you would use a pressure inlet and pressure outlet. You would specify the inlet and outlet pressures corresponding to pressure rise across the pump if that was the parameter you knew. If you knew the flow rate, you would then use the targeted mass flow rate option for the pressure outlet. There are some other pairs of BCs that will still work, such as a mass flow inlet and pressure outlet.

But how do I tell the program that what comes out from the outlet goes exactly into the inlet ?


The inlet boundary condition is not constant.

[LuckyTran]

You don't need to. Everything that flows in must come out. Local continuity implies global continuity. All you need to do is make sure you have a meaningful pressure level.

[ingenium]

Originally Posted by LuckyTran

You don't need to. Everything that flows in must come out. Local continuity implies global continuity. All you need to do is make sure you have a meaningful pressure level.

Sorry if I'm being silly, but there's one thing I don't understand. I have attached a sketch of the system.
I have a pressure in the inlet BC that pushes the flow out of the outlet. But the flow out of the outlet changes over time because the temperature fields mix. In the inlet, however, I specify a temperature. In my understanding, I pump the fluid into the inlet with always constant temperature. However, it does not come out of the outlet at a constant temperature.
I should actually take the temperature distribution from the outlet and feed the same temperature distribution back into the inlet.