# Flow through Water Intake Bays

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December 20, 2017, 23:51
Flow through Water Intake Bays
#1
New Member

Niveshram
Join Date: Aug 2016
Posts: 5
Rep Power: 8
Hello All,

I am trying to model flow of water, in a multiple intake pump bay.

The Intake bay is rectangular shaped which has 4 pumps on one side for flow intake and 1 pump on another side.

The Mass flow rate of each pumps are known, however the suction pressure is an unknown parameter.

I have proceeded by giving

Opening Boundary condition with total pressure and direction at Inlet.
Zero gradient mass momentum option is given.
The bay takes in water from the sea/river which is located nearby and it is directly connected to it via a open channel.

The outlet boundary condition specified are individual mass flow rates at each pump station.

The a photo is attached showing the water intake bay and the boundary condition given at inlet.

Can someone tell me whether the given boundary conditions are correct.

As I get the velocity of flow at my inlet in the range of 900-1000 m/s.

Attached Images
 Boundary conditions.jpg (82.5 KB, 35 views)

 December 27, 2017, 17:46 #2 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,713 Rep Power: 25 1) Why do ask this question in freelance menu, and not in the general ANSYS-CFX menu? 2) You put a relative pressure on the inlet equal to 1 atm on the inlet. This is relative to your Reference Pressure. If this is also 1 atmosphere, then your inlet pressure is 2 atm. 3) I would set a total pressure of 0 Pa. Then you need to determine the static pressures yourself from the results file, but that should not be a problem. 4) Depending on the velocity that you will obtain, the inflow into the pump intake will be far from optimal. Shouldn't you include more of the pump intake downstream? Regs, Gert-Jan

December 27, 2017, 22:54
#3
New Member

Niveshram
Join Date: Aug 2016
Posts: 5
Rep Power: 8
Quote:
 Originally Posted by Gert-Jan 1) Why do ask this question in freelance menu, and not in the general ANSYS-CFX menu? 2) You put a relative pressure on the inlet equal to 1 atm on the inlet. This is relative to your Reference Pressure. If this is also 1 atmosphere, then your inlet pressure is 2 atm. 3) I would set a total pressure of 0 Pa. Then you need to determine the static pressures yourself from the results file, but that should not be a problem. 4) Depending on the velocity that you will obtain, the inflow into the pump intake will be far from optimal. Shouldn't you include more of the pump intake downstream? Regs, Gert-Jan

1) Yes I have posted the same query on ansys cfx general too. I didnt know earlier about the separate forum existing for the same work. Sorry for the trouble.

2)Oh ok. Didn't know that, will update model to make inlet pressure as 2 atm. However I am bit confused here. The water intake is from a river flowing downstream into the bay via a canal. So the entire setup is similar to a open to atmosphere flow. Wouldn't that not be equal to 1 atm.

4 ) Yes, what you are saying is 100% correct, I have given mass flow rate at exits and observed that my velocity of fluid seems to drop to zero a few places near pump suction for the isolated pump on one side.

Sorry for the trouble.

 December 28, 2017, 17:56 #4 Senior Member   Gert-Jan Join Date: Oct 2012 Location: Europe Posts: 1,713 Rep Power: 25 2) No you misunderstood me. I suppose you have set a relative pressure of 1 atm and an inlet pressure of 1 atm. Itf so then your inlet pressure equals 2 atm absolute pressure. This is of course unreal, since it should be atmospheric. Therefore you should set your relative pressure equal to 1 atm and your inlet pressure equal to 0 Pa. That sums up to 1 atmosphere. For the inlet pressure can either select a static pressure or a total pressure equal to 0 Pa. You will find that setting a total pressure is much more stable. 4) Possibly the inflow of your pump intake is not within specifications. You might need to take rigourous measures to fix it. If you need help, let me know. As you might guess, I am a freelancer............ Regs, Gert-jan