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-   -   Bellmouth Modelling (http://www.cfd-online.com/Forums/floefd-floworks-flotherm/27205-bellmouth-modelling.html)

 Mike Brown November 10, 2008 15:02

Bellmouth Modelling

Hopefully someone here finds this very easy and can offer tips. I'm trying to model the flow of water being sucked into a pipe bellmouth from infinate water supply like a lake. So far i've set up a thin feature 2m x 2m x 2m (30mm Thick) box around the bellmouth where the water is. I've capped the end of the tube to which the bellmouth is attached and applied a sucking flow on the inside surface of this. My main problem is defining the water. The box would need to simulate the lake, therefore the top is at atmospheric pressure. The sides would be under hydrostatic pressure and the base the pressure 2m below the surface. This doesn't work however. Any tips would be largely appreciated. cheers mike

 Matic Grom November 11, 2008 04:00

Re: Bellmouth Modelling

Hi,

As i understand you, you are trying to specify two boundary conditions as pressure openings? A also tried this sort of simulations in FloWorks, for example flow through piping systmes and it does not work. As much as I found out, you have to specify pressure opening and flow opening (outflow, inflow or velocity).

So my suggestion is, that you assume some outflow and run simulation. Then you check pressure on outflow opening. If it has value you would specify simulation is completed. If not, specify new outflow condition. You do that until pressure on outflow opening is equal (in reasonable tolerance) to pressure, you want to specify as outlet pressure.

I hope I helped.

Cheers

Matic

 Mike Brown November 11, 2008 11:39

Re: Bellmouth Modelling

Sorry Matic, I'm not trying to specify two boundary conditions as pressure openings, i was just explaining what i've done so far which is wrong. I'm trying to model the water flow around a bellmouth intake to a pump. Looking at how adjusting the shape of the bellmouth effects the fluid flow into it. Unfortunately Flowworks only allows internal flows such as pipe systems. To find a way around this i tried creating an infinate space around the bellmouth to simulate the water source. However, this is a lot harder than i thought.

 Ive November 14, 2008 05:24

Re: Bellmouth Modelling

FloWorks is capable of simulating external flows as long as they do not involve free surfaces. You can solve your problem either as external or internal. For external problem, create your pipe as a channel in a massive of solid (i.e. as a cylindrical cut in a solid cube ). For example, if you want to calculate the flow in a 2x2x2 m cube near the bellmouth, your solid should have the section of 2x2 m and the pipe's length in the third dimension. Then specify the project in Wizard as external, don't forget to enable the Gravity physical feature in the direction of the coordinate axis defining the depth of the lake. On the Initial conditions step of the Wizard specify the pressure of 1 atm if the origin of your coordinate system is located at the top surface of volume or the pressure at the depth of 2 m if the origin is located at the depth level of 2m. Make sure that the Pressure potential check box is selected. Together with Gravity enabled this will provide the pressure gradient due to the weight of water. After Wizard adjust the computational domain size to include only the solid with channel and some fluid volume adjacent to the bellmouth (not protruding outside the section of solid normal to the bellmouth's axis!). Then cap the pipe's side where the pump is installed with the lid and specify mass or volume outlet flow rate. Now you can solve your project. For internal simulation, you have already done some part of the job by creating the box. You need only to enable Gravity in General Settings in the direction of depth axis, specify the pressure according to the location of origin, as I described above, enable Pressure potential, specify Environment pressure on the inside walls of the box (with the Pressure potential check box selected) and the pump outlet volume or mass flow rate at at the lid.

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