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-   -   important: spillway with aerator device (http://www.cfd-online.com/Forums/flow-3d/113673-important-spillway-aerator-device.html)

flow_CH February 25, 2013 01:59

important: spillway with aerator device
 
Hello.

I have very important question.

I have to simulate a spillway with aerator device, in Flow 3D.(for prevention of cavitation)
Can flow 3D simulate this chute with artificial injection air into the ramp?
or the ramp (eg. offset,groove or ...) is
Sufficient for prevention of cavitation?(without injection air into the ramp)
see this pic


Jing_min February 25, 2013 10:23

Quote:

Originally Posted by flow_CH (Post 409863)
Hello.

I have very important question.

I have to simulate a spillway with aerator device, in Flow 3D.(for prevention of cavitation)
Can flow 3D simulate this chute with artificial injection air into the ramp?
or the ramp (eg. offset,groove or ...) is
Sufficient for prevention of cavitation?(without injection air into the ramp)
see this pic


Hi
It seems that the software is not capable of that.
Only free surface aeration is possible.

flow_CH February 25, 2013 10:54

Quote:

Originally Posted by Jing_min (Post 409947)
Hi
It seems that the software is not capable of that.
Only free surface aeration is possible.

are you sure this isn't possible?

Jing_min February 25, 2013 13:40

Quote:

Originally Posted by flow_CH (Post 409961)
are you sure this isn't possible?

As far as I know.
But I would be glad if it happens!!!!!
Please let me know.

flow_CH February 25, 2013 13:59

Is the ramp (eg. offset,groove or ...) Sufficient for prevention of cavitation for simulating in flow 3D?(without injection air into the ramp)

JBurnham February 25, 2013 17:05

You can inject the air using 1-fluid, free-surface flow in several ways. All of them require 'density evaluation: 1st- or 2nd-order approximation to the transport equation' option. I would also use the drift-flux physics.

The air can be injected using a mass-momentum source with density set to that of air. Or it can be entrained using Air Entrainment physics, but that requires calibrating the air entrainment rate coefficient, so I would recommend just using the mass/momentum source. You need to know the rate of air injection for this option. If you don't know the rate of air injection, and can't even guess at it, then you can't model this situation.

I wouldn't recommend using the cavitation model for this case: just look at the pressures near surfaces and check to see if they are below cavitation pressure.

flow_CH February 26, 2013 02:04

someone give me confidence about this modeling, please.

Jing_min February 26, 2013 13:32

Quote:

Originally Posted by flow_CH (Post 410087)
someone give me confidence about this modeling, please.

You can contact FlowScience to have a consult.

flow_CH February 27, 2013 00:53

Is there a difference between the chute with ramp(without injection air into the ramp) and without ramp answers in flow 3D?

flow_CH March 1, 2013 05:24

please help.
someone give me confidence about this modeling, please.

flow_CH March 2, 2013 01:48

Dear all

i just have three monthes to do this project.
Please answer this three questions. Answers to these questions will help me a lot.
1- What points are in this project that distinguish this model from other models? (the models without injection air into the ramp)
2- What boundary conditions should i define into the flow 3D? I think the most difficult parts of the software are boundary conditions and meshing.
3- How air can inject into the ramp?
thanks

dmilano March 4, 2013 11:17

It can be done - trust JBurnham on this one.

flow_CH March 4, 2013 16:21

Quote:

Originally Posted by JBurnham (Post 410027)
You can inject the air using 1-fluid, free-surface flow in several ways. All of them require 'density evaluation: 1st- or 2nd-order approximation to the transport equation' option. I would also use the drift-flux physics.

The air can be injected using a mass-momentum source with density set to that of air. Or it can be entrained using Air Entrainment physics, but that requires calibrating the air entrainment rate coefficient, so I would recommend just using the mass/momentum source. You need to know the rate of air injection for this option. If you don't know the rate of air injection, and can't even guess at it, then you can't model this situation.

I wouldn't recommend using the cavitation model for this case: just look at the pressures near surfaces and check to see if they are below cavitation pressure.

JBurnham: "If you don't know the rate of air injection, and can't even guess at it, then you can't model this situation."

But There is no anything about the rate of air injection in the experimental results that i have. The air entrainment reason is suction of flow velocity or self aeration or something like that. in this situation i can't simulate that?

flow_CH April 6, 2013 06:02

Quote:

Originally Posted by flow_CH (Post 411478)
JBurnham: "If you don't know the rate of air injection, and can't even guess at it, then you can't model this situation."

But There is no anything about the rate of air injection in the experimental results that i have. The air entrainment reason is suction of flow velocity or self aeration or something like that. in this situation i can't simulate that?

Dear all

i just have two monthes to do this project.
please help.
There is no anything about the rate of air injection in the experimental results that i have. The air entrainment reason is suction of flow velocity or self aeration or something like that. in this situation i can't simulate that?

JBurnham April 6, 2013 23:45

You can model self-aeration - but you should calibrate the air rate entrainment coefficient so you get the correct rate of self-entrainment. In order to do that you must have some idea of what the amount of entrained air was in the experiment. Please refer to the User Manual and the air entrainment Tech Note on the FLOW-3D User Site for details on air entrainment at turbulent free surfaces.

flow_CH April 7, 2013 04:11

can flow3d pull the air into the ramp without modeling artificial entrainment of air?


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