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Condition of Air velocity in Open Channel simulation

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Old   May 9, 2014, 05:08
Default Condition of Air velocity in Open Channel simulation
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Baek, Donghae
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I am simulating Curved Open channel using VOF(interFoam) in 3D

my assumption is that

- air is static at initial ( velocity of air = zero )
- velocity of water at inlet is defined as fixed uniform value
- the air will have velocity magnitude as time goes on due to friction on free surface

following assumption above,

inlet patch is splitted two part (air and water).

the boundary condition of velocity is that:

inlet@water : fixedValue
inlet@air : zeroGradient or pressureinletoutletvelocity

outlet@water : zeroGradient or fixedvalue (same to inlet)
outlet@air : zeroGradient or pressureinletoutletvelocity

atmosphere : pressureinletoutletvelocity

the boundary condition of pressure(p_rgh) is that:

inlet, outlet, sidewall : buoyantpressure
atmosphere : total pressure

however I haven't got reasonable result from that setting.

I constructed another setting stopping simulation of that.

I gave velocity magnitude to inlet@air. the value is identical to inlet@water.

for example ,

if water velocity is 2 m/s @inlet, the air velocity is also 2 m/s @inlet.

the result of that setting is surprisingly reasonable comparing with experimental data.

but I still don't understand it.

actually the setting of latter is somehow physically uncommon.

it is rare that the velocity is same both water and air.

as far as I know, many people already simulated open channel case like that setting (V_air@inlet and V_water@inlet are same)

I wonder that setting is physically reasonable or not.
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