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Average total hydraulic head through a baffle

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Old   February 16, 2017, 07:33
Default Average total hydraulic head through a baffle
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Nicoḷ Pozzani
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Hello everyone,

I'm a student writing the master thesis in environmental engineering. I'm working with FLOW-3D to study the interaction between a free surface current and a hydraulic loss by a baffle with some other components.

I used even some other baffles in order to have as output the average value of the total hydraulic head through them. But when I study the text output through the same section i don't find the same values of the total hydraulic head averaged, specially when the kinetic energy is considerable. When it's not i can find almost the same value.

So can you explain me how the software compute the total hydraulic head generally? and how it does that through the baffle?

thanks
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Old   February 16, 2017, 17:51
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brian
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There is some information on hydraulic head in FLOW3D at: https://www.flow3d.com/hydraulic-energy-losses/

The flux average hydraulic head is basically a discharge weighted average of the hydraulic head across the baffle. To summarize:

Hydraulic energy e = P + |g| ρ z + ρ (u^2 + v^2 + w^2)/2 .... units of pressure (force/unit area)

Total hydraulic head h = e/(|g| ρ) .... units of length (height of a water column)

THEAD1 (at a baffle) = ∑(q e)/[ρ |g| ∑(q)] .... units of length, and the summation is of the flux across a baffle cell face, and that flux is the average of the upstream and downstream cell, and is signed.

q = volumetric flux
g = gravitational acceleration, typically calculated from GZ, GY, GZ
ρ = fluid density, typically RHOF unless variable density option is used
P = pressure, typically from GRMES solver
z = elevation above a reference. In FLOW-3D, this elevation used to be above the z-min boundary.
u,v,w = velocity components in x,y,z directions.
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Old   February 23, 2017, 11:35
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Nicoḷ Pozzani
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thank you so much bfox48. I've another question.

I'm flowing water through a circular section, with a known area minor than the channel's area. In that section i also set the baffle with the head loss with a quadratic coefficient so i could know, from k*u^2/2g the theoretical head loss cause the u is known. But I even set two other baffles just before and after that section.

My problem is: if i check the total hydraulic head by those two baffles, the head loss difference between them is higher than the k*u^2/2g value, which should be known.

Do you think that i can take the k*u^2/2g head loss as the real one and then the difference between the other two baffles as the summation of the baffle head loss and the shrinkage due by the circular section?
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Old   April 21, 2017, 15:30
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Saeed Nazari
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hi,I'm a new user of Flow-3d
i'm studing on labyrinth spillways and trying to simulation of labyrinth weirs,
so I have a question
whats the different of total hydraulic head and total hydraulic head 3d and specific hydraulic head
with the best regurds
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