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[Basic Vocabulary] Buoyant fluid

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Old   August 21, 2012, 04:41
Default [Basic Vocabulary] Buoyant fluid
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m_f
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Hello,

I am a french user, and I don't understand the signification of "buoyant", particularly when a fluid is described as a "buoyant fluid". I search with google, but I found definition which hadn't a physic signification. Is the same as in French "un fluide non pesant" ? How to traduce this adjective in French ? (I need an adjective ^^)

Thanks for any hint,
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m_f
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Old   August 21, 2012, 05:20
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Babylon suggests the English synonym "floating" (and "flottant" in French).
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Old   August 21, 2012, 07:17
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Ok, but what does it mean physically ? Which is the equation concerned ? Which term is neglected if the fluid isn't buoyant ?
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Old   August 21, 2012, 08:13
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A buoyant fluid is subject to forces caused by gravitation and variable density.
Natural convection would be a typical phenomenon for such a kind of fluid. But I really dont know a catchy french adjective for this. Even had trouble finding a german word for it.

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Old   August 21, 2012, 09:17
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Quote:
Originally Posted by m_f View Post
Ok, but what does it mean physically ? Which is the equation concerned ? Which term is neglected if the fluid isn't buoyant ?
Physically "buoyancy" is related to gravity and differences in density. It manifests itself in the momentum equations and possibly in the energy and turbulence equations (if they exist). Under some limitations, the Boussinesq approximation (please look it up) is used in the momentum equation.
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Old   August 21, 2012, 09:33
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Mmmh. Ok, It's what I understood during my research..I will continue to search my adjective !
If someone else have an idea...

Thanks for your quick answer and for your help

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Old   August 21, 2012, 12:41
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Quote:
Originally Posted by m_f View Post
Ok, but what does it mean physically ? Which is the equation concerned ? Which term is neglected if the fluid isn't buoyant ?
Hi , buoyancy force only occurs when you have a flow with variable density due to temperature, concentration or when you have two phase-flow(gas-liquid or liquid-liquid immiscibe fluids). When the fluid is monophase with constant density this force has no effect on the flow itself. It is then incuded in the driving pressure P+rho*g*z
The buoyancy force is rho*g (g here is the gravity vector) it is included in the momentum equation as source term.
Rho may depend for example from temperature or concentration.
Then you must have an expression which tells you how rho evolves with this variable. For example for liquids you can choose
rho=rho0(1-beta(T-T0)) or rho=rho0(1-beta(C-C0)) in case of mixing fluids
Then you have the ernergy equation which allows you to compute the temperature or transport equation for concentration.
These equations are coupled with the momentum equation through rho.
If you consider the boussineq assumption.Then rho =rho0 every where in the momentum equation except in the buoyancy term rho*g

I would use "fluid pesant" for buoyant fluid in french.
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Old   August 21, 2012, 14:51
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Thanks a lot for you complete anwser.

Best_regards,

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