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January 14, 2013, 16:50 
why UEqn.H of buoyantSimpleFoam has no gravity term?

#1 
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yijin Mao
Join Date: May 2010
Location: Columbia, MO
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This might be silly question, but it confused me a lot..
these snippet code comes from buoyantSimpleFoam of OpenFOAM2.1.1 3 tmp<fvVectorMatrix> UEqn 4 ( 5 fvm::div(phi, U) 6 + turbulence>divDevRhoReff(U) 7 ); 8 9 UEqn().relax(); 10 11 if (simple.momentumPredictor()) 12 { 13 solve 14 ( 15 UEqn() 16 == 17 fvc::reconstruct 18 ( 19 ( 20  ghf*fvc::snGrad(rho) 21  fvc::snGrad(p_rgh) 22 )*mesh.magSf() 23 ) 24 ); 25 } shouldn't be this? 3 tmp<fvVectorMatrix> UEqn 4 ( 5 fvm::div(phi, U) 6 + turbulence>divDevRhoReff(U) 7 ); 8 9 UEqn().relax(); 10 11 if (simple.momentumPredictor()) 12 { 13 solve 14 ( 15 UEqn() 16 == 17 fvc::reconstruct 18 ( 19 ( 20  ghf*fvc::snGrad(rho) 21  fvc::snGrad(p_rgh) 22 )*mesh.magSf() 23 ) 24 + rho*g 25 ); 25 } 

January 14, 2013, 17:38 

#2 
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Anton Kidess
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No, the gravity term is hidden in between the usage of p_rgh and ghf*snGrad(rho). There is a thread on the forum with the derivation.
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January 14, 2013, 18:12 

#3 
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Marco A. Turcios
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For bouyancy driven flows that is why we use p_rgh instead of p. If prgh = p + rho*g*h, then when we do grad p in the NS equations we get grad(p) and rho*g. I don't do a lot of buoyancy driven flow so I'm not 100% on the notation.


January 14, 2013, 18:14 

#4 
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yijin Mao
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thanks for your reply.
I derived, but may not correctly, so I did not see the term of rho*gravity. How can I find that thread? some keywords are quite helpful. 

January 14, 2013, 18:18 

#5 
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yijin Mao
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Thanks! I got the idea. I mistakenly took grad(rho*g*h) = grad(rho)*g*h without caring rho*g*grad(h), which equals to rho*g. Shame on me!


January 15, 2013, 03:53 

#6  
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Anton Kidess
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Quote:
Problems in understanding BuoyantBoussinesqSimpleFoam
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October 22, 2013, 13:35 

#7 
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Christiano Molossi
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Hello!
I'm new to OpenFOAM, I started using about 1 month ago. And I have created and account here just now. So i didn't know if it was better to create a new topic or just replay an old one since my doubt is related to this topic. So, I'm working on a simulation with the twoLiquidMixingFoam solver. And just like the UEqn.H posted here before, there is this: * mesh.magSf(). I would like to know what it is, what does it for? What this meaning? Besides this, I want to learn the mathematical modelling form OpenFOAM, for example, in twoLiquidMixingFoam, what is the equations that the solver use to run? If someone could me introduce to a book or anything that may help me to understand the math from this software I would be very thankful. Best regards! 

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