# p, p_rgh and buoyant pressure

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 January 9, 2013, 17:39 p, p_rgh and buoyant pressure #1 Senior Member     ahmed Join Date: Feb 2010 Posts: 161 Blog Entries: 1 Rep Power: 7 Dear foamers, why we define p, and p_rgh in some cases and don't define only one? what is the difference in buoyant pressure boundary condition? thanks in advance.

 January 11, 2013, 10:33 #2 Member   Jianye Xia Join Date: Mar 2009 Posts: 32 Rep Power: 8 I have the same question, can anyone help to explain these items?

 January 11, 2013, 17:05 #3 Senior Member   Join Date: Nov 2012 Posts: 168 Rep Power: 4 Hi, According to my understanding, p is the total pressure, p_rgh is the hydrodyunamic pressure, actually, there should another pressure-therdynamic pressure. For low speed flows or for low ma assumption, p=rho*g*h + thermodynamic pressure. For compressible cases, p=rho*g*h + thermodynamic pressure + p_rgh. In the former case, the pressure appearring in EoS and the pressure appearring in momentum are not the same quantity. If we do not take the boyuance, rho*g*h can be removed. We can also call the thermodynamic pressure as background pressure.

 January 23, 2013, 05:16 #4 Senior Member     ahmed Join Date: Feb 2010 Posts: 161 Blog Entries: 1 Rep Power: 7 Hi every body, we all know that p = p_rgh + rho*g*h. but it this case both p, p_rgh are defined, so which variable is calculated from the other, we can define only one. the other question which one of them is used in N.S equations or energy eqn (i noticed that p_rgh is used). another thing we know that p expresses total pressure and rgh expresses hydrostatic pressure, so the difference expresses the dynamic pressure which can be used for calculation velocity which already an input. I'm really confused ?? thanks

January 23, 2013, 14:16
#5
Senior Member

ahmed
Join Date: Feb 2010
Posts: 161
Blog Entries: 1
Rep Power: 7
Dear Foamers,

Quote:
 Modifications to multiphase and buoyant solvers Multiphase and buoyant flow solvers now solve for , rather than the static pressure p. This change is to avoid deficiencies in the handling of the pressure force / buoyant force balance on non-orthogonal and distorted meshes. Improvements to boundary conditions and pressure referencing in closed domains have been developed to avoid the problems encountered in previous attempts to decompose pressure for buoyant flow.

my question is if OPreplaced p by p_rgh why we still define p in input files.

thanks

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