rhoCentralFoam: two questions

praveen · October 21, 2012, 02:03

In rhoCentralFoam, there is a line like

https://github.com/OpenFOAM/OpenFOAM...ralFoam.C#L190

Where is this variable used ? It seems like commenting this lines has no effect.

Secondly, here

https://github.com/OpenFOAM/OpenFOAM...ralFoam.C#L196

one sees

fvm:ddt(rho,U) - fvc::ddt(rho,U)

but this equation does not make sense. It seems to me that fvc::ddt(rho,U) is identically zero, as discussed here

http://www.cfd-online.com/Forums/ope...tml#post196210

praveen · October 21, 2012, 02:55

I think I understand the second question.

Solve density equation: $\rho^o \to \rho^n$

Solve momentum equation with only inviscid terms; this gives an intermediate estimate of the velocity $u^o \to u^*$

Update velocity to current time level n by taking account of viscous terms

$\textrm{fvm::ddt(rho,u) - fvc::ddt(rho,u)} = \frac{\rho^n u^n - \rho^o u^o}{\Delta t} - \frac{\rho^n u^* - \rho^o u^o}{\Delta t} = \frac{\rho^n u^n - \rho^n u^*}{\Delta t}$

October 21, 2012, 02:03	rhoCentralFoam: two questions	#1
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	In rhoCentralFoam, there is a line like https://github.com/OpenFOAM/OpenFOAM...ralFoam.C#L190 Where is this variable used ? It seems like commenting this lines has no effect. Secondly, here https://github.com/OpenFOAM/OpenFOAM...ralFoam.C#L196 one sees fvm:ddt(rho,U) - fvc::ddt(rho,U) but this equation does not make sense. It seems to me that fvc::ddt(rho,U) is identically zero, as discussed here http://www.cfd-online.com/Forums/ope...tml#post196210

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October 21, 2012, 02:55		#2
praveen Super Moderator Praveen. C Join Date: Mar 2009 Location: Bangalore Posts: 342 Blog Entries: 6 Rep Power: 18	I think I understand the second question. Solve density equation: $\rho^o \to \rho^n$ Solve momentum equation with only inviscid terms; this gives an intermediate estimate of the velocity $u^o \to u^$ Update velocity to current time level n by taking account of viscous terms $\textrm{fvm::ddt(rho,u) - fvc::ddt(rho,u)} = \frac{\rho^n u^n - \rho^o u^o}{\Delta t} - \frac{\rho^n u^ - \rho^o u^o}{\Delta t} = \frac{\rho^n u^n - \rho^n u^*}{\Delta t}$