# discretized form for advection term

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 September 2, 2004, 22:13 discretized form for advection term #1 jinfeng Guest   Posts: n/a Anybody knows when to use conservative form for the advection term or non-conservative form by using finite difference method? For imcomprssible flow, it should be no different, am I right? Thanks, Jinfeng

 September 2, 2004, 23:46 Re: discretized form for advection term #2 Junseok Kim Guest   Posts: n/a Even in incompressible flow, for the mass conservation conservative form is prefered.

 September 3, 2004, 02:52 Re: discretized form for advection term #3 Yticitrov Guest   Posts: n/a I'd say it all depend on your criteria for accuracy. If conservation is a criteria then the answer is most likely to use conservation form. There are non-conservative methods that yield space derivatives with smaller truncation error if that is a criteria. Also it should be noted that although a method is conservative it does not necessarily imply accuracy. For instance, you can have an unstable solution that is still conservative. /Y

 September 3, 2004, 03:18 Re: discretized form for advection term #4 Junseok Kim Guest   Posts: n/a I agree with you on that comment. For example, high order Godunov type upwinding method and some ENO type are used, non-conservative form is naturally used. But for the transport of density or volume-fraction, still conservative form is used to preserve conservation of those quantities.

 September 3, 2004, 06:04 Re: discretized form for advection term #5 Salvador Guest   Posts: n/a Well, I think the choice depends on the problems. For compressible flows conservative forms finite volume schemes is the safest choice. Even using high order Godunov. Although with high order schemes it is a question of flavours. MPWENO, entropy-splitting, flux and slope limiters..you name it. In turbulence applications, some schems will dissipate more than others, destroying part of the information, other will dissipate less and therefore oscillate. However, one question I would like to ask, what happened with the advection term in a non conservative equation?, i. e. rdQ/dt + rvdQ/dx where v is a velocity conditioned on some variable, Q is a conditional scalar and r a conditional density, therefore dr/dt + d(rv)/dx is NOT zero Which kind of discretization schemes will be suitable for this term?.

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