# Delta form of equations.

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 March 3, 2004, 15:38 Delta form of equations. #1 unknown Guest   Posts: n/a What is the advantage of using a delta form of equation and where could I find more information on this. thanks.

 March 3, 2004, 22:01 Re: Delta form of equations. #2 Michail Guest   Posts: n/a Dear Unknown... Please inform us what equation do you mean?

 March 4, 2004, 01:29 Re: Delta form of equations. #3 versi Guest   Posts: n/a I remeber that the advance of a delta form discrete matrix equation is the independence of steady state solution on time step. T. H. Pulliam's book may contain it as well as in other CFD books.

 March 4, 2004, 02:16 Re: Delta form of equations. #4 ZZ Guest   Posts: n/a Delta form... Is this Dirac delta-function or something else?

 March 4, 2004, 10:05 Re: Delta form of equations. #5 ag Guest   Posts: n/a In the delta form of the equations you are solving for the incremental change of the dependent variables. For example you can write a second-order time difference as du/dt = (3u(n+1 - 4u(n) + u(n-1)/2dt or du/dt = 1.5*(du(n+1) - (1/3)*du(n))/dt where du(n+1) = u(n+1) - u(n), du(n) = u(n) - u(n-1). It's the same equation, but the delta form is better behaved because typically the delta quantities are small changes and the resulting equations are more robust.

 March 4, 2004, 12:30 Re: Delta form of equations. #6 ZZ Guest   Posts: n/a Thanks. I probably used such delta form when solved Poisson's equation for increment of pressure. This is one of steps in SIMPLE-method.

 March 8, 2004, 08:46 Re: Delta form of equations. #7 Apurva Guest   Posts: n/a Hi, Can you provide some reference. Thanks Apurva

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