What is the advantage of using a delta form of equation and where could I find more information on this.

thanks.

Dear Unknown...

Please inform us what equation do you mean?

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.

Delta form... Is this Dirac delta-function or something else?

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.

Thanks. I probably used such delta form when solved Poisson's equation for increment of pressure. This is one of steps in SIMPLE-method.

Hi,

Can you provide some reference.

Thanks

Apurva