Suppose the differential equation is a pure advection equation,

\fraction{\partial C}{\partial t} = u \fraction{\partial C}{\partial x}

And suppose CFL number is known, how to calculate time step \Delta t?

Thanks a lot.

Annie

\Delta t = CFL* \Delta x

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u

For pure advection equation, the time step will be calculate from next relation: Dt=CFL*(Dx/u) where Dt is time step, Dx is spatial step, 0<CFL<1.

In Compressible Flow Problem We calculate the Time step Value Using CFL Correlation. But in Incompressible Flow Problem How we calculate the Time step?.. What is the Physics Behind that?..

Thanks.... Yousuf

If the flow is inviscid or you're using an explicit time integration scheme it is calculated exactly the same way in compressible and incompressible flows. The material derivative is a hyperbolic operator which implies a CFL restriction.