- MacCormack method
In
computational fluid dynamics , the MacCormack method is a widely used discretization scheme for the numerical solution of hyperbolic partial differential equations (hyperbolic PDEs). This second-orderfinite difference method is introduced by R. W. MacCormack in 1969. [MacCormack, R. W., The Effect of viscosity in hypervelocity impact cratering, AIAA Paper, 69-354 (1969).] The MacCormack method is very elegant and easy to understand and program. [Anderson, J. D., Jr., Computational Fluid Dynamics: The Basics with Applications, McGraw Hill (1994).]The algorithm
The MacCormack method is a variation of the two-step Lax–Wendroff scheme but is much simpler in application. To illustrate the algorithm, consider the following one-dimensional linear wave equation:The application of MacCormack method to the above equation proceeds in two steps; a "predictor step" which is followed by a "corrector step".
Predictor step: In the predictor step, a "provisional" value of at time level (denoted by ) is estimated as follows:It may be noted that the above equation is obtained by replacing the spatial and temporal derivatives in the wave equation using forward differences.
Corrector step: In the corrector step, the predicted value is corrected according to the equation :Note that the predictor step uses backward finite difference approximations for both spatial and temporal derivatives. Note also that the time-step used in the corrector step is in contrast to the used in the predictor step.
Replacing the term by the temporal average:to obtain the corrector step as:
Some remarks
The MacCormack method is well suited for nonlinear equations (Inviscid
Burgers equation ,Euler equations , etc.) The order of differencing can be reversed for the time step (i.e., forward/backward followed by backward/forward). For nonlinear equations, this procedure provides the best results. For linear equations, the MacCormack scheme is equivalent to the Lax–Wendroff scheme. [Tannehill, J. C., Anderson, D. A., and Pletcher, R. H., Computational Fluid Dynamics and Heat Transfer, 2nd ed., Taylor & Francis (1997).]Unlike first-order
upwind scheme , the MacCormack does not introduce diffusive errors in the solution. However, it is known to introduce dispersive errors (Gibbs phenomenon ) in the region where the gradient is high.See also
*
Lax-Wendroff method
*Upwind scheme
*Hyperbolic partial differential equation sReferences
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