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Reduction Factor & Sweep (CFX-4)

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Old   August 19, 2005, 10:50
Default Reduction Factor & Sweep (CFX-4)
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Hello, can someone explain the usage of reduction factor & sweep. For example, when to use it and how to use it?

Thanks. Joan
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Old   August 20, 2005, 10:56
Default Re: Reduction Factor & Sweep (CFX-4)
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Usually when a problem isn't converging on the outer iterations (the residual plot), it is an indication that one or more of the inner loops is not converging.

The inner "sweeps" continue until the variable residual is reduced to a factor of its initial value. Sweeps will continue until the reduction factor is met (0.25 for U,V,W and 0.1 for P) or the "Maximum Number" of sweeps is reached ( 5 for U,V,W and 30 for pressure. These defaults are set to ensure that mass (Pressure) is very tightly converged on each iteration. The other variables usually follow.

You can turn on SOLVER DEBUG PRINTING under >>PROGRAM CONTROL to see how these inner sweeps are behaving (output is printed to an extra file).

If some variables aren't getting to their required REDUCTION FACTOR, you may want to increase the MAXIMUM NUMBER of sweeps under >>SWEEPS INFORMATION to allow those equations to converge more tightly. If you need even tighter contvergence on an equation, you can lower its REDUCTION FACTOR to something below its default value.

Of course if everything is converging, you don't need to mess with any of these parameters at all.

See Section 6.3 in the Flow Solver User's Guide for more on this topic.

Hope this helps, Jeff
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