ACCELERATE
   ZONE n
   [SECOND START iter1 END iter2]
   [FOURTH START iter1 END iter2]
   [CFLRAMP START iter1 END iter2]
ENDACCELERATE

The objective of WIND's convergence acceleration scheme is to approach the steady state solution more quickly by allowing the use of a large CFL number early in the calculation, adding second- and fourth- order smoothing to maintain numerical stability. This option must be used in conjunction with the SMOOTHING keyword and TEST 49.

This keyword does not work when CFL# MODE 3 (i.e., the time step calculation procedure from OVERFLOW) is used.

iter₁ and iter₂ specify the starting and ending iteration values for the corresponding keyword parameter. The CFL number will be ramped down linearly from its starting value, specified using the CFL# keyword, to 1.0.

The ZONE keyword identifies the zone within which convergence acceleration is to be used. If convergence acceleration is to be used in multiple zones, and/or if different starting and ending iteration values are to be used in different zones, multiple ZONE keywords must be specified.

If starting and ending iteration values are not specified, the following default values are used:

	Option		iter1		iter2
	SECOND		1		150
	FOURTH		50		500
	CFLRAMP		50		500

Example

In the following example, convergence acceleration is applied in zones 3 and 4. Second-order smoothing is applied between iterations 1 and 200, and fourth-order smoothing is applied between the default values of iterations 50 and 500. The CFL number specified with the CFL# keyword will be used for the first 250 iterations, then ramped down to a value of 1.0 between iterations 250 and 500.

   SMOOTHING SECOND s1 FOURTH s2 SMLIMT 0.
   ACCELERATE
      ZONE 3
      ZONE 4
      SECOND START 1 END 200
      CFLRAMP START 250 END 500
   ENDACCELERATE
   TEST 49 2