fix outflow bc for boundary normal velocities. #1374
Merged
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The face centered velocity located on an outflow boundary must be treated differently. The FOEXTRAP causes an erroneous update for normal velocity at the boundary; this sustains a very small boundary velocity that does not relax to the adjacent flow field inside the domain.
This PR modifies the outflow BC to utilize a second order Neumann condition to specify the boundary value. The source for the stencil is as follows:
Simulating in Exec/Regtests/Bubble with inputs_BF02_moist_bubble shows that the contours in xvelocity are no longer suppressed at the boundary or within the domain: