Specifies how the reverse flow direction will be computed.

Boundary Normal

Assumes the incoming flow is normal to the boundary. It is the default option and will generally provide the most robust convergence, unless the flow is largely parallel to the boundary, in which case the Extrapolated option should be used.

Extrapolated

Extrapolates the flow direction from the interior of the domain. In most situations, this will be less stable than the Boundary Normal option. However, it is recommended for situations where the flow is known to be parallel to the pressure boundary, such as a co-flowing jet.