[roth]

In 1.5.x, the fan boundary condition allowed a negative pressure jump across a cyclic patch. That is, with something like this for pressure

{
    type          fan;
    patchType     cyclic;
    f             List<scalar> 3(0.0 0.0 -1.0);
    value         uniform 0;
}

we would get a porous jump, here delta p = -1.0 V^2

However, in 1.6.x & 1.7.x it appears that the jump is not allowed to drop below zero. i.e. in fanFvPatchFields.C we now have

-- snip --
        for(label i=1; i<f_.size(); i++)
        {
            jump_ += f_[i]*pow(Un, i);
        }

        jump_ = max(jump_, scalar(0)); 
-- snip --

I imagine this was put in for stability reasons and perhaps because it is, after all, a fan boundary condition but perhaps there could a minimum allowable pressure instead of zero added? i.e. defaults to zero but, if specified, allows negative jumps?

Mike