Set the pressur to same for both then messure he outlet BC and measure the static pressure. This could be a bit tricky but it should work.
in an internal analysis if you set a pressure on both sides, you're defining the flow rate in the system. if you're using an internal flow simulation fan with a fan curve (vs a rotating region). you're going to see how well that fan works under those conditions.
also, if you're using environmental pressure, remember that defines total pressure at the inlet and static pressure at the outlet, so you'll be generating a pressure difference that is higher than what you're actually expecting. something you might want to do before you move forward too far is just run the pipe without the fan to see how this part works.
if you're using a rotating region because you're designing the fan yourself, i think you'll have to go to an external analysis. i ran an analysis like this recently and the developers agreed that the software wouldn't work well defining environmental pressure on both sides that are exactly the same. or static pressures that are the same.