Many years ago I took part in an experiment on a VC10 to see whether opening a DV window would help remove smoke from the cockpit. We depressurised the aircraft, flew straight and level at (as I remember) around 5000ft and 230 kts. A smoke cannister was activated in the rear of the cockpit and each pilot in turn opened their DV windows (one at a time).
There were two effects:- (1) the stream of smoke came forward from the rear of the cockpit and then flowed across the instrument panel towards the open window reducing even further the visibility of the instruments on that side; (2) the noise was so great that conversation was almost impossible and we had to revert to hand signals.
I am sure that the aerodynamics of different aircraft would produce slightly dfferent results. But I would hesitate to open a cockpit window or hatch, if only for the reason that the noise renders normal cew coordination extremely difficult.