Unsteady natural ventilation at model scale-Flow reversal and discharge coefficients of a short stack and an orifice

Measurements of unsteady flow rates and pressures have been made on a scale model of a building fitted with two openings-a short stack and a sharp-edged orifice. The flow reversal characteristic of the stack is found to be different to that of a longer stack tested in an earlier study. The short stack displays a greater propensity to reversal, which is consistent with its lower inertia. The time-averaged discharge coefficients of both the stack and the orifice have been examined to determine the effects of external flow. It is found that the effects are similar to those observed in an earlier study that used a different experimental approach.