Experimental study of crack flow with varying pressure differentials.

Existing experimental techniques for calculating air flow through building cracks are usually based upon relationships derived from experimental studies employing relatively simple procedures. Typically, a fixed pressure difference, dP, is established across the crack of interest and then the air flow Q through the crack is determined. Most crack flow equations take the pressure differential dP to be steady-state. In reality, the wind forces which generate much of the driving pressures represent highly fluctuating signals. A basic problem is to know what effect a fluctuating dP has on the overall air flow through building cracks. The basic aim of this study was to determine the impact of these fluctuating pressures on crack flow equations. Experimental techniques generated sinusoidal pressure fluctuations across a range of fabricated, straight-through cracks, ranging from 1 to 5 mm in thickness. Fluctuation frequencies from 0.5 to 2.5 Hz were used in the investigations. The results suggest that the average flow under conditions of fluctuating pressure differentials does not differ significantly from the flow which would occur if the mean pressure differential were imposed. This implies that the instantaneous flow at any fluctuating value of the pressure differential is that corresponding to the pressure differential on the steady-state flow-pressure curve.