Modelling fluctuating air flows through building cracks.

The paper summarises an approach to determining the equations governing the air flow through simple cracks subject to fluctuating pressures. To this end, an experimental arrangement has been developed that enables the laboratory simulation of fluctuating driving pressure signals. A standard straight crack was subjected to this signal, which fluctuates in both magnitude and frequency. An air control system permits a high level of fluctuating pressure control. Pressure fluctuations are imposed on a 1m² section of wall with a centrally mounted crack and the overall volumetric air flow rate, pressure distribution and flow direction are monitored. In addition to the experimental testing, computational fluid dynamics (CFD) analyses were carried out for the crack type and specific flow condition. An analysis was made of initial physical test results and a comparison made between these findings and the preliminary CFD models developed. A background to the work is given anct the methods used in simulating the necessary conditions for fluctuating crack flow measurement and the preliminary results of the physical testing and CFD analyses are presented.