The drag force distribution within regular arrays of cubes and its relation to cross ventilation – Theoretical and experimental analyses

Abstract

A novel set of wind tunnel measurements of the drag force and its spatial distribution along aligned arrays of cubes of height H and planar area index λp (air gap between cubes) equal to 0.028 (5H) to 0.69 (0.2H) is presented and analysed. Two different types of measurements are compared: one type where the drag force is obtained using the standard load cell method, another type where the drag force is estimated by measuring the pressure difference between windward and the leeward façades. Results show that the drag force is nearly uniformly distributed for lower λp (0.028 and 0.0625), it decreases up to 50% at the second row for λp = 0.11, and it sharply decreases for larger λp (from 0.25 to 0.69) where the force mostly acts on the first row. It follows that for the lowest λp the drag force typically formulated as a drag area corresponds to the total frontal area of the array, whereas for large λp the drag area corresponds to the area of the first row. By assessing the driving pressure for ventilation from the drag force, the analysis is extended to estimate the cross ventilation as an example of application of this type of measurements.