Wind Forces and the Proximity of Cooling Towers to Each Other

Abstract

Gunn and Malik have recently suggested¹ that their results showing the effect of spacing on the drag of an array of spheres in a closed duct provide an explanation for the collapse of the Ferrybridge cooling towers. It is well known that the drag of a grid of bars or a screen in a wind tunnel increases rapidly as the solidity (that is, the blocked area over the total area) increases. The air passes through the grid as a series of jets and, crudely, it can be argued that the velocity in these jets varies as the solidity. Because aerodynamic forces increase as the square of velocity the drag of the grid will go up as the square of the solidity. For an array of spheres the solidity is , where a is the gap in diameters between adjacent spheres; Gunn and Malik present results for a = 1.0, 0.5 and 0. Using this crude theory, over this range one might expect an increase in drag coefficient based on upstream velocity of some sixteen times.