Numerical investigation into the influence of cubicle positioning in large-scale explosive arena trials

Abstract

In arena blast testing, a common and economical practice employed is to distribute several targets radially around a central charge. However, if these targets are positioned too proximally, reflections and diffractions of blast waves off neighbouring cubicles can affect the nature of expected blast loading. Computational fluid dynamics software has been used through an extensive series of simulations to identify the levels of interference in incident pressure–time histories with and without an obstructing target present. The data were post-processed to identify the Cartesian co-ordinates in which different levels of interference in peak incident overpressure and incident positive phase impulse were achieved. The results indicated that in all cases, there was a greater interference in peak incident overpressure than incident positive phase impulse values directly proximal to the target but, at greater separations, significant differences in incident positive phase impulse existed where peak incident overpressure had returned to free-field equivalent magnitudes. When compared with the established ‘rules of thumb’ for cubicle placement, for targets at different stand-off ranges, an angle of 45° to the rear cubicle still holds some practical relevance, although it is too acute to cover all interference effects. For targets positioned at the same stand-off range, a separation distance of two cubicle widths is generally too conservative and, in many cases, more cubicles can be positioned around the charge. A bespoke recommendation table has been presented for targets at stand-off ranges between 15 and 50 m to allow users to identify the minimum distance from a target at which obstructed-field peak incident overpressure and incident positive phase impulse values differ negligibly from free-field equivalents.