The Use of an Unstructured Adaptive Mesh Code to Perform Resolved Obstacle Computations for Confined Explosion Hazards

The establishment of safety cases for oil and gas installations requires accurate estimations of the effects of confined explosions and in particular the over-pressures generated. The shortcomings of the current understanding, traditional semi-empirical methods, and Computational Fluid Dynamic (CFD) techniques have been clearly highlighted in many cases, including the recent SCI full-scale evaluation exercise, where over-pressures were severally underpredicted. Despite this, there is a growing recognition that CFD has an important role to play and a number of different techniques are currently being developed for confined explosions, e.g. see [1-4]. Structured mesh codes can typically handle only about 10 obstacles. Extension of such codes to larger numbers of obstacles is limited by computer resources required to ensure at least 10 cell resolution of the obstacles and more importantly their shear layers [1]. For real installation modules, containing several hundred or even thousands of obstacles, unresolved calculations using Porosity, Distributed Resistance (PDR) models are currently the only CFD option. In this approach obstacles are not resolved, but are represented by resistance terms appended to the mean and turbulent sources, and these methods are limited by the accuracy of these terms, which can only be improved by access to detailed parametric data or high quality resolved computational results. Formulating resistance terms is thus very difficult for complex geometries...