Modelling free and impacting underexpanded jet fires

A numerical model for predicting jet fires resulting from high pressure, sonic releases of natural gas is described. The model embodies mathematical descriptions of all the important processes occurring in such fires, and is capable of accurately resolving the near field shock structure which occurs in these flows as well as including a realistic sub-model for flame lift-off height and a novel implementation of the discrete transfer method for calculating thermal radiation fields. The accuracy of the complete model is assessed by simulating a number of free jet fires, and a horizontal jet fire impinging a pressure vessel. Predicted flow and heal transfer fields are compared with available field scale measurements, with good agreement with the data being obtained. (C) British Gas plc 1997.