A Simple Approximation to Predict the Transition from a Balcony Spill Plume to an Axisymmetric Plume

Abstract

All existing simple entrainment calculation methods for the three-dimensional (3D) balcony spill plume assume that the mass flow rate of gases produced increases linearly with height of rise. It is recognized that at very large heights of rise the balcony spill plume will eventually behave like an axisymmetric plume in terms of entrainment behavior. The transition from a balcony spill plume to axisymmetric has not been rigorously studied and current guidance can only be considered to be an estimate. To remedy this situation, a general approach similar to that used in previous work is utilized to develop a simple approximation that predicts the height of transition in entrainment behavior. This type of analysis is further supported with a limited number of simulations using numerical modeling. The proposed simple approximation provides an upper height limit for which linearly based 3D balcony spill plume entrainment formulae can successfully be applied.