Rapid prediction of fire-induced heat flux on the liners of horseshoe and circular tunnels with longitudinal ventilation at critical velocity

Abstract

A fast-running model is proposed to predict heat flux from enclosed fires on the concrete liners of horseshoe and circular tunnels that have longitudinal ventilation operating at critical velocity. A wind-tilted 3D discretized solid flame transmits radiation to the visible interior surfaces of the tunnel liner. The emissive power of the solid flame is calculated as a fraction of the fire's total heat release rate. If the calculated flame length exceeds the tunnel height, the solid flame shape is shortened (or “confined”), and its emissive power is amplified proportionally to the geometric confinement. Convective heat flux from the combustion byproducts (which are pushed downstream by the longitudinal ventilation) is represented as a zone of semi-empirical decay from the peak heat flux at the tip of the wind-tilted solid flame shape. Spatial predictions of total heat flux from the wind-tilted Confined Discretized Solid Flame (CDSF) model show good agreement with high-fidelity computational fluid dynamic simulations (which are themselves validated against available test data) for fires with heat release rates ranging from 30 to 300 MW in three tunnel prototype cross-sections. Due to its computational efficiency, the wind-tilted CDSF model is conducive to rapid assessment and stochastic evaluation of tunnel liners for thermo-structural fire effects.