Experimental and theoretical analysis of crosswind effects on the evolution of down-reaching flame behaviors in heptane tank fires

Tank fires pose significant threats to industrial safety and environmental protection in liquid energy storage systems. The geometric characteristics of flames in such fires, influenced by factors like crosswind and ullage height (h), are crucial for assessing heat flux, establishing safety distances, and designing firefighting strategies. This study is aimed at investigating the coupled effects of crosswind and ullage height on the flame behaviors of tank fires. Key geometric parameters of the down-reaching flames, including the retraction length (L _U), back-dragging length (L _D), down-reaching depth (H _D), and tilt degree (α) are analyzed. Experimental results reveal two distinct flame behaviors during the stable burning phase: (i) when the ullage height is small (h<0.8D), the flame is in contact with the tank bottom and both L _U and the L _D decrease with an increase in either crosswind speed or ullage height, and (ii) when the ullage height is large ((h≥0.8D), the flame detaches from the tank bottom and H _D increases with both crosswind speed and ullage height due to increased negative pressure in the downwind side of the tank. Based on theoretical analysis and experimental data, predictive models are developed for H _D (non-bottom-contacting mode) and L _D (bottom-contacting mode). These findings can offer insights into the safer design of tank installations and provide guidance for effective firefighting strategies.