A computational fluid dynamics model is established to investigate the behavior of fire smoke spreading in L-shaped utility tunnels with small curvature radii (R). The fire evolution process for tunnels with R = 0–25 m and critical ventilation velocities (V) of 0.5–3.0 m/s is analyzed, and the Richardson number (R_i) is introduced to determine the critical value for the development of fire smoke back-layering. The results show that R and V strongly influence the fire-induced spatiotemporal evolution characteristics in such utility tunnels. Smaller R or higher V are associated with stronger centrifugal forces, which causes the smoke to move downstream of the fire source and increases the instability and risk. The non-dimensional smoke back-layering length shows a linear relationship with ln(Q*/V*³), where Q* is the dimensionless fire source power. Integrated with the V and smoke force in a curved tunnel, the critical R_i value is found to be 6.34 for R = 10 m. This means that smoke back-layering will appear when R_i > 6.34 and disappear when R_i < 6.34. The present work positively provides a tool for the assessment of thermal environment of L-shaped utility tunnel's fire safety in engineering practice.

建立了计算流体动力学模型，以研究火灾烟雾在小曲率半径（R）L 形综合管廊中的扩散行为。分析了R  =0~25 m、临界通风速度（V）为0.5~3.0 m/s的隧道火灾演变过程，并引入理查森数（R _i）确定火灾发展的临界值烟背分层。结果表明，R和V强烈影响此类综合管廊火灾引起的时空演化特征。较小的R或较高的V与更强的离心力有关，这会导致烟雾向火源下游移动并增加不稳定性和风险。无量纲烟背层长度与ln( Q */ V * ³ )呈线性关系，其中Q *为无量纲火源功率。结合弯曲隧道中的V和烟雾力，发现临界R _i值对于R  = 10 m为 6.34 。这意味着，抽烟背分层时会出现ř_我 > 6.34和消失时ř_我 < 6.34。本工作为工程实践中L型综合管廊消防安全热环境评价提供了积极的工具。