Abstract
Transitional attack represents a pivotal tactic in modern firefighting, whose efficacy is profoundly contingent upon the impact characteristics of water streams and their subsequent distribution patterns. This study integrates computational fluid dynamics (CFD) simulations with experimental validation to develop a momentum decomposition model for jet impingement on a ceiling. The model analyzes the dominant mechanisms of tangential spread and normal rebound on water distribution and optimizes water application strategies. Theoretical analysis reveals that upon ceiling impact, the normal velocity component of the stream undergoes rapid attenuation, causing the flow to be predominantly governed by tangential diffusion. This phenomenon results in an asymmetrically elliptical ground distribution, characterized by a significant concentration of water volume at the terminus of the diffusion path, while wall boundaries induce further water accumulation. A comparative analysis of the stream impact process and water distribution demonstrates a high degree of concordance between experimental and simulation results, thereby substantiating the reliability of the proposed model. Numerical simulations demonstrate that an increased jet angle markedly improves both coverage area and flux density. Higher water pressure enhances jet kinetic energy, leading to improved distribution uniformity. Appropriately extending the horizontal projection distance of the water jet further contributes to broadening the effective coverage. The parametric combination of a 49° jet angle, water pressure of 0.2–0.25 MPa, and a relative horizontal distance of 1.5–2.0 m is identified as optimal for overall performance. This research provides a scientific foundation and practical operational guidelines for enhancing the efficiency and safety of the transitional attack methodology.