# Analysis of Flow Field Characteristics in the Three-Phase Jet Fire Monitor Head
## 1 Introduction
[14] took self-operated water jet nozzles as the research object and adopted a k-\(\epsilon\) turbulence model based on Fluent to simulate nozzle jets with different nozzle sizes and arrangements in the pipeline, and compared the distribution of jet flow field and the changes in velocity and displacement of nozzles with different parameters in the pipeline. These studies indicate that different nozzle and fire monitor structures can significantly affect the internal flow characteristics, with improved nozzle structures effectively enhancing jet performance. In closed fluid domains, straighteners, as crucial components of the IFF structure, can significantly influence flow characteristics. [PERSON] et al. [15] performed multi-objective optimization on straighteners in large fire monitors' IFFs using CFD simulations to maximize flow uniformity and minimize pressure loss. The optimized rectifier design significantly improved flow uniformity and reduced pressure loss. [PERSON] et al. [16] studied the effects of various IFF structures, such as different curvature radius bends, guide plates or straighteners, and the position and number of guide vanes, on the flow characteristics of fire monitors, finding that IFF structures have a significant role in eliminating vortices and achieving constant flow. Eliminating vortices and crossflows within the pipe can effectively increase the range of the fire monitor. [PERSON] et al. [17] found that in HVAC systems' square ducts, reducing the hydraulic diameter of the flow straightener decreased turbulence intensity, which helps achieve uniform airflow distribution. In addition, [PERSON] et al. [18] found in the study of the vortex pump that optimizing the length of the inclined blade in the internal flow passage can effectively reduce the gradient of velocity, reduce the cavitation phenomenon, and improve the flow characteristics of the IFF. A reasonable combination of straightener structure and suitable IFF mechanisms can effectively reduce turbulent kinetic energy (TKE) within the pipe, improve outlet velocity uniformity, and enhance flow characteristics. The volume of fluid (VOF) method proposed by [PERSON] et al. [19] has been widely used for dynamic simulations of free boundaries. This method accurately simulates interface behavior in multiphase flows by tracking fluid interface changes. The VOF method plays a crucial role in analyzing the IFF characteristics of fire monitors, improving simulation accuracy by precisely modeling the interface behavior between liquids and gases during jetting. [PERSON] et al. [20] used the VOF method to study the impact of geometric variations on nozzle internal flow, conducting three-dimensional steady-state incompressible turbulent flow analysis on five different nozzle geometries, and found significant effects were produced by geometric changes on the flow patterns and nozzle outlet velocity distribution. [PERSON] et al. [21] adopted the Euler-VOF model, a CFD simulation method, to solve the air-water multiphase flow in the abrasive water jet. Due to the invisibility of internal fluid dynamics, analyzing the IFF of fire monitors is limited. The VOF method effectively addresses invisibility issues, maximally restoring flow states and providing insights into fluid characteristics. Research on the TPJFM is scarce. [PERSON] [22] designed a TPJFM and individually optimized its main structural parameters, resulting in an optimal set of parameters. However, this study only considered the influence of parameters on jet performance without analyzing the flow characteristics within the IFF. Further analysis is needed to understand the impact of specific structural parameter changes on flow characteristics. [PERSON] et al. [23] studied the nozzle of a TPJFM, combining the Kriging surrogate model with NSGA-II for multi-objective optimization of the main structural parameters of the nozzle's IFF. The results showed that the optimized nozzle's IFF reduced the inlet and outlet pressure drop (PD) by 3.48%, and the average TKE at the outlet decreased by 29.38%.