The Influence of Internal Geometry on Pressure Losses, Hydraulic Stability, and Cavitation Risk in a Firefighting Monitor

Abstract

This paper presents a combined CFD and experimental investigation of water flow through a Shootfire-1000 water-foam fire monitor. The study aimed to assess pressure losses, flow characteristics, hydraulic stability, and cavitation risk, and to evaluate the influence of selected geometric and operating parameters on hydraulic performance. A numerical model based on the actual geometry of the device was developed and experimentally validated using pressure loss measurements obtained under representative operating conditions. The influence of flow rate, monitor elevation angle, water temperature, nozzle cone position, and cone plate fillet radius was analyzed. The results showed that the dominant pressure losses occur within the monitor head, particularly in the annular constriction formed by the nozzle cone and the housing. Water temperature and monitor elevation angle had only a minor effect on the overall hydraulic performance, whereas relatively small modifications of the nozzle cone geometry significantly affected pressure losses. The analyses further demonstrated that local geometric features play a key role in determining velocity distribution and hydraulic stability. No pressure values below the water vapour pressure were observed within the investigated operating range, indicating a negligible risk of cavitation. The results confirm that optimization of the monitor head geometry can effectively reduce hydraulic losses and improve the hydraulic performance of water-foam fire monitors.