Розробка моделі руху водного струменя після виходу з пожежного ствола

This study investigates the process of water jet motion in the air; the subject is the trajectory of motion and the velocity vector of water droplets in a two-phase "droplets-air" flow. The task addressed is to construct a model of water jet motion in the air, which would take into account its destruction and transformation into a stream of droplets. A model of water jet motion in the field of gravity after exiting the fire hydrant in the area of the jet core has been built. The jet expansion coefficient was experimentally determined to be 0.016. Estimates of the jet radius, water droplet velocity, and effective radius of the jet of trapped air at the boundary of the core zone and the droplet zone were constructed. The values obtained are the initial conditions for the model of the motion of the droplet and gas phases of the jet in the droplet zone. The droplet motion was modeled by using the Lagrangian approach, within which the dynamics of the motion of individual drops were considered, described by the equations of motion in three-dimensional space taking into account the forces of aerodynamic resistance and gravity. It was assumed that the distribution of the droplet diameter obeys the Rosin-Ramler law. A model of the motion of the gas phase of the jet was constructed, based on the equations of mass and momentum balance; it also takes into account the curvature of the jet axis due to the capture of air by drops moving under the action of gravity. The model is based on the assumption of the axisymmetric nature of the jet and the Gaussian velocity distribution in its cross section. A feature of the model is the mutual influence of the droplet and gas phases of the jet on the motion of each other: drops, losing momentum due to aerodynamic resistance, give it to the air. It is shown that drops of smaller diameter have a shorter range compared to drops of larger diameter. As a result, the water falls to the ground not at a specific point but in a certain range. In particular, for a fire hose with a diameter of 19 mm, a delivery angle of 35° to the horizon and a water pressure of (40÷70) m, the width of the range into which 90% of the water falls was (8.7÷11.0) m