Modeling the inside defect of the jet cavitator

Introduction. The investigation of the hydrodynamic cavitator operation used under the erosion impact on a solid body surface, and of the device structure optimization for increasing the damage capability of the cavitating jet is presented. The effect of a sporadic defect of the combined nozzle inside on the volume fraction of the vapor content and the cavitation region geometry is considered. The work objective is to identify the influence pattern of the inside defect of cavitators of various sizes on the hydrodynamic and cavitational characteristics of the nozzle through numerical modeling. Materials and Methods. The features of the ANSYS Workbench finite-element analysis software package and the integrated optimization module of the development and design process in the domain of the computational fluid dynamics ANSYS CFX are used. The simulation is based on the experimental data obtained under the nozzle water discharge at a specially designed laboratory bench under the cavitation condition. Research Results. Graphic dependences of the volume fraction of the vapor content, total pressure and the length of the cavitation region on the distance along the axis of the jet for different defect sizes are obtained and presented. Two phases of the cavitating jet flow in a nonideal cavitator are identified, and the transition effect on the velocity distribution in the device section is shown. Discussion and Conclusions. The occurrence of an internal defect on the surface of the conical pattern of a combined nozzle with the size of less than a quarter-diameter of the central cylindrical portion may not cause visual changes in the cavitation region geometry, but it significantly reduces the erosive capacity of the cavitation jet. A further defect increase results in a total suppression of the cavitation flow, but maintains its dynamic behavior. The obtained results contribute to the improvement of the hydrodynamic cavitators design, to the enhancement of their erosive impact with the use of cavitation for cleaning underwater structures and mechanisms.