Numerical simulation of cavitation characteristics in high speed water entry of head-jetting underwater vehicle

头部喷气航行器高速入水空泡特性数值分析

¹ School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China
² Key Laboratory of Unmanned Underwater Vehicle Technology of Ministry of Industry and Information Technology, Xi’an 710072, China

Received: 20 October 2020

Abstract

Autonomous underwater vehicle will be subjected to a huge impact load during high speed water entry, which will damage the structure and the internal instruments of the vehicle. Therefore, it is of great significance to study the buffer mechanism of the vehicle during the process of water-entry. In this paper, a kind of head-jetting device with disk cavitation is used. The complex cavitation forms, under the three-phase coupling of gas, liquid and solid, in the water entry process of the vehicle on which the device is installed. In this paper, the numerical simulation of high-speed water entry of the vehicle equipped with head jet device is carried out. Through the analysis of water entry cavitation under typical working conditions, the following conclusions are obtained. After the installation of head jet device, the water entry cavity of the vehicle changes gradually from cone to spindle shape. The air jet, compared with that without jet, can promote the formation of water inlet supercavitation, decrease the interaction area between the vehicle and water, and reduce the impact load during water entry. At the same water entry depth, the diameter of cavitation increases with the amount of air jet. The water entry velocity has a great influence on the difference of cavitation shape. The water entry depth closure phenomenon, when the water entry velocity is less than 100 m/s, can be observed in the depth of 3.5 times of the projectile length. The water entry angle has a significant effect on the cavitation shape. The cavity shows obvious asymmetry when the vehicle slants into the water, and the diameter and length of the bubbles decrease with the increase of the water entry angle. The research content of this paper provides technical support for the engineering practice of high-speed water entry and load reduction, and the conclusions are of great significance in related fields.

摘要

航行器在高速入水的过程中会受到巨大的冲击载荷作用，它会破坏航行器结构并损坏内部仪器，因此开展航行器入水缓冲机理的研究是很有意义的。使用一种带圆盘空化器的头部喷气装置，在气液固三相耦合下，航行器入水过程产生了复杂的空泡形态。开展了加装头部喷气装置的航行器高速入水数值模拟研究，通过对典型工况下入水空泡的分析，得到如下结论：加装头部喷气装置后航行器入水空泡由锥形逐渐变化为纺锤形；与不喷气时相比，喷气可促进入水超空泡的生成，减小入水过程中航行器与水的作用面积，降低该过程中的冲击载荷；同一入水深度下，空泡直径随喷气量而增大。入水速度对空泡形态差异性影响较大，其中入水速度100 m/s以下时可在3.5倍弹长的入水深度内观察到入水深闭合现象。入水角对空泡形态有明显影响，斜入水时空泡呈现明显不对称性，且空泡直径与长度随入水角增大而减小。研究内容为航行器高速入水降载的工程实际提供了技术支持，所得结论在相关领域具有重要意义。