喷水推进器失速工况下流动及压力脉动特性

The Flow and Pressure Pulsation Characteristics of Water-Jet Propulsion under Stall Condition

摘要: 处在小流量工况下运行的喷水推进泵，由于进口来流冲角的增大，会在叶片背部发生脱流，从而引发内部的不稳定流动。为了探究这种流动特性，建立了一个完整的三维喷水推进系统模型，包括进水管道、推进泵和喷管。本文采用计算流体力学方法(CFD)，并基于SST k-ω湍流模型，对喷水推进泵在多种工况下的内部流场展开数值计算研究。结果表明：随着流量的减少，推进泵的扬程和效率曲线均出现大幅度的下降，呈现具有正斜率的驼峰特性；设计工况下推进泵内部流动稳定，随时间变化较小；临界失速工况下导叶内部涡核形状随着时间不断变化；深度失速工况下推进泵内部速度和压力变得紊乱；在压力脉动方面，设计工况下推进泵内各位置的压力脉动主频均为叶频；从叶轮进口到导叶出口，叶轮通过频率的主导作用依次减弱，压力脉动幅值逐渐降低；失速工况下各位置的压力脉动幅值较设计工况均有所增加，脉动频谱变得混乱并伴随有低频特征的出现。

Abstract: Water-jet propulsion operating at low flow rates may cause flow separation at the back of the blades due to the increase of angle of attack of the inflow. This can lead to internal unstable flow. In order to investigate the flow characteristics, a complete 3D waterjet propulsion system model, including inlet pipe, impeller, and nozzle, was established. Computational fluid dynamics (CFD) with the SST k-ω turbulence model was used to numerically simulate the internal flow field of the waterjet pro-pulsion under various operating conditions. The results showed that with decreasing flow rate, the head and efficiency curves of the impeller decrease significantly, showing a tent- shaped slope. At the design operating condition, the internal flow of the impeller is stable and changes little over time. In the critical stall condition, the vortex core shape inside the guide vanes changes continu-ously over time. In the deep stall condition, the internal velocity and pressure of the impeller be-come chaotic. Regarding pressure pulsation, the main frequency of pressure pulsation at all posi-tions inside the impeller is blade frequency at the design operating condition. From the inlet of the impeller to the outlet of the guide vanes, the dominant effect of the blade passing frequency gradu-ally weakens, and the amplitude of pressure pulsation gradually decreases. The amplitude of pres-sure pulsation at all positions under stall conditions is higher than that under design conditions, and the pulsation spectrum becomes chaotic and with low-frequency characteristics.