船用喷水推进泵装置水力特性数值模拟

Numerical simulation of performance of marine waterjet propulsion system

为了更好地分析喷水推进导叶式混流泵装置的水力特性,通过选取标准k-ε湍流模型,采用计算流体动力学分析软件CFX对包括推进泵、进水流道、船底水体和喷嘴在内的船用喷水推进装置在各流量工况下的运行情况进行了数值模拟,分别从流道水力损失分布、装置水力性能、轴向力和内流场特性等方面展开分析.模拟结果表明:流道进口断面到方变圆断面段几何形状较为复杂,水力损失占总损失比重最大,特别是小流量工况,该比重超过了90%,但随着流量的增大,该比重会减小,其余各段水力损失的比重则增加;装置在0.50Qd附近进入水力不稳定区,0.76Qd^1.10Qd为装置运行的高效区,喷水推进泵装置受到的轴向力随着流量的增大而减小;在小流量工况下,叶槽内流态较为复杂,展向涡、径向涡和泄漏涡均较为明显,随着流量的增大,这些涡均逐渐缩小直至消失.

To analyse the hydraulic performance of the mixed-flow pump with vaned diffuser in a waterjet propulsion system more accurately,CFX code is used to simulate the steady turbulent flow in the system,which consists of a pump,entry duct,water body below the vessel and nozzle,at various flow rates by means of the standard k- ε turbulence model. The hydraulic loss distribution,hydraulic performance,axial thrust and flow field features are exploited. Because the geometry of entry duct is relatively complex where its rectangular section at the inlet needs to be transformed into a circular one at the outlet,the hydraulic loss takes a maximum proportion in the entry duct,especially at a low flow rate. In that case,the proportion exceeds 90%. However,this proportion reduces with increasing flow rate,and the hydraulic loss proportions in the other components increase accordingly. The system is subject to the hydraulic instability around 0. 50 Qd. The high efficiency zone exists in the range of0. 76 Qdand 1. 10 Qd. The axial thrust generated by the pump diminishes when the flow rate rises. At a small flow rate,the flow pattern in the impeller is complicated,and the spanwise vortex,radial vortex and leakage vortex are evident. Fortunately,these vortices are shrunk until disappear with increasing flow rate.