非均匀进流下喷水推进泵的内流特性和载荷分布

Flow Feature and Blade Loading of a Water-Jet Pump under Non-Uniform Suction Flow

关键词:  非均匀进流  周向畸变  喷水推进泵  内流特性  叶片载荷  分离涡

Key words:  Non-uniform inflow  Circumference distortion  Water-jet pump  Flow feature  Blade loading  Separation vortex

摘要:

为描述实际航行时喷水推进泵非均匀进流的结构特点，解释喷水推进泵实际性能与试验测试值之间的差异，采用雷诺时均模型和RNG k-ε湍流模型数值计算非均匀进流下喷水推进泵的外特性，对比后获得了非均匀进流下喷水推进泵外特性降幅曲线，其中扬程和效率的最大降幅均为30%。进一步求解内流场，结果表明:非均匀进流中的低能螺旋流受旋转叶片的诱导，在轮缘处演变为以周向分离涡为主的进口畸变流，流道堵塞，受排挤的工作流体因液流角过大在叶片轮毂处发生流动分离，最终卷吸形成螺旋分离涡；此分离涡沿径向扰动叶片前缘流场，诱发回流和二次流，加剧了水力损失。同时，分离涡破坏绕翼环流，改变叶片静压分布，导致叶片载荷由前载型转变为中载型，削弱了叶片做功能力。因此，内流特性和载荷突变共同证实了非均匀进流是喷水推进泵性能下降的主要原因。

Abstract:

Insufficient understanding of large deviations between experiment performance and actual performance is a major problem encountered in the water-jet pump application. This study describes the non-uniform flow structure from the intake duct，and explains the physical mechanism and blade loading for deviations. The description and explanation are based on numerical simulations by means of RANS and RNG k-ε Model，corroborated by experiments. As a result，the non-uniform inflow has been proved as a major factor to weaken a water-jet pump，according to the blockage of an inlet distortion upstream the blade shroud and the considerable disturbance of a hub separation vortex. In detail，the inlet distortion is actually a circumferential separation vortex revolution from the lower energy flow of the non-uniform suction flow. The lower the attack angle，the higher the pattern of separation flow with consequent a spiral focus-type vortex on the pressure side of blade hub. Then，the crossflow gives rise to radial shedding of the separation vortex and the consequent formation of secondary flow and reverse flow. Meanwhile，the separation vortex reduces the bound vortex of the hub，with a drop of the lift owing to a mid-loaded distribution instead of the fore. Eventually，the separation，vortexes formation and propagation successively，explain the flow mechanism of the non-uniform inflow and the reduction of performance，maximum is 30%.