喷水推进泵驼峰区波峰与波谷内流作用机制

Internal Flow Mechanism of the Water jet Pump at Crest and Trough Conditions in the Hump Region

喷水推进泵一般选用轴流泵或导叶式混流泵。高比转速的混流泵和轴流泵在流量-扬程曲线上容易出现驼峰甚至双驼峰,当运行在驼峰区域时,泵和整个系统都可能会出现流动紊乱和振动噪声加剧等问题。在舰船变速航行时,喷水推进泵需要相应地改变转速;在变速过程中,喷水推进泵可能会进入驼峰区域,不利于舰船高效且低噪声地航行,进而影响乘员的舒适度与舰船的隐蔽性,甚至会对推进系统造成破坏。该文研究对象为带导叶的混流式喷水推进泵,基于标准轴(混)流泵试验台和高精度试验测试方法,获得了试验泵的水力性能曲线,试验发现其存在明显的能量特性曲线驼峰现象且伴随振动加剧;根据喷水推进泵试验泵几何模型建立了流体域三维模型,并采用精细化结构化网格划分。研究发现:在波谷工况时,叶轮流域内在展向高度较高位存在明显的低速涡团,不同流道间的低速涡团存在结构和尺度差异;A区域中的流速虽然较低但仍然呈螺旋前进,B区域中流速更低且旋转程度更大,C区域中的流速比A和B区域中稍高。而在波峰工况时,叶轮流域中的流动更均匀且更平顺,在流道中的稳定流动结构明显减少。

Waterjet pumps generally use axial flow pumps or guide vane mixed flow pumps.A hump or even double-hump are often observed in the Capacity-Head(Q-H)curve for the high specific speed mixed flow pumps and axial flow pumps.When the pump is running in the hump region,the pump and the entire system may have problems of flow turbulence and increased vibration and noise.The waterjet pump may enter into the hump region during the rotation change of the waterjet pump corresponding to the ship speed change,which imposes hindrances to the efficient and low-noise operation of the ship,and affects the comfort of the crew and the stealthiness of the ship,even damages the propulsion system.The hydraulic performance curve of a test pump for a mixed-flow waterjet pump with guide vanes is obtained based on the standard test platform of axial(mixed)flow pumps and high-precision test method.It can be observed that there is a significant hump in the energy characteristic curve,accompanied with intensified vibration.A three-dimensional model of the fluid domain has been established according to the geometric model of the test pump for the waterjet pump,being divided by refined structured grids.The results show that under the trough condition,there are significant low-speed vortices in the impeller domain at a higher height in spanwise.The structure and scale of the low-speed vortices between different flow channels are different.In region A,though the flow rate is relatively slow,the flow still moves forward in a spiral.And in region B,the flow rate is even lower but with greater degree of rotation.Although the flow velocity in the A region is lower but still spirals forward.The flow rate in region C is slightly larger than those in region A and region B.However,under the crest condition,the flow in the impeller domain is more uniform and smooth,and the stable flow structure in the flow channel is significantly reduced.