液固两相离心泵内固体颗粒对液相湍流调制的测试方法及机理

PIV test methods and mechanism on liquid turbulence modulation by solid-particles inside a centrifugal pump

固液两相离心泵的性能和效率受控于泵内的两相流动规律,理解泵内的两相流动规律和磨蚀机理,对于合理设计和延长泵的使用寿命具有重要意义.以离心泵内的固液两相流为研究对象,通过搭建无搅拌固液两相流PIV测试平台,消除高速搅拌对泵内流场的影响,改进颗粒-流体的两相循环方式,提高了实验的测试精度;通过POD方法分析低固相浓度时泵的性能改善的原因,探寻固体颗粒对泵内液相湍流的调制机理.进一步补充和完善固液两相流水动力学理论体系,为指导固液两相流高效的工业应用提供理论基础.

As one of high energy consumption pumps, pump used for solid-liquid two-phase mixture transportation, such as slurry pump and mud pump, is extensively used in the hydraulic transportation of solid-liquid mixture through pipes in various fields. The erosion wear in slurry pumps has been identified as a critical issue during transportation of slurry as it affects the equipment performance and reduces its reliability and operation life, leading to the waste of energy. Many studies indicate that the performance and efficiency of solid-liquid two-phase centrifugal pump is controlled by the two-phase flow pattern inside the pump, so understanding flow characteristics and abrasion mechanism has important significance to improve the hydraulic design of the impeller for decreasing the abrasion and increasing the service life of the pump. In the present study, based on solid-liquid two-phase flow as object, an improved experimental facility without agitation was developed can improve the test precision by eliminating the influence of agitation on flow inside pump and improving particle-liquid two-phase flow circulation way. On the base of experimental studies, POD methods were applied to analysis the liquid turbulence modulation by solid-particles and the behavior of large eddy structures will be clearly understood. Thus, the theoretical system of the solid-liquid two-phase flow will be further improved. And a theoretical principle for the solid-liquid two-phase pump optimal design will be presented. The following conclusions are obtained：（ⅰ） a superior PIV two-phase test platform than that in the previous literature is designed and it can be very good to realize a stable solid-liquid two-phase flow measurement of centrifugal pump. Compared with the traditional platform, the results obtained by the novel solid-liquid two-phase centrifugal pump PIV test platform has a very high accuracy and it has a good reference value to understand flow mechanism of a centrifugal slurry pump. The two particle images with and without agitating are shown in Figure 5. As can be seen that a large number of bubbles are brought into the circulation line（Figure 5（a））, which is caused by a higher stirring speed for suspending solid particles, and thus the actual flow images shows a gas-liquid-solid three-phase flow. However, for the present test facility without stirring, there is no such problem, and the original image is very clear without bubbles.（ⅱ） The POD analyses show that the solid-particles injection has an important influence on the large scale turbulence structures which contain a large amount of energy. The modal energy distribution as a function of the POD mode number is displayed in Figure 10. The energy contribution of these large scale structures to the total energy becomes larger due to the injection of solid-particles, whereas the contribution of the small scale structures, which denotes the energy dissipation, becomes smaller. This is why the low solid-phase volume concentration has higher pump head and efficiency. The addition of solid-particle increases the friction loss, but reduces the flow separation loss and inhibits the development of small scale vortex. However, with the increase of solid-particle concentration, the friction loss increases is greater than the flow separation loss reduction, and thus pump head and efficiency decrease. The above phenomena show fully that the solid-particles addition has an important influence on the large scale energetic eddy structures. This is confirmed by the measurement results as shown in Figure 11.