Abstract The development of oil and gas resources towards the deep sea is an inevitable trend in international energy development. Due to its advantages of high production and transportation efficiency, good flow safety and low investment cost, oil and gas mixed transportation technology has become the preferred technology for deep-sea oil and gas production and transportation system. The core device of the oil-gas mixed transportation system is the gas-liquid two-phase flow pump. Under the gas-liquid two-phase condition, the pressure surging will occur with the increase of the inlet gas volume fraction (IGVF) in the pump. At this time, the pressurization capacity of the pump decreases significantly, accompanied by violent vibration, resulting in extremely unstable operation. To solve this problem, the numerical simulation and experiment of the two-phase operation characteristics of a centrifugal pump and a semi-open mixed-flow pump were carried out in this study. The influence of operating parameters on its pressurization capacity was clarified, and the internal gas-liquid distribution was visually tested, revealing the distribution and its spatiotemporal evolution of gas-phase in the impeller. Finally, the unsteady characteristics of pressure surging were analyzed in detail.

Abstract In order to reduce the flow loss in the volute and improve the efficiency of the centrifugal fan further, a new type volute with a diffusion profile was designed and optimized. The effects of diffusion angles were clarified by using numerical simulations and the method of design of experiment. The mechanism of vortex loss reduction of the diffusion-type volute was revealed. The results show that diffusion-type volute can reduce the flow loss in the volute by 30.8% compared with the original volute, and increase the efficiency of the fan by 2.24%. Parametric studies show that the diffusion angle of front disc has a great influence on the efficiency of the fan, and the effect of diffusion angle of rear disc is relatively less. Mechanism analysis shows that the diffusion-type volute can greatly reduce the vortex strength in the volute, especially eliminate the high-intensity vortex near the volute tongue. As a result, the volute loss is remarkably reduced. In addition, the diffusion-type volute can effectively reduce the amplitude of pressure fluctuation in terms of shaft frequency, characteristic frequency and broadband signals in the volute.

探究泡状入流条件下旋流泵流场演化机理和能量转换特性,对优化旋流泵结构和提升其气液混输性能具有重要意义.采用混合多相流模型与种群平衡模型进行耦合计算了旋流泵气液两相流场,结合能量梯度理论、熵产分析与流场演化规律,获得了泡状入流条件下旋流泵的能量转换特性.结果表明,循环流在无叶腔内呈涡带分布,其中涡室附近的循环流强度较高,涡带分布范围广且结构稳定,而无叶腔小半径处的循环流涡带强度较弱,仅存在于部分流道.随着入口体积含气率的增加,无叶腔内涡团面积逐渐增大,涡核数量有所增加.但当入口体积含气率增加到10%后,继续提高含气率,则循环流数量没有明显变化.在高入口体积含气率下,气相在后缩腔叶轮内聚集,使得后缩腔与无叶腔外缘能量梯度函数值增大,脉动熵产损失提高,流场更加紊乱,旋流泵效率与压差下降.

This work experimentally studied the influence of gas and liquid distribution on a semi-open mixed-flow pump performance. High speed photography technology was contributed to obtain the evolution law of bubbles in the impeller. The results show that the inlet gas volume fraction (IGVF) and liquid flow rate are the main factors affecting the performance of the pump. The pressurization capacity linearly decreases with the increase in IGVF when the liquid flow rate is close the best efficiency point. However, this factor suddenly drops when the IGVF reaches a certain critical value under the condition of a low liquid flow rate. The spatiotemporal evolution characteristics of the isolated bubbles and gas column in the segregated flow were investigated. In addition, the bubbles are evenly distributed, and the flow pattern is mainly bubbly flow (BF) or aggregated BF (ABF) in the impeller inlet area without blades. Under small liquid flow rate conditions, the bubbles tend to coalesce into larger-sized gas-pocket with an increase in IGVF. The tip leakage vortex increases the turbulence intensity of the flow field. The results show that the bubbles downstream of the tip leakage vortex in the impeller channels are more easily broken into smaller bubbles and form a BF or ABF.

Inlet pipes of the centrifugal pump are generally bent to fit in the limited installation space, which can cause inflow distortions for two sides of the double-suction impeller. This study aimed to understand the effect of primary geometric parameters of inlet pipes, including corner angle, straight pipe length downstream of elbow, and turning radius, on pump performance and pressure fluctuations. The pump head, efficiency, and pressure fluctuations were measured for six kinds of inlet pipes in the experiment. Unsteady numerical simulations were performed to understand the flow mechanisms. Results indicate that the bending of inlet pipes is a significant reason for the loss of pump head and efficiency. The penalty on pump performance is augmented by the increase in corner angle, decrease in turning radius, and installation of a short straight pipe downstream of the elbow. Pump efficiency could be maximally reduced by 6.58% with a large corner angle and a small turning radius. The bending of inlet pipes induces pressure imbalance for the two sides of the impeller and increases low-frequency disturbance in the suction chamber, which are responsible for the performance loss. Numerical results reveal that the low-frequency disturbance is caused by the vortex formed in the suction chamber, and the accompanying secondary vortex aggravates the pressure fluctuation synchronously. Parametric studies conclude that the corner angle should be minimized to reduce the penalty on pump performance and pressure fluctuations, and a long straight pipe downstream of the elbow can be installed to decrease vibration for the pump with bent inlet pipes.

转轮的径向振动特性对水轮机转子系统的稳定性至关重要.为了研究空化对轴流式水轮机转轮径向振动特性的影响规律,本文首先搭建了包含激光测振仪(Laser Doppler Vibrometer,LDV)的非接触式振动测试系统,并结合高速摄影系统获得了不同空化状态下的转轮内部流场图像以及转轮径向振动信号.然后对转轮内部流动图像及振动信号进行了综合分析,结果表明:从无空化到空化初生阶段,空化系数的降低对转轮径向振动基本没有影响;空化初生以后,转轮径向振动的幅值会随着空化程度的加剧而急剧上升.转轮内部空化流动形态的转变是转轮径向振动频域特性改变的根源.从空化初生到完全空化阶段,转轮径向振动的能量会出现向低频区域迁移的趋势,增加机组共振的风险.本文的研究对轴流式水轮机稳定运行以及经济性具有重要意义.

该文以某多级气液混输泵为研究对象,采用混合模型进行数值模拟计算,探究了在4种不同进口含气率条件下,含空间导叶扩压器内部的复杂流动.结果表明:在不同进口含气率条件下,混输泵扩压器各流道内均产生了不同程度的通道涡,导致气体在扩压器导叶背面涡核中心附近聚集,从而降低了混输泵的运行效率.通过非定常数值模拟分析发现,随着进口含气率的增大,概率密度函数峰值不断减小,而低频段的压力脉动幅值逐渐变大.扩压器的轴向振动幅值远大于相同条件下径向振动幅值,且系统各方向的低频振动幅值均随着进口含气率的增大而增大,并在转轮叶频处振动幅值最大.分析结果显示:在气液两相流条件下,该混输泵扩压器各流道内产生的通道涡及气体聚集是导致扩压器内不稳定流动的关键原因;在低进口含气率条件下,系统主要表现为相对更加集中的脉动能量;扩压器内部不稳定流动及转轮转动是诱发系统振动的主要原因,且主要表现为轴向振动.

为研究侧边机组故障对泵站前池流态的影响,本文建立了某泵站引渠、前池、进水池与吸入管三维数值模型,并基于VOF模型开展了数值计算.然后,根据计算结果分析了不同侧边机组故障情况对前池和引渠内流态的影响.最后,引入了流速分布均匀度作为量化指标,阐述了不同侧边机组故障情况对中间机组的吸入管进口流速分布的影响规律.结果 表明:侧边单台机组故障时,前池内部流速分布相对无故障变化较小,但故障机组吸水池内产生大尺度漩涡,进而导致前池出口断面流速畸变,发生流速掺混现象;侧边机组全部故障时,前池内部产生大尺度涡系,造成前池出口断面流速严重掺混现象,且范围更大,并显著影响中间机组吸入管进口流态,造成进口流速不均匀分布,进而对中间机组运行产生不利影响.

为了探索在不同转速下均可有效提高压气机失速裕度的扩稳方法,以跨声速压气机为研究对象,利用缝式机匣处理和叶顶喷气进行耦合设计,并参数化研究了缝数目、缝长、缝宽及喷嘴周向宽度对压气机性能的影响规律,结合非定常数值模拟揭示了耦合型机匣处理的扩稳机理.研究结果表明,在100％、80％、60％转速下,压气机失速裕度分别提高9.31％、8.26％、8.68％,设计点效率分别降低0.77％、0.23％、0.41％.缝数目、缝长、缝宽是影响压气机失速裕度及效率的显著因素,而喷嘴周向宽度对压气机失速裕度及效率的影响较小.耦合型机匣处理内形成了抽吸、喷气的耦合流动循环,耦合强度的增加有利于压气机失速裕度的提高,但会降低压气机效率.耦合型机匣处理提高了叶顶负荷,但降低了叶顶泄漏强度,极大消除了叶顶泄漏涡引起的叶顶堵塞,这是压气机失速裕度提高的主要原因.耦合型机匣处理具有在不同转速下均能有效扩稳的潜力.

A local-regional power loss analysis method based on multiphase computational fluid dynamics (CFD) simulation results is proposed in this study. This method is used to investigate the energy conversion characteristics of a three-stage electric submersible pump under high inlet gas volume fraction (IGVF) conditions. Results show that the input power and effective power increase first and then decrease along the streamline. When IGVF increases from 0% to 14.5%, the total input power and total effective power decrease by 32.4% and 56.2%, respectively. In particular, the input power and effective power in R4 drop by 62% and 67%, respectively. The high gas volume fraction (GVF) area on the blade pressure surface near the impeller inlet causes the power decrease in R4. However, the input power in R6 increases by 47.5%. This condition is due to a jet flow near the impeller outlet causes the vortex and high GVF area in R6, thereby leading to a high liquid velocity area along the radial direction near the pressure surface of the impeller blade. The kinetic energy of the fluid in the jet region increases rapidly in accordance with Bernoulli equation and is converted into pressure energy in the vortex area. The total power loss increases quickly with IGVF. The power loss near the impeller outlet area at 14.5% IGVF is ten times higher than that of 0% IGVF condition and five times higher than that of 5% IGVF condition. This condition is caused by the large air pockets accompanied by vortices in the area. This work provides a theoretical basis for the design and optimization of the multiphase pump.

为了探索可有效抑制轴流泵特性曲线驼峰区的方法,该研究针对某轴流泵开展端壁沿轴向开缝的数值模拟研究,分析缝数目、缝长度和缝角度对轴流泵性能的影响规律,结合全通道非定常模拟揭示端壁开缝对轴流泵驼峰区的改善机理.研究结果表明,端壁开缝能够有效抑制轴流泵的驼峰现象,失速工况的扬程和效率分别提高了83.5％和8.13％.增加缝的数目和缝长可提高开缝抑制驼峰的能力,但缝过长会降低设计工况的效率,在一定范围内增加缝的径向倾角有利于驼峰区的改善,但不宜超过45°.在驼峰工况区,叶顶泄漏流呈旋涡状向叶轮进口方向发展,与来流共同作用堵塞叶顶通道,导致叶顶区域扬程突降.在叶片正背面压差作用下,缝内建立的喷射与抽吸的流动循环可使相对液流角在0.9倍相对叶高处以上部分明显降低,最大降幅62°,平均泄漏强度降低41.4％,叶顶中部附面层厚度降低18 mm,有效抑制由叶顶泄漏涡与主流相互作用造成的堵塞,并可削弱叶顶部位由叶顶泄漏涡等二次流诱发的压力脉动,是改善轴流泵驼峰区以及提升小流量工况效率的原因.端壁开缝具有改善轴流泵驼峰的巨大潜力.

In order to study the influence of inlet gas volume fraction (IGVF) on performance of a gas-liquid centrifugal pump, three-dimensional turbulent flow of a single-stage gas-liquid centrifugal pump has been simulated by using computational fluid dynamics (CFD). Both steady and unsteady simulations have been conducted for different inlet gas volume fraction conditions of the pump. The gas phase distribution, the internal flow field and pressure field of the pump were obtained with inhomogeneous two-fluid model. The result showed that many gas accumulation zones accompanied vortices appears in the impeller as IGVF increases, and surge would occur as IGVF reaches a certain value. The change of IGVF would change the magnitude and direction of the impeller radial force.

当离心泵在小流量工况运行且传输介质为气液两相流时,含气率达到某一值时,会发生喘振现象,导致泵的扬程突降.本文采用计算流体动力学分析方法对一气液两相流离心泵进行了研究,通过对外特性曲线进行分析,发现了学者们所提到的喘振现象.为了提高离心泵在气液两相小流量工况下的水力特性,引入一种空腔结构,分析其对气液两相离心泵内部流场的影响及喘振的改善作用.结果 表明:在气液两相喘振工况下,空腔结构可以改善叶片正背面的压力分布,均匀气液两相在叶轮流道中的分布,有效减轻离心泵的气堵现象.因此,空腔结构不仅在结构上可以平衡叶轮、减轻泵的整体质量,还可以减轻流场中气液分离现象,避免喘振的发生,提高泵的水力性能.

为了研究进口含气率对气液两相流离心泵外特性以及内部流场特性的影响,该文采用计算流体动力学分析方法对某一气液两相流离心泵进行三维数值模拟研究.结果表明:扬程随着进口含气率的增加而降低,特别地,当进口含气率由3％增加到5％时,泵的扬程相对于纯水设计工况降低了37％;气液两相流工况叶轮流道会出现气体聚集区域,随着进口含气率的增加气体聚集区域面积也会增大;气体主要聚集在叶轮流道的上盖板附近,且随着进口含气率的增加气体聚集区向叶轮出口扩散.通过该研究得到以下结论:进口含气率的增加会导致泵的扬程降低;进口含气率会影响叶轮内部气体分布规律,进而影响内部流场,导致泵的性能发生改变.