Study of aircore phenomenon and influence of water height during liquid draining

Draining of liquids through cylindrical tanks is a very common phenomenon and has many applications. Understanding the aircore formation and its growth during draining has attracted appreciable interest in the literature. In this study, water draining through cylindrical tanks was studied using experimental and numerical techniques. Eight different initial heights of water in the tank between 310 and 450 mm with a 20-mm increment were tested in each experiment. The numerical study shows good agreement with the experimental data and promotes understanding of the generation and disappearance of an aircore during draining. For the different initial water heights, the experiments were performed with and without initial rotation of the tank. It is found that in the experiments without initial tank rotation, the drain time of water increases with increasing initial height. On the other hand, the drain time remains almost the same for all initial heights tested with initial tank rotation. The small variation in the drain time even when the initial water level is reduced is explained by the aircore duration during draining. Also, the mechanism of generation and disappearance of aircore is proposed with the help of numerical results.

     

Electromagnetic vortex suppression to prevent air core phenomenon for draining of electrically conducting liquids

Journal of Mechanical Science and Technology - The air core phenomenon observed during liquid suction or drainage through a narrow drain port can be reproduced artificially by starting the draining...     

吸入室直径对液气射流泵流场特性影响的数值模拟

为了全面分析液气射流泵内部结构对液气射流泵吸气性能的影响,以提高液气射流泵整体吸气性能。利用Fluent软件对不同吸入室直径下液气射流泵内部流场进行了三维数值模拟,获得了液气射流泵内部压力场和速度场分布以及轴心静压曲线,并拟合出压力比、流量比、效率与不同吸入室直径的关系曲线。对比分析表明,吸入室直径的大小会对液气射流泵内部压力、速度及吸气效率产生很大影响。射流泵其他结构一定时,吸入室直径大小存在最优值或者最优范围,使得液气射流泵的吸气性能最佳。     

Prevention of air entrainment during liquid draining using disc-type vortex suppressor

After rotating a cylindrical tank containing a liquid at a constant rotation speed, by draining the liquid freely, an air-core phenomenon (that is, air is entrained into the drain port along a vortex flow) can be forcibly reproduced. This vortex phenomenon occurs very frequently in a variety of actual drainage situations and generally has a negative impact on many industrial devices, including reductions in drain speed, a noise and vibration, and structural damage of turbo machineries. The present study suggests a simple and very effective vortex-suppression device through physically analyzing the causes of the air-core phenomenon. In this study, liquid drainage processes with and without the suggested disc-type vortex suppressor were investigated numerically and experimentally. Through the numerical simulation, the internal flow characteristics have been investigated and the mechanism of the air-core formation has been revealed. As well, the experiments of varying the dimensions of the suggested disc-type vortex suppressor have been carried out. The velocity vector, drain water level, and vorticity distribution were compared for cases with and without the suggested vortex suppressor.     

Design of port plate in gerotor pump for reduction of pressure pulsation

The pressure pulsation due to the gear geometry of the gerotor (generalized rotor) pump mainly occurs in an instant that the chamber of the gerotor enters the delivery port and leaves the suction one. Such a pressure pulsation may result in undesirable vibration and noise of pump components as well as cavitation in hydraulic system. Therefore, it is very important to examine the pressure characteristic of the gerotor pump at its design and analysis stages. In this paper, in order to reduce the pressure pulsation in the gerotor pump, the port plate with the relief grooves is designed by referring to as notch of vane pump and relief groove of piston pump. A series of the theoretical analyses on the pressure pulsation is performed in consideration of various design parameters of the port plate, including the installation positions of the port inlet/ outlet and the groove width, and the operating conditions such as rotational velocity and delivery pressure.     

Maximum suction lift of water jet pumps

This paper describes an experimental study on water jet pumps with different diameters and nozzle-to-throat area ratios. The results revealed that the area ratio was an important parameter to characterize the maximum suction lift of the jet pumps, while their diameters had a negligible effect. All jet pumps reached the cavitation regime at a suction lift of about 8 mH₂O. In the non-cavitating region, it was found that the higher the area ratio, the higher the maximum suction lift for the same motive pressure head. However, the lower the area ratio, the higher the resistance to enter the cavitation regime. A dimensionless correlation was obtained for the non-cavitating region to describe the maximum suction lift as a function of a modified Thoma number and the area ratio. Curve fitting of experimental data also provided a dimensionless correlation to predict the onset of cavitation. Finally, applications of the results are presented.     

单螺杆膨胀机泄漏通道长度变化规律的理论分析

对于回转式的容积型膨胀机,内部泄漏是影响其性能的重要因素。单螺杆膨胀机具有复杂的三维空间结构,使得其内部泄漏规律变得很复杂。为了研究单螺杆膨胀机内泄漏规律,从单螺杆膨胀机的几何结构出发,建立泄漏通道长度的数学模型,并分析进气孔口,螺杆直径和星轮直径等因素对泄漏通道长度的影响规律。结果表明,在进气过程中,当进气孔口完全加入时,泄漏通道L9达到最大值,在膨胀过程中,泄漏通道的长度大小关系依次为L8>L7>L1+L2+L4>L9>L6>L3+L5;单螺杆膨胀机螺头处泄漏通道的长度与内容积比有关,进气过程螺头处泄漏通道的长度随着内容积比的增大而减小;在内容积比不变的情况下,螺杆直径和星轮直径相等(等径)时,直径越大,泄漏线越长,且螺杆直径和星轮直径不相等(不等径)的泄漏线比等径时的更长,受进气孔口的影响更大。通过上述工作,为单螺杆膨胀机内泄漏量的分析计算提供基础数据,并为单螺杆膨胀机的结构优化提供理论指导。     

涡旋液泵内部非稳态流场的数值模拟

采用动网格技术对涡旋液泵内的非稳态流动进行了数值模拟,得到了泵在各个转角下的压力、速度、空泡体积分数,以及进出口流量和监控点的压力参数。结果表明,涡旋液泵内的流动是一种非稳态、非均匀,非对称的流动。动静圈的啮合间隙处因大压差和小流通面积而存在高速射流现象,并在啮合间隙下游出现负压区和空化。泵进口位置的偏移和动盘对腔外流体的推动使左右两个吸液腔的流动不对称,将造成涡盘受力的不平衡。在吸液即将结束时,因涡旋液泵对液体的挤压作用,在大约20°的转角范围内,泵的工作腔内出现极大幅值的压力脉动,严重危害泵的安全可靠运行。     

PIV study of vortexing during draining from square tanks

The flow field in square tanks with various corner roundings is studied to investigate drain flow characteristics. An attempt is made to understand the mechanism of flow field responsible for vortex suppression by the different radius of rounding at the corner. For this purpose, flow visualization studies using particle image velocimetry are employed to determine the flow patterns in a square tank. Results are obtained for no draining and with draining experiments. The flow field is visualized both in horizontal and vertical planes. The results reveal that the secondary vortices formed at the corners are responsible for vortex suppression.     

某型号液压打桩机环形阀组回油流场理论计算与仿真分析

液压打桩机是利用液压油压力来传递动力,驱动打桩锤进行打桩作业的装置,在海洋工程领域有着广泛应用,为获得某型号液压打桩机环形阀组回油流场特性,对其进行了理论计算与仿真分析。首先通过数学模型从理论上计算出回油流道的压力损失;然后利用Fluent仿真软件得到了回油流道在不同阀口开度下的压力云图以及速度云图;最后在不同阀口开度下将理论计算与仿真模拟结果进行了对比。结果表明:理论计算结果与仿真模拟结果趋势相同,并且流体在阀芯表面会形成局部高压,在阀口周围以及阀芯中部的局部表面会产生旋涡。研究成果为液压打桩机中环形阀组的设计提供了一定参考和借鉴。     

Analysis and design of an axial piston water-pump with piston valve

In this paper, we present a novel axial piston water-pump with piston valve, which carries out the flow distribution to drain and sucks water by the interaction of each piston. This novel water-pump could achieve change in-phase between flow rate and the passage areas of the intake and outlet ports. In order to completely achieve the in-phase change, the pressure that is assigned a fixed value in the piston chamber is optimized. On these grounds, the optimum shapes of the intake and outlet ports have been found to be rectangular according to theoretical analysis. The simulation results indicated that the optimum intake and outlet port shapes keeps the pressure in the piston chamber constant, and there is almost no pressure surge except for a very small pressure wave in the piston chamber. Finally, the test of model machine showed that the pressures of the intake and outlet port are very steady, but the leakage is large and the volumetric efficiency is 74.7%.     

承压设备的带压引流焊接密封

介绍了承压设备在泄漏状态下进行带压密封的一种新方法——引流焊接法。论述了引流焊接法的基本原理，承压设备带压焊接的法律依据，允许带压焊接最小壁厚的计算方法，引流器的强度计算公式。给出了管式、板式和盒式三种引流器的结构形式，12条带压引流焊接操作注意事项。并给出3个典型的成功实例论证了带压引流焊接密封技术在承压设备泄漏事故中的应用效果。     

系列颗粒浆液泵吸排浆球阀的设计

通过合理的结构和参数设计，研制了一种新颖独特的吸排浆球阀。该球阀可用于液压柱塞泵和气压活塞泵等系列泵，以满足其不同流量和压力并能输送颗粒浆液的要求。     

Influence of swirl on the discharge coefficients of sonic nozzles

Flow characteristics of a swirl generator are studied using an open circuit flow loop, and influence of upstream swirl on the discharge coefficients of sonic nozzles is investigated using a high pressure gas flow standard measurement system. The open circuit flow loop consists of swirl generator, testsection, sonic nozzle, suction fan and LDV system. The gas flow measurement system comprises two compressors, storage tank, temperature control loop, sonic nozzle testsection, weighing tank, gyroscopic scale and data acquisition system. Experiments are performed at various nozzle throat diameters, inlet pressures and angles of swirl generator. As the angle of swirl generator becomes larger, axial velocities decrease near the wall and rapidly increase in the pipe core, and swirl velocities increase to form swirl flow. Influence of upstream swirl on discharge coefficients becomes greater as the intensity of swirl increases and as the nozzle throat diameter is enlarged. Variation trend with Reynolds number, however, is very similar each other regardless of swirl intensity.     

空心线圈式电流互感器的干扰磁场研究

电子式线圈电流互感器的原理、结构及输出信号等与传统的电磁式电流互感器有很大不同,其性能会受外界磁场等因素的影响。本文对影响空心线圈电流互感器性能的电磁干扰因素进行详细分析,在理论分析的基础上给出相应的改进措施。实验表明,改进后的空心线圈电流互感器受外界磁场的影响很小,互感器的稳定性满足实用化要求。     

Gasoline spray characteristics impinging onto the wall surface in suction air flow

This study investigates the spray characteristics before and after wall impingingment of gasoline spray in suction air flow. For this study, a rectangular model intake port was made of acrylic glass, and suction air was generated by using the forced air blower contrariwise. The injector for this study was a pintle-type port gasoline injector in which an air-assist adaptor is installed to supply assisted air. A PDPA system was employed to simultaneously measure the size and velocity of droplets near the wall. Measured droplets are divided into “pre-impinging droplets” with positive normal velocity and “post-impinging droplets” were negative normal velocity for the suction flow. The velocities, size distributions and Sauter mean diameter (SMD) of pre- and post-impinging droplets for varions injection angles and air-assists are comparatively analyzed.     

Relation between pressure variations and noise in axial type oil piston pumps

Pressure variation is one of the major sources on noise emission in the axial type oil piston pumps. Therefore, it is necessary that the pressure variation characteristics of the oil hydraulic piston pumps be clarified to reduce the pump noise. Pressure variations in a cylinder at the discharge region and the pump noise were simultaneously measured with discharge pressures and rotational speeds during the pump working. To investigate the effects of the pre-compres-sion and the V-notch in the valve plate, we used the three types of valve plates. In this research, it is clear that the pressure variation characteristics of axial type oil piston pumps is deeply related to the pre-compression and to the V-notch design in valve plate. Therefore, we could reduce the pump noise by using the appropriate pre-compression angle and the notch design that are between the suction port and the discharge port in valve plate.     

液压轴向柱塞泵配流盘气蚀机理

对轴向柱塞泵配流盘进行气蚀试验。在试验条件相同的情况下,根据减压槽处结构不同的配流盘,得到两种截然不同的气蚀破坏结果。针对试验中两种配流盘的配流过程进行计算流体动力学(Computational fluid dynamics,CFD)解析,得到了配流盘不同位置的速度分布,以及压力、速度随缸体转角的变化曲线;得出配流盘发生气蚀的机理,即气蚀不仅取决于配流盘附近的速度和压力大小,还取决于速度的方向——射流角;提出通过改变配流盘结构,将油液回冲阶段初期的射流角控制在30°～60°内来减少配流盘上气蚀的方法。根据配流盘气蚀产生的机理将油液回冲阶段初期的射流角控制在30°～48°,经过试验,就气蚀破坏来讲配流盘的寿命延长到了原来的4倍多。     

渣浆泵叶轮湍流场模拟及颗粒轨迹分析

为提高渣浆泵的抗磨性能并优化泵的设计,采用RNG κ-ε湍流模型和SIMPLEC算法对多工况下渣浆泵叶轮内部清水流场进行了数值计算,得到叶片表面相对速度矢量分布,分析了叶片表面回流、旋涡现象;基于单颗粒动力学模型,采用拉格朗日法计算了多工况下固相颗粒的运动轨迹,分析不同粒径颗粒对叶片表面磨损的影响。结果表明：叶片压力面进口在大流量工况下开始出现回流,而叶片吸力面进口则在小流量工况下回流、旋涡严重,叶片进口的回流、旋涡不仅容易引起NPSHr增高,诱发空化现象,还会导致颗粒聚集、反复冲击该区域;在小流量工况下,叶片压力面出口和吸力面出口均出现大区域的回流,甚至延伸至叶片中段,随着流量增大,回流和旋涡区域逐渐缩小,由此可见叶片出口在小流量工况下的磨损比较严重;其他因素一定时,固液混合物的流量越小,颗粒在进入叶片流道前停留的时间越长,导致颗粒与叶片头部的碰撞概率增大;随着颗粒直径增大,颗粒向叶片压力面靠近的趋势越明显,与压力面的碰撞机会也增多,从模拟结果可以看到,该叶轮对1mm以上的大颗粒适应性不好,在设计流量工况下,0.5~1mm粒径范围内颗粒适应性最好。     

民机发动机驱动泵的长寿命设计技术

针对民用飞机特点,提出了民机发动机驱动泵长寿命设计技术。分析了入口内置涡轮增压泵、出口集成压力脉动衰减缓冲瓶、壳体回油腔设置主动抽油泵对发动机驱动泵寿命的影响,并进行了仿真分析和试验验证。结果表明:入口腔内置涡轮增压泵可将入口压力增加0.15 MPa,出口集成缓冲瓶可将液压泵压力脉动控制在额定输出压力±3%以内,且缓冲瓶容积越大,对压力脉动衰减越明显,壳体回油腔设置主动抽油的摆线齿轮泵可将液压泵壳体回油相对入口的温升控制到小于6 ℃,壳体回油温度甚至低于泵出口温度。