【作者】 王准；

【导师】 施卫东；

【作者基本信息】 江苏大学 ， 流体机械及工程， 2008， 博士

【摘要】 本文主要研究了含柔性固体物料的两相流动,建立了其两相流动方程;研究了泵送两相流体时的性能变化的原因,并给出了预测性能变化的方法;从理论和试验两个方面研究了前伸式双叶片污水泵的设计和性能特点,并对该型泵叶轮内的固液两相流动进行了数值模拟。所做的创新性工作和得到的结论如下:(1)由于柔性物料与刚性固体不同,不但可以平动和转动,还会变形,因此分析其在液体中流动的难度增加。本文在简单介绍颗粒性固体物料两相流动方程后,采用拉格朗日法分析物体运动中的变形,给出了变形判别数G_t,得出了对于柔性固体物料,变形判别数G_t≠O;在此基础上,建立了其考虑时间和空间效应的一般性本构方程,并讨论了不同的本构方程的近似;给出了两流体模型的含柔性固体物料的两相流动瞬时局部方程。基于体积平均法,分析了应力张量和界面动量的传递,并对系数的选取进行了讨论,对稀相柔性固体物料的两相流动,忽略其碰撞项,建立了两相湍动方程,为稀相柔性固体物料的两相流动分析计算提供了理论基础和计算模型。(2)为了探讨泵在输送固液两相流体时的性能变化,从叶轮内部流动分析的角度,分析了固体在叶轮中的受力情况和流动速度等,并通过对不同密度下的叶轮内两相流动速度三角形分析,指出无论是ρ_s＞ρ_f,还是ρ_s＜ρ_f,时,固体相的圆周速度均小于液体相的圆周速度。因此,当泵输送两相流体时,相同流量下泵的扬程低于输送单相液体时的扬程。(3)收集了所能找到的相关文献中所有的泵在输送固液两相介质时的性能,根据这些数据,应用多元线性回归分析的方法得出了扬程降的公式。为了确定得到的公式精度,将根据得到的公式进行预测的预测值和各试验值、其他公式的预测值进行比较,结果表明本文计算公式的总体精度要高于其他计算公式的精度。且从公式的形式上来说,与以往的计算公式不同,在公式中考虑了叶轮的典型特征。(4)讨论了泵在输送两相流体时的功率、效率变化情况,推荐了计算功率、效率变化的公式。(5)基于一元理论,研究了前伸式双叶片污水泵的水力设计,指出在双叶片条件下,滑移系数大大增加,因而其出口直径和叶片宽度应在一般离心泵的基础上稍微加大。指出在叶片型线设计时,需要注意叶片前后盖板流线的包角差值和叶片前后盖板流线冲角的大小。对于蜗壳的水力设计,指出基圆直径应比一般离心泵的要大,喉部面积也宜相应加大。结合一个具体的实例,说明该型泵的设计方法和特点,并在同样的叶轮轴面图情况下,分别设计了叶片型线不同的两个叶轮。(6)结合CFD软件对所设计的两个叶轮进行了流动模拟。在流场求解的过程中,采用标准k—ε模型、SIMPLE算法、壁面函数等方法。分析了流场计算的结果,在流场计算的基础上进行了叶轮扬程和水力效率的预测。(7)对设计的两个不同叶轮进行了水力性能试验和通过性能试验,得到了两个叶轮及三次切割进口边后的扬程、效率、功率曲线和两个叶轮及第3次切割进口边后的固体颗粒、纤维的通过性能情况。水力性能试验结果表明:两种设计在规定点的性能参数均超过JB/T8857-1999《离心式污水潜水电泵型式与基本参数》标准的要求,其中一个叶轮对应的泵效率已经十分接近一般清水泵。但是两个不同的叶轮对应的泵相比,同样的轴面几何参数,不同的叶片型线,效率差别显著。叶片进口边切割的试验表明:叶片后盖板流线前伸,对叶轮的水力性能影响不大。通过性试验表明:前伸式双叶片结构可以提高叶轮的固体颗粒通过能力和抗缠绕能力。(8)CFD计算的结果和实际结果相比,CFD计算的结果要偏高,但是在同一叶轮的扬程和效率曲线的趋势上,在不同叶轮性能的对比上,CFD计算的结果是可信的,与试验结果基本一致,因此CFD技术可以作为叶轮优化水力设计的一个有力工具。(9)通过分析,得出前伸式双叶片污水泵具有好的通过性能的原因在于:①两叶片结构叶轮使得其固体颗粒通过能力优于一般污水泵。②叶片前伸,可以稍微提高叶轮进口处中心的压力,可以使叶轮进口处中心区域湍动也比周围区域要强烈,这两个原因使得叶片的抗缠绕能力提高。③叶轮叶片进口边与叶轮前后盖板的夹角发生变化,与一般叶轮有显著的区别,钝角不易形成流挂,因此前伸式双叶片表现出更好的抗缠绕能力。(10)选择混合模型对前伸式双叶片污水泵进行了两相流动计算。计算过程中为了更好地得出流动变化的情况,采用了网格白适应技术。计算时边界条件定义为:速度进口和自由出流出口;对于固体壁面边界,液体相壁面处默认为无滑移边界条件,固体相给出了速度变化的公式。计算得到了两相混合物的压力分布、液体和固体相流动速度分布、液体和固体相湍动能分布以及固体相的流动轨迹。与单相液体的流场计算结果比较表明,在输送两相流体时地扬程要低于输送单相流体时的扬程;在叶轮进口轮毂处,湍动最为激烈,纤维性物料在这里难于形成流挂,有利于纤维性物料的通过。更多还原

【Abstract】 The deformable solid two-phase flow, the performance changes of sewage pump delivering solid two-phase fluid, the design and performance characteristic of forward-extended double blade sewage pump were studied in this paper. By using of Lagrange method, it analyzed deformability of deformable solid and gave out the general constitutive equation of deformable solid. The turbulent equations for sparse deformable solid two-phase flow were developed. Analyzing experiment data from almost all related public literatures, it gave out the formulation to prediction the performance change of sewage pump delivering solid two-phase fluid. It also studied the performance characteristic of forward extended double blade sewage pump and its hydraulic design in the view of theory and experiment. Finally the two-phase flow within the impeller of forward-extended double blade sewage pump was stimulated. The main works are as following:(1) The main difference between deformable solid and other solid is that it not only moves, but also deforms while flowing. So it is difficult to describe its movement. After simply introducing the equations of particle solid two-phase flow, the paper focused on the deformable solid two-phase flow. By using of Lagrange method, the paper analyzeddeformability of deformable solid and gave out the differentiating number G_t.The general constitutive equation of deformable solid considering time effect and spatial effect was developed, then its approximate constitutive equation was discussed. Transient local equations for deformable solid two-phase flow based on two-fluid model were developed. Neglecting collision item, analyzing the stress and the momentum transfer of the interface, the volume averaging turbulent equations for sparse deformable solid two-phase flow was given out which can be applied to numerical stimulation of this type of two-phase flow.(2) For the purpose of studying the performance change of pump delivering solid two-phase flow, the velocity and stress of two-phase flow within impeller were analyzed. It concluded that whether the density of solid is larger than liquid or not, V_u of solidphase is smaller than that of liquid phase, and the total head of pump when delivering two-phase flow is smaller that when delivering single liquid phase at the same flow rate.(3) The data concerned with performance changes of pump delivering solid two-phase fluid from almost all the public literatures was concentrated. According to the data, the formulation on the head reduce of pump delivering solid two-phase was developed by using multiple variable linear regressive method. The difference between the formulation and others is that it considers the effect of pump typical configuration. The calculation results of the formulation and other formulations, the test results were compared. It illustrates that the formulation of this paper is more accurate than others.(4) The power and efficiency change of pump delivering solid two-phase fluid were discussed. Formulations for predicting the power and efficiency change were recommended.(5) Based on the one dimension theory, it studied the hydraulic design of forward-extended double blade sewage pump. In the case of double blades, the slipping coefficient of impeller is much larger than general centrifugal impeller. So the diameter and breadth of impeller should be augmented. Attention should be paid to the deference of wreathing angle and stagger angle between the two streamlines of back shroud and forward shroud. As for the hydraulic design of volute, its basic circle and tip area may be larger than others. As an example, two different hydraulic designs of this kind of impeller with the same axial section and different streamlines of blade for the same performance parameters were given out to show the specialty of its design.(6) The flow within the two designed impeller was stimulated with standard k-εmodel, SIMPLE arithmetic and standard well function. Analyzing the simulation result, the head and efficiency of impeller were predicted(7) By the test of hydraulic performance and the passage capacity, the performance curves (head, efficiency and power curve), the capacity of particle solid and fiber of the two different impeller and impeller of which the blade inlet even three times incised were gained. The hydraulic test shows that the performance of two different impellers meet the requirements of standard JB/T8857-1999《centrifugal sewage submersible pump model and performance parameters》, the efficiency of one of them is very close to general water pump. But the efficiency of two impelles is obviously different, forward extending inlet of blade has little influence on the hydraulic performance. The passage capacity test shows that impeller with double forward-extended blades features better capability for particle solid to pass and better anti-winding ability.(8) Compared the result of numerical simulation of the flow within impeller with the test result, it concluded that the result of numerical simulation is some higher, but the both are consistent in the view of changing trend of performance curve for the same impeller and the compare of the performance of different impeller. So numerical simulation is reliable to some extent, and is helpful for optimizing hydraulic design of pump.(9) The reasons for better passage capability of forward-extended double blade sewage pump are that: (a) with double blades, the larger tunnel of impeller avail for particle solid to pass through. (b) Forward extending blade can slightly enhance the center pressure and turbulence of impeller inlet. Then the anti-winding ability is improved. (c) The angle between the inlet of blade and shroud is obviously different from other centrifugal impeller, which enhance its anti-winding ability.(10) Simulating the solid-liquid two-phase flow within the double forward-extended double blade impellerwith mixture model. For bettering calculation, self-adapting technology was used. The boundary condtion defined as following: Velocity inlet and outflow, non-slip well boundary for liquid phase but velocity formulation coming from literatures concerned well boundary for solid phase. The pressure distribution of the mixture, the velocity distribution and the turbulent kinetic energy distribution of liquid phase and solid phase, the track of solid phase flow were given out. The calculating result shows that the total head of forward-extended double blade sewage pump delivering the mixture of solid-liquid two phase is lower than delivering liquid single phase, the turbulent kinetic energy in the vicinity of inlet hub of impeller is large which is helpful for fiber to pass the impeller.更多还原