Some features of molecular flow in a rotor-stator row with real topology

Free molecular flow within rotor and stator rows of a turbomolecular pump is simulated using test-particle Monte Carlo method. The solution is performed in an inertial reference frame where molecular paths are straight lines. The molecules are followed both in rotor and stator in a similar system of coordinates. The real three-dimensional topology of the blade rows including blade thickness, clearance between blade tip wall and casing, and the gap between rotor and stator are considered. Good agreement between numerical results of several rotor-stator combinations and known experimental data confirms the validity of the presented algorithm. The flow analysis shows that although the molecules tend to collect in high radius region, however the concentration of molecules attenuates in the clearance region of rotor, and accentuates in the clearance region of stator. Parametric study of a rotor-stator row shows that the effect of the gap between rotor and stator is significant for the first stages of TMPs with large blade angles and wide spacings, while it is negligible for the last blade rows with small angles and small spacings.     

泵内压降和水力损失耦合诱导泵内液氮空化研究

为了研究泵内压降和水力损失耦合诱导泵内液氮空化,采用Zwart空化模型和RNG k-ε湍流模型,并使用CEL语言将饱和蒸气压随温度变化函数关系式导入CFX软件中进行求解,对不同流量下低温泵的空化特性曲线进行分析。研究结果表明,低温泵内压力、温度和空泡体积分数分布与空化的发展程度有关,由于水力损失的作用,小流量工况下,泵内会出现涡状流,从而对叶轮内空化产生影响。     

The influence of cavitation on the flow characteristics of liquid nitrogen through spray nozzles: A CFD study

Spray cooling with cryogen could achieve lower temperature level than refrigerant spray. The internal flow conditions within spray nozzles have crucial impacts on the mass flow rate, particle size, spray angle and spray penetration, thereby influencing the cooling performance. In this paper, CFD simulations based on mixture model are performed to study the cavitating flow of liquid nitrogen in spray nozzles. The cavitation model is verified using the experimental results of liquid nitrogen flow over hydrofoil. The numerical models of spray nozzle are validated against the experimental data of the mass flow rate of liquid nitrogen flow through different types of nozzles including the pressure swirl nozzle and the simple convergent nozzle. The numerical studies are performed under a wide range of pressure difference and inflow temperature, and the vapor volume fraction distribution, outlet vapor quality, mass flow rate and discharge coefficient are obtained. The results show that the outlet diameter, the pressure difference, and the inflow temperature significantly influence the mass flow rate of spray nozzles. The increase of the inflow temperature leads to higher saturation pressure, higher cavitation intensity, and more vapor at nozzle outlet, which can significantly reduce mass flow rate. While the discharge coefficient is mainly determined by the inflow temperature and has little dependence on the pressure difference and outlet diameter. Based on the numerical results, correlations of discharge coefficient are proposed for pressure swirl nozzle and simple convergent nozzles, respectively, and the deviation is less than 20% for 93% of data.     

Increasing flow efficiency of high-pressure and low-pressure steam turbine stages from numerical optimization of 3D blading

3D blading of a high-pressure and low-pressure steam turbine stage is optimized using Nelder–Mead method of deformed polyhedron. Values of the minimized objective function, i.e. stage losses with the exit energy are found from 3D viscous compressible flow computations, including turbulence effects. Among the optimized parameters are stator and rotor blade numbers and stagger angles, rotor blade twist angle, stator blade sweep and lean, both straight and compound. The blade sections (profiles) are assumed not to change during the optimization. There are constraints imposed on the design parameters, including the mass flow rate and stage reaction. Optimization gives designs with new 3D blade stacking lines, and with increased efficiencies, compared with the original design.     

CFX-BladeGen在涡轮叶片造型中的应用

涡轮钻具中的主要元件是由定子和转子组成的涡轮,它的作用是把液体能变为主轴上的机械能。将CFX-BladeGen应用于涡轮钻具叶片的造型,并对生成的模型进行数值模拟计算。计算结果与同类型涡轮钻具台架实验的数据比较表明,CFX-BladeGen可以比较方便、快捷地满足涡轮叶片造型要求。     

动静圆柱坐标系下Navier-Stokes方程的分区算法

通过耦合相对和绝对圆柱坐标系下的三维Navier-Stokes方程,本文采用高精度高分辨率的三阶ENN格式及LU-SGS隐式解法进行子域求解;提出了动静子域干涉面的重合处理与重叠处理,并最终发展了一种新的分区算法。通过对某带进口导叶的三级轴流压气机的数值实验,验证了该分区算法的有效性,计算结果与实验数据吻合较好。     

Vessel diameter and liquid height dependent sonication-assisted production of few-layer graphene

Sonication-assisted liquid-phase exfoliation of graphite makes facile, scalable, and low-cost graphene production possible, but there is little information about how sonication-related factors such as vessel diameter (D) and liquid height (H) affect this process and how to scale-up this technique. In this article, the dependence of the sonication-assisted few-layer graphene (FLG) production on D and H was investigated based on experiments and numerical simulation which was performed by finite element method to determine cavitation-related parameters. It was found that by essentially changing the cavitation phenomenon, D and H could critically affect the FLG concentration, FLG yield, injected power, and production efficiency. Combined experimental and simulational analyses reveal that though D and H can change both cavitation volume and cavitation volume fraction, it is the cavitation volume fraction that directly relates to the FLG concentration and production efficiency with a monotonically increasing trend, while the FLG yield and injected power are almost proportional to the cavitation volume, which in turn follows a linear increasing trend with the sample volume. The practical importance for industrial FLG production may lie in the following: (1) D and H should be carefully designed to obtain high cavitation volume fraction to gain high production efficiency and FLG concentration or output-input ratio and (2) large D, H, or sample volume is necessary for achieving large cavitation volume to enhance the FLG yield. Moreover, enhancement in pressure amplitude or cavitation intensity could also favor FLG production. These results have verified the importance of D and H which are often ignored when studying graphene production, and will provide important information on designing large-sized vessels for mass-producing graphene by sonication.     

绕三维水翼非定常空化流动结构的数值与实验研究

为了说明非定常空化的流动机理,该文采用数值与实验相结合的方法对绕三维水翼片状和云状空化流动结构进行了研究.实验在高速水洞中进行,采用高速录像技术观测了片状和云状空化阶段的空穴形态.数值计算基于均相流模型,汽液混合区域密度由质量传输方程调节.利用商业软件二次开发技术引入准确描述空化流场非定常特性的FBM 湍流模型,进行绕三维水翼的数值模拟,获得了随时间变化的空穴形态、压力和速度分布等流场结构.与实验结果对比发现,数值计算结果与实验基本一致.在片状空化阶段,空穴稳定地附着在水翼表面,只有空穴尾部不断的有小空泡团沿着翼弦方向脱落.在云状空化阶段,清楚得描述了空穴的产生-发展-脱落-溃灭的准周期性变化,并准确地捕捉到空泡脱落时,附着在翼型前端的U 型空穴和翼展方向不同强度的反向射流,脱落的空泡由翼型中前部旋涡状脱落.     

高速定转子均质机转子叶片振动模态分析

采用对接加载模态综合分析法,将定转子均质机关键元件转子系统结构简化为叶-盘系统,对单个转子叶片进行有限单元划分,分析得出了转子转速为4 500 R／MIN时振动频率响应分布趋势;前10阶扩展模态分布具有一定的规律性,在初始4阶模态状态时频率波动小,且与系统固有频率近似;从第5阶模态以后分布波动较大, 且波动幅度很接近,约为20HZ。分析结果有利于定转子均质机关键元件转子系统结构的优化设计。     

附着型空穴断裂及脱落机制的实验研究

为深入研究附着型空穴断裂及空泡脱落机理,该文采用实验方法对收缩-扩张流道内的云状空化流动现象进行了研究。实验在空化水洞中进行,采用同步测量技术,通过高速摄像机和压力传感器同步获取了云状空化阶段的附着型空穴形态和壁面压力。研究结果表明,附着型空穴断裂及空泡脱落存在两种不同的机制:回射流机制和间断面推进机制。其中,回射流于附着型空穴尾部形成,紧贴壁面并持续向前推进,其厚度远小于附着型空穴厚度,在回射流向上游推进过程中,其覆盖区域壁面压力波动较小,当回射流运动到附着型空穴前缘,"剪断"附着型空穴,造成空穴断裂及脱落;附着型空穴内部形成的向上游推进的间断面是造成空穴断裂及脱落的另一种机制,间断面厚度为当地空穴厚度,间断面前后含气率差异较大,间断面前为高含气率的纯汽相区,间断面后为低含气率的水汽混合区。间断面向上游推进过程中,间断面位置处会出现压力尖峰,当间断面推进到喉口位置,带来喉口部位压力升高,降低了喉口位置空泡生成率,使得新生成的空泡与向下游运动的脱落型空泡分开,导致空穴断裂及脱落。     

Effects of casing treatment on behavior of tip leakage flow in an isolated axial compressor rotor blade row

This article deals with enhancement in aerodynamic performance of an isolated axial compressor rotor blade row while applying treated casing. Three dimensional unsteady flow is assumed and a flow solver, utilizing Large Eddy Simulation (LES), is undertaken for the numerical calculations. Unsteady tip leakage flow and its propagation trajectory are simulated in detail for both smooth and treated casings. Oscillatory nature of tip leakage flow is depicted and its frequency is calculated by the calculation of pressure distribution along the rotor blade tip, for smooth and treated casings. For the smooth casing and in comparison with experimental data, results showed that in contrast with the Reynolds Averaged Navier–Stokes method, the LES realizes dependency of frequency characteristics of the tip leakage flow on the blade tip clearance size, and also can recognize different frequency characteristics of the tip leakage flow along the blade chord. Results also demonstrated that performing casing treatment causes the amplitude of unsteadiness of tip leakage flow to reduce and its frequency to get closer to the blade passing frequency. This in turn, causes flow blockages and losses in total pressure to reduce.     

Bezier函数型径向弯叶片对电站锅炉给水泵空化性能影响研究

为满足1000 MW超超临界电站锅炉给水泵大容量高参数的设计要求,通过CFD技术对锅炉给水泵叶轮的空化性能进行数值研究．提出一种基于Bezier 函数思想的径向弯叶片几何参数设计方法,并引入正弯叶片和反弯叶片两种叶片径向弯曲结构．结果表明：直叶片必需空化余量为22.8 m,与试验值的绝对误差仅为0.2 m,预测结果具有一定的精度;反弯叶片必需空化余量为22.3 m,空化性能最好;正弯叶片在叶片进口处压力面最先出现空泡,吸力面空化面积最大,而反弯叶片吸力面空化面积最小;3种径向弯叶片空化后在沿叶高中间流线相对位置0.2处叶片表面存在最大压差,可能导致叶片局部发生断裂．     

Experimental investigation of losses and secondary flow in an axial compressor stage

A detailed investigation of a three-dimensional flow using both stationary and rotating pressure probes has been carried out in a low speed axial compressor stage. At the casing of a rotor row there is secondary flow produced by the relative motion of the annular wall to rotor blade tip and the tip clearance flow. At the hub a channel vortex can be observed. The value of the loss coefficient of both rotor and stator rows determined from conventional pressure probe data is affected by flow unsteadiness. This effect has been considered in detail. As a result, the probes should be dynamically calibrated. The rotor and stator blade elements loss at mid-span approximately equals two-dimensional cascade loss, when the data of probes exposed to strong flow unsteadiness have been corrected. This work was done for CKD-Works in Prague. The author is grateful to Dr.Svoboda of CKD for the permission to publish the results. Thanks are also due to Dr.Z. Moravec and Dr.J. Citavy for useful discussions.     

液力透平蜗壳内非定常压力脉动的研究

液力透平内部流场的非定常压力脉动是影响机组运行稳定性的关键因素之一,为了研究液力透平蜗壳内部的压力脉动,采用流场分析软件对一单级液力透平内部流场进行了三维定常和非定常数值模拟,对蜗壳流道内不同周向位置、径向位置和不同流量时的压力脉动进行了时域和频域分析。结果表明:在一个叶轮旋转周期内蜗壳内压力的脉动数量等于叶片数;蜗壳入口位置和割舍位置处压力脉动较小,蜗壳环形部分中部和割舍前端位置处压力脉动较大;蜗壳内压力脉动的主频和次主频分别为叶频和2倍叶频;液力透平蜗壳内部的压力脉动程度在小流量下较小,随着流量的增加,压力脉动程度逐渐增加,大流量时最为剧烈。为了验证数值计算的准确性,建设了开式液力透平试验台,制造了模型样机对液力透平进行了外特性试验和非定常压力脉动测量,验证了数值计算的准确性。     

亚声速轴流风扇静子宽频辐射噪声预报与参数影响研究

为预报亚声速轴流风扇静子的宽频辐射噪声,介绍并推导了叶栅宽频辐射声功率计算表达式,考虑到工作在转子尾流中静子的情况,采用Park-Gauss尾流模型模拟转子尾流,建立转子尾流三维湍流波数频率谱模型,推导得到考虑转子尾流作用的静子宽频辐射声功率级计算公式。通过与Boeing和NASA风扇模型试验结果对比,结果显示上述公式较Hanson计算公式能够更准确的预报静子的宽频辐射声功率级,其预报结果与试验结果相差在5 dB以内。在NASA风扇模型的基础上改变静子叶片设计参数,显示减少静子叶片数可在高频段降低风扇的宽带噪声。     

多排环境下转子叶片气动弹性稳定性机理分析

传统叶片颤振分析多是基于单转子研究模型,发动机的紧凑性要求导致级间距减小,多排耦合作用对颤振的影响将不容忽视。采用自行开发的程序对某型1.5级高压压气机进行了流固耦合数值模拟,分析上、下游叶排对转子叶片颤振特性的影响。针对典型工况,分别进行了单转子模型,导叶转子模型,转子静子模型,导叶转子静子模型的叶片气动弹性稳定性分析。研究表明,激波振荡对颤振特性影响显著;多排环境下存在非定常压力波的反射和叠加,明显改变转子叶片表面的非定常压力幅值和相位,进而改变转子叶片气动弹性稳定性。多排干涉作用提高了转子叶片的气动阻尼,尤其是上、下游叶排同时作用时阻尼提高了近732.7%。     

混流泵启动过程非稳态空化的试验研究

为了分析混流泵启动过程瞬态扬程理论模型的适用性及非稳态空化过程,通过高速摄影和压力测量试验,探讨不同空化数、不同流量工况下启动过程中叶顶区空化状态特性。试验研究结果表明,已有理论模型可应用于混流泵启动过程,同时验证试验结果准确性。在启动过程中,空化最先发生在叶顶区域头部。当启动完成时,叶顶空化区域可分为两部分,一部分为出现在叶顶区的三角形的空化云团;另一部分为刮起涡空化。在同一流量工况下,随着空化数降低,垂直空化涡会在启动过程中出现并且发展。在同一空化数下,随着流量减小,垂直空化涡延迟出现,并且空化区域减小。     

前飞状态下直升机旋翼旋转噪声预测

基于Farassat声学时域公式1A,建立了一个亚音速前飞状态下直升机旋翼旋转噪声的预测方法。该方法将厚度噪声与载荷噪声之和作为总噪声,将桨叶表面沿展向和弦向进行数值离散,延迟时间采用牛顿法求解,通过坐标转换,可针对不同位置观察点计算出声压的时间历程。并进一步利用傅立叶分解,进行噪声的频谱分析。应用该方法,分别进行声压与频谱的算例计算,并与可得到的试验数据进行了对比,验证了方法的有效性。在此基础上,着重分析了桨叶片数、旋翼转速、前飞速度等参数对旋翼气动噪声的影响,得出了一些有意义的结论。     

汽轮机叶顶汽封泄漏涡诱导下的压力脉动研究

以某汽轮机级为研究对象,采用三维非定常数值模拟的方法,研究了动叶顶部汽封泄漏涡的涡动特性和泄漏涡影响下汽封腔室内的压力脉动规律。结果表明:叶顶汽封腔室内存在周向螺旋状涡与壁角涡组成的多尺度涡系,涡系的位置和影响范围会随时间经历复杂的变化。叶顶汽封腔室内的压力脉动频率中兼具叶轮旋转的周期性频率和溃散为小尺度涡结构后的高频率。间隙内的多尺度涡结构和动静叶间交替变化的压力场在汽封间隙内的传播是引起汽封腔室内周向压力不均的主要原因。     

A study on the pumping performance of the disk-type drag pumps for spiral channel in rarefied gas flow

The pumping characteristics of a single-stage disk-type drag pump (DTDP) are calculated for the variation of the vertical clearance between a rotor and stator by the three-dimensional direct simulation Monte Carlo method. The gas flow mainly belongs to the molecular transition flow region. Spiral channels of a DTDP are cut on both the upper and lower sides of rotating disks, but the stationary disks are planar. The interaction between molecules is described by the variable hard-sphere model. The no-time counter method is used as a collision sampling technique. As a consequence of results, the vertical clearance between a rotor and stator has a significant effect on the pumping performance. Experiments are performed under the outlet pressure range of 0.4-533 Pa. When the numerical results are compared to the experimental data, the numerical results agree well qualitatively.