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Effect of Compressibility on Velocity Profile and Friction Factor of Gaseous Laminar Flows in a Microtube 可压缩性对微管内气体层流速度分布和摩擦系数的影响
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-11-01 DOI: 10.1115/1.4051422
S. Murakami, Kaoru Toyoda, Y. Asako
Laminar flow of nitrogen gas in a microtube was simulated numerically to obtain velocity profile and Fanning friction factor in a quasi-fully developed region. The numerical procedure based on Arbitrary-Lagrangian-Eulerian method solved two-dimensional compressible momentum and energy equations. The computations were performed for a wide range of Reynolds number in laminar flow regime with adiabatic wall condition. It was found that the velocity profile deviates from the parabola as Mach number increases, and the product of Fanning friction factor and Reynolds number is not a constant but a function of only Mach number. To explain the compressibility effect, a new theoretical flow model which gives the velocity profile of gaseous laminar flows in a microtube was proposed under the assumption of purely axial flow. The theoretical velocity profile is taking radial-direction density change into account, and coincides with the numerically obtained velocity profile. The proposed flow model also shows that the Fanning friction factor of a compressible flow in a microtube is expressed by a quadratic function of Mach number. The coefficient of the Mach squared term is 40% of the numerically obtained correlation. The compressibility effect on friction factor of gaseous laminar flows in a microtube partly results from velocity profile change which must occur to keep the mass velocity profile when density changes in radial direction. The remainder of the compressibility effect can be considered to result from actual mass transfer in the radial direction whose existence was demonstrated by the numerical results.
对氮气在微管中的层流进行了数值模拟,得到了准完全发育区域的速度分布和范宁摩擦系数。基于任意拉格朗日-欧拉方法的数值计算程序求解了二维可压缩动量和能量方程。在具有绝热壁条件的层流流态下,对大范围的雷诺数进行了计算。随着马赫数的增加,速度分布偏离抛物线,范宁摩擦系数与雷诺数的乘积不是一个常数,而只是马赫数的函数。为了解释可压缩性效应,在纯轴向流动假设下,提出了一种新的理论流动模型,给出了微管内气体层流的速度分布。理论速度剖面考虑了径向密度变化,与数值计算速度剖面吻合。该流动模型还表明,微管内可压缩流动的范宁摩擦系数可以用马赫数的二次函数表示。马赫平方项的系数是数值计算得到的相关系数的40%。微管内气体层流的可压缩性对摩擦因数的影响部分是由于当密度在径向方向发生变化时,为了保持质量速度分布,必须发生速度分布的变化。剩余的可压缩性效应可以认为是由径向的实际传质引起的,其存在已被数值结果所证实。
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引用次数: 2
Thermodynamic Effects on Pressure Fluctuations of a Liquid Oxygen Turbopump 液氧涡轮泵压力波动的热力学影响
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-11-01 DOI: 10.1115/1.4051218
Deyou Li, Zhipeng Ren, Yu Li, Boxuan Miao, R. Gong, Hongjie Wang
Liquid oxygen turbopumps are an important component of rocket engines. The instability induced by cavitation flow in turbopumps has received considerable attention because of thermodynamic effects. In this study, unsteady numerical simulations of a turbopump with thermodynamic effects were performed. The frequency composition and source of pressure fluctuations in a turbopump were analyzed, and the difference in pressure fluctuations with/without thermodynamic effects was revealed. The results showed that the pressure fluctuations were mainly caused by the interaction between the impeller and diffuser, and the thermodynamic effects slightly increased the amplitudes of the characteristic frequencies. In addition, in the inducer and impeller, three characteristic frequencies (4.089fn, 2.519fn, and 3.238fn, where fn is the rotational frequency) were confirmed. Analyses revealed that the 4.089fn was due to the periodic shedding of cavitation structures on the suction surfaces at the inducer outlet, 2.519fn was induced by the periodic occurrence and collapse of cavitation on the suction surfaces at the impeller inlet; and 3.238fn was from the periodic shedding of cavitation structures on the suction surfaces at the impeller middle blades. The existence of thermodynamic effects decreased the frequency of cavitation shedding and increased the frequency of the periodic occurrence and collapse of cavitation.
液氧涡轮泵是火箭发动机的重要组成部分。由于热力学因素的影响,涡轮泵中空化流引起的不稳定性受到了广泛的关注。本文对考虑热力学效应的涡轮泵进行了非定常数值模拟。分析了涡轮泵压力波动的频率组成和来源,揭示了有热力学作用和无热力学作用时涡轮泵压力波动的差异。结果表明:压力波动主要是由叶轮与扩散器的相互作用引起的,热力学效应使特征频率的幅值略有增加;此外,在电感器和叶轮中,确定了三个特征频率(4.089fn、2.519fn和3.238fn,其中fn为旋转频率)。分析表明,4.089fn为诱导体出口吸力面空化结构的周期性脱落所致,2.519fn为叶轮进口吸力面空化结构的周期性发生和坍缩所致;3.238fn来源于叶轮中叶吸力面空化结构的周期性脱落。热力学效应的存在降低了空化脱落的频率,增加了空化周期性发生和崩塌的频率。
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引用次数: 11
Analysis of Gas-Liquid-Solid Three-Phase Flows in Hydrocyclones Through a Coupled Method of VOF and DEM 利用VOF和DEM耦合方法分析旋流器内气-液-固三相流动
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-11-01 DOI: 10.1115/1.4051219
Jiachuan Yu, Xiaotong Luo, Bo Wang, Song-hai Wu, Jingtao Wang
Liquid-gas-solid three-phase flows in hydrocyclones are studied numerically in this paper by employing a coupled method of volume of fluid (VOF) and discrete element model (DEM) with RSM turbulence model. The numerical method is validated by comparing the calculated results to those of experiments published in literature about the separation of particle flows in hydrocyclones. Since VOF-DEM model could capture the gas-liquid interface of particle flows, the three-dimensional formation process of the air-core together with the formation of the spiral trajectory of particles are depicted for the first time. In addition, the effects of the particle concentration ? (less than 12%) on the air-core formation time Tf and diameter Da are studied systematically, which has not been reported in literature. The increase of ? has both positive and negative actions on the change of Tf and Da, and compromises of two kinds of actions generate the valley or peak of curves of Tf vs ? and Da vs ?, respectively. Moreover, the results for three hydrocyclones with different cone angles are also compared to study the effects of the cylindrical and conical section on the air-core formation and the separation performance of the hydrocyclones. By analyzing the flow fields and the pressure changes inside the hydrocyclones, qualitative explanations of the relevant discoveries are given in this paper. The results will be helpful in the investigation of the multiphase flow behaviors in the hydrocyclone and in the selection of the appropriate hydrocyclone.
本文采用流体体积(VOF)和离散元模型(DEM)耦合方法,结合RSM湍流模型,对旋流器内液-气-固三相流动进行了数值研究。将数值计算结果与文献中关于旋流器内颗粒流分离的实验结果进行了比较,验证了数值方法的正确性。由于VOF-DEM模型能够捕捉颗粒流的气液界面,因此首次描述了气芯的三维形成过程以及颗粒螺旋轨迹的形成。此外,粒子浓度的影响?(小于12%)对空芯形成时间Tf和直径Da的影响进行了系统的研究,这在文献中没有报道。的增加?对Tf和Da的变化既有正作用,也有负作用,两种作用的折衷产生Tf vs ?和Da vs ?此外,还比较了三种不同锥角旋流器的实验结果,研究了圆柱形和锥形截面对旋流器空芯形成和分离性能的影响。本文通过对旋流器内部流场和压力变化的分析,对相关发现进行了定性解释。研究结果对研究旋流器内的多相流特性和选择合适的旋流器具有一定的指导意义。
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引用次数: 5
Air-Water Flow Properties in Hydraulic Jumps With Fully and Partially Developed Inflow Conditions 完全和部分发展入流条件下液压跃变中的空气-水流动特性
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-10-01 DOI: 10.1115/1.4051199
L. Montano, S. Felder
Novel air–water flow measurements were conducted in fully aerated hydraulic jumps with partially and fully developed supercritical inflow conditions. Irrespective of the inflow conditions, the hydraulic jumps resembled typical flow patterns with strong aeration and instabilities, albeit hydraulic jumps with fully developed inflow conditions had a more upward directed roller motion and a larger clear water core in the second half of the roller. Hydraulic jumps with fully developed inflow conditions had comparatively larger void fractions in the first half of the jump roller and larger bubble count rates throughout, while a comparatively larger number of smaller bubble sizes suggested a stronger break-up of bubbles. This was consistent with slightly larger interfacial velocities and turbulence intensities in the first half of the jump roller with fully developed inflow conditions. An assessment of the required sampling duration for air–water flow properties indicated the requirement to sample for at least five times longer than applied in previous studies. These results highlighted the need to carefully consider the inflow conditions and sampling parameters for aerated hydraulic jumps.
在完全加气的水力跳跃条件下,在部分和完全发展的超临界流入条件下进行了新型的空气-水流量测量。无论入流条件如何,水力跳变都类似于典型的流型,具有强通气和不稳定性,尽管在充分发展的入流条件下,水力跳变具有更多向上定向的滚轮运动,并且在滚轮的后半部分具有更大的清澈水芯。在充分发展的入流条件下,液压跃变在跃变滚轮的前半段具有较大的空隙分数和较大的气泡计数率,而相对较多的小气泡尺寸则表明气泡破碎更强。这与跳跃滚轮前半部分的界面速度和湍流强度略大的情况是一致的,并且流入条件完全发达。对空气-水流动特性所需采样时间的评估表明,需要的采样时间至少比以前的研究长五倍。这些结果强调了需要仔细考虑入流条件和充气液压跳井的采样参数。
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引用次数: 9
Generation of Twin Vortex Rope in the Draft-Tube Elbow of a Francis Turbine During Deep Part-Load Operation 混流式水轮机尾水管弯头深部分负荷运行时双涡绳的产生
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-10-01 DOI: 10.1115/1.4051150
M. H. Khozaei, A. Favrel, T. Masuko, N. Yamaguchi, K. Miyagawa
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引用次数: 8
Flow of Power-Law Fluids Past a Rotating Cylinder at High Reynolds Numbers 幂律流体在高雷诺数下流过旋转圆柱体的流动
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-10-01 DOI: 10.1115/1.4050973
P. Thakur, Naveen Tiwari, R. Chhabra
In this study, a rotating cylinder is placed in a stream of shear-thinning fluids, flowing with a uniform velocity. Detailed investigations are performed for the following range of conditions: Reynolds number 100≤Re≤500, power-law index 0.2≤n≤1 and rotational velocity 0≤α≤5. Flow transitions are observed from steady to unsteady at critical values of the Reynolds number, the rotational velocity, and the power-law index. Critical values of the Reynolds number Rec have been obtained for varying levels of the rotational velocity, and the power-law index. Rec varies nonmonotonically with the rotational velocity. At a particular Reynolds number, an increase of the rotational velocity acts as a vortex suppression technique. For shear-thinning fluids considered here, the vortex suppression occurs at a larger value of the critical rotational velocity αc, relative to Newtonian fluids. For the unsteady flow, the lift coefficient versus time curve exhibits oscillatory behavior, and this has been used to delineate the flow regime as steady or unsteady flow. For unsteady flow regimes, both the amplitude of the lift coefficient and the Strouhal number increase with increasing Reynolds numbers. The results presented in this work for such high Reynolds numbers elucidate the possible complex interplay between the kinematic and rheological parameters of non-Newtonian fluids. This investigation also complements the currently available low Reynolds number results up to ∼ Re=140.
在这项研究中,一个旋转的圆柱体被放置在以匀速流动的剪切变薄流体流中。在雷诺数100≤Re≤500,幂律指数0.2≤n≤1,转速0≤α≤5的条件下进行了详细的研究。在雷诺数、转速和幂律指数的临界值下,观察到流动从定常到非定常的转变。得到了不同转速和幂律指数下雷诺数Rec的临界值。Rec随转速非单调变化。在一定的雷诺数下,增加旋转速度可以起到抑制涡流的作用。对于这里考虑的剪切减薄流体,相对于牛顿流体,在较大的临界转速αc值下发生涡抑制。对于非定常流场,升力系数随时间的变化曲线表现出振荡特性,这一特性被用来描述定常流场或非定常流场。对于非定常流型,升力系数的幅值和斯特罗哈尔数都随雷诺数的增加而增加。在如此高的雷诺数下,本研究的结果阐明了非牛顿流体的运动学和流变参数之间可能存在的复杂相互作用。这项研究还补充了目前可获得的低雷诺数结果,最高可达~ Re=140。
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引用次数: 0
On the Motion of Single and Twin Oblique Particle Clouds in Stagnant Water 单斜粒子云和双斜粒子云在死水中的运动
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-10-01 DOI: 10.1115/1.4051149
Mahsa Janati, A. Azimi
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引用次数: 1
Fluid Dynamics and Pressure Drop Prediction of Two-Phase Flow Through Sudden Contractions 突然收缩两相流的流体动力学和压降预测
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-09-01 DOI: 10.1115/1.4050962
S. Patra, M. K. Roul, P. Satapathy, A. Barik
The aim of the present study is to investigate fluid dynamics and pressure drop across sudden contractions in a two-dimensional, axisymmetric pipe carrying a two-phase mixture of air (secondary phase) and water (primary phase), using the Eulerian–Eulerian model of the multiphase flow physics to solve the mass, momentum, volume fraction and turbulent quantities with relevant boundary conditions in a finite volume framework. The realizable per-phase k-ε and Reynolds stress models have been used as the closure for turbulent quantities along with enhanced wall function for the near-wall treatment. The effects of various parameters such as mass flux, mass flow quality, area ratio (0.056–0.619), flow directions (horizontal/vertical), and system pressure on the two-phase pressure drops due to a contraction in the pipe have been quantified. For both the single and two-phase flows, it has been observed that the pressure drop decreases with area ratio, and increases with mass flux and mass flow quality of two-phase flow. The vena contracta for a single-phase flow was found. But for two-phase flow, neither the vena contracta nor the recirculation zone has been observed, as the mass quality exceeds above 50%. A higher pressure drop has been observed for vertical pipes as compared to horizontal pipes. The present numerical results have also been validated with published experimental results, believed to be one of the alternatives to the costly experimental methods for predicting the flow dynamics and pressure drop.
本研究的目的是研究二维轴对称管道中空气(次级相)和水(初级相)两相混合物的流体动力学和突然收缩时的压降,使用多相流物理学的欧拉-欧拉模型在有限体积框架中求解具有相关边界条件的质量、动量、体积分数和湍流量。采用可实现的每相k-ε和雷诺应力模型作为紊流量的封闭模型,并增强了近壁处理的壁面函数。量化了质量流量、质量流质量、面积比(0.056 ~ 0.619)、流动方向(水平/垂直)、系统压力等参数对管道收缩引起的两相压降的影响。无论是单相流还是两相流,压降都随面积比的增大而减小,随两相流的质量流量和质量流质量的增大而增大。发现了单相流的收缩静脉。但对于两相流,没有观察到静脉收缩和再循环区,质量超过50%以上。与水平管道相比,垂直管道的压降更高。本文的数值计算结果也得到了已发表的实验结果的验证,被认为是替代昂贵的实验方法来预测流动动力学和压降的一种方法。
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引用次数: 3
Investigation of Flow Structure in a Narrow Clearance of a Low Specific Speed Centrifugal Impeller 低比转速离心叶轮窄间隙内流动结构研究
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-08-23 DOI: 10.1115/1.4052240
Yumeno Inaba, Kento Sakai, K. Miyagawa, M. Iino, T. Sano
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引用次数: 0
Effects of Plate Edge Thickness On Droplet Generation Caused by Water Film Breakup At the Plate Edge 平板边缘厚度对平板边缘水膜破裂产生液滴的影响
IF 2 3区 工程技术 Q2 Engineering Pub Date : 2021-08-12 DOI: 10.1115/1.4052126
D. Ito, Susumu Nakano, Yuriko Matsuzaki, Y. Takeda
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引用次数: 0
期刊
Journal of Fluids Engineering-Transactions of the Asme
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