European Journal of Mechanics B-fluids最新文献_第3页

Natural convection heat transfer and intensification for a discrete heat source in a vertical annulus 垂直环形空间中离散热源的自然对流传热与强化

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-15 DOI: 10.1016/j.euromechflu.2024.10.011

John Njoroge, Puzhen Gao

The decay heat removal in advanced nuclear power plants encourages the use of natural convection cooling as a precaution during power outages. The ongoing designs of micro nuclear reactors institute an ambient air-cooled system via natural convection, which points to a localized heat source cooling in an open loop. The analyses presented in this paper address the problem of natural convection heat transfer of a heat source placed in an open-ended annular channel. Numerical simulations were carried out for various heat source lengths, moved along the inner cylinder of the annulus. Using the transition SST turbulence model, the influence of the annular gap size on heat transfer rates was investigated by adjusting the radius ratios between 3 and 5, while heat transfer enhancement was achieved by way of longitudinal fins. Results of heat transfer rates, local heat transfer characteristics, and mass flow rates are presented. The change in elevation of the heat source at L_c/b > 2.7 in the open system did not have a profound influence as indicated by the Rayleigh number buoyancy parameter and Nusselt numbers. However, the annular gap size was unequivocally the most influential geometrical parameter. Additionally, the average Nusselt numbers at any unfinned heated section length were adequately described by the correlation Nu_L = 0.959Nu_H(L/H)^0.855, for

0 < L / H < 1

. The number of fins and the fin height were the most important parameters for the finned system where case-specific gains of more than 50 % in average Nusselt number were obtained. The results of the present analyses provide invaluable information for the development of passively cooled systems utilizing ambient air.

先进核电站的衰变散热鼓励使用自然对流冷却，作为停电期间的预防措施。目前正在设计的微型核反应堆采用了通过自然对流进行环境空气冷却的系统，这表明局部热源冷却是一个开放式循环。本文分析了放置在开口环形通道中的热源的自然对流传热问题。针对沿环形内筒移动的各种热源长度进行了数值模拟。利用过渡 SST 湍流模型，通过调整 3 至 5 之间的半径比，研究了环形间隙大小对传热速率的影响，同时通过纵向鳍片实现了传热增强。结果显示了传热速率、局部传热特性和质量流量。从雷利数浮力参数和努塞尔特数可以看出，开放系统中 Lc/b > 2.7 处热源高度的变化并没有产生深远的影响。然而，环形间隙的大小无疑是影响最大的几何参数。此外，对于 0<L/H<1，NuL = 0.959NuH(L/H)0.855（相关系数）可以充分描述任何非翅片加热段长度下的平均努塞尔特数。翅片数量和翅片高度是翅片系统最重要的参数，平均努塞尔特数的具体增益超过 50%。本分析结果为开发利用环境空气的被动冷却系统提供了宝贵的信息。

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引用次数: 0

Hydrodynamic force coefficients for spherical triangle shell fragments: Dependence on the aspect ratio and flatness 球形三角壳碎片的流体动力系数：取决于长宽比和平面度

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-15 DOI: 10.1016/j.euromechflu.2024.10.006

Ian G.B. Adams , Julian Simeonov , Carley Walker

Euler–Lagrange simulations of particle-laden flow require hydrodynamic models of drag and lift forces for individual particles. Our goal is to develop models that can prescribe these forces for arbitrarily orientated shell objects. Here, we use computational fluid dynamics simulations of steady bottom-boundary layer flow over a series of spherical triangle shell fragments to calculate the hydrodynamic forces. The simulations explicitly resolve the wall boundary layers using grid resolution on the order of

y_{+} = 1

at the shell fragment surface and use the SST k-omega turbulence closure model. These fragments cover a range of aspect ratio and flatness characteristics. The shell fragments are generated as triangular selections of a spherical shell with azimuthal and longitudinal angles proscribed based on elongation and flatness parameters (varying between 1 to 5, and 0.02 to 0.2 respectively), while characteristic length of the fragment is held constant to define the overall fragment size. Fragment orientations are considered with independently varying pitch, roll, and yaw each ranging from 0 to 180 degrees. The numerical estimates for the forces from all simulations were used to develop robust parameterizations of the drag and lift as a function of aspect ratio and flatness characteristics, as well as orientation of the shell fragments.

载颗粒流的欧拉-拉格朗日模拟需要单个颗粒的阻力和升力的流体力学模型。我们的目标是开发能够为任意方向的壳体物体规定这些力的模型。在这里，我们利用计算流体动力学模拟一系列球形三角形壳体碎片上稳定的底部边界层流动，来计算流体动力。模拟明确解析了壳体碎片表面的壁边界层，网格分辨率为 y+=1，并使用 SST k-omega 湍流闭合模型。这些片段涵盖了一系列长宽比和平面度特征。生成的壳碎片是球壳的三角形选区，其方位角和纵向角根据伸长率和平整度参数（分别在 1 到 5 和 0.02 到 0.2 之间变化）进行限制，而碎片的特征长度保持不变，以定义整体碎片大小。片段方向考虑了独立变化的俯仰、滚动和偏航，每个方向的变化范围为 0 至 180 度。所有模拟的力的数值估计值都被用来开发阻力和升力的稳健参数，作为长宽比、平整度特征以及壳碎片方向的函数。

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引用次数: 0

Benchmark experimental study on cavitating flow around Clark-Y 11.7 % hydrofoil at various angles of attack under controlled levels of dissolved air 克拉克-Y 11.7%水翼在不同攻角、受控溶气水平下的气蚀流基准实验研究

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-11 DOI: 10.1016/j.euromechflu.2024.10.007

Emad Hasani Malekshah , Włodzimierz Wróblewski , Mirosław Majkut

The present research aims to study cavitating flow around a CLARK-Y 11.7 % hydrofoil with variable angles of attack (α) while maintaining controlled levels of dissolved air in the operating fluid, which is water. A series of experiments were conducted using a water tunnel facility, where the cavitation characteristics were measured and observed using sensors and high-speed imaging techniques. The variables studied in the present work are cavitation number (1 ≤ σ ≤ 2.2) and angle of attack (α = 4°, 6°, 8°, 10°, and 12°), with dissolved air levels (DAL) in the range of 9.3 ppm to 13.1 ppm. The dimensionless cavity length decreases significantly with increasing values of σ/α, indicating an inverse relationship where higher cavitation numbers or lower angles of attack result in shorter cavities. The cavity length follows a power-law scaling relationship, with the empirical equation

L_{\max} / C = 4.78 \times {(σ / α)}^{- 0.76}

.Increasing the angle of attack transitions the cavitation nature from stable (Mode I) to dynamic (Mode II) and highly oscillating (Mode III). Larger cavities result in lower Strouhal numbers, which indicates reduced vortex shedding activity. The relationship between the Strouhal number and the normalized cavitation number σ/α is characterized by the power-law equation

St = 0.041 \times {(σ / α)}^{0.3}

. The pressure coefficient at the leading-edge increases with the angle of attack at low cavitation numbers, while higher cavitation numbers lead to greater pressure coefficient differences between the leading and trailing edges.

The present study offers an extensive dataset and empirical correlations that may serve as a benchmark framework, which facilitates the validation of computational and experimental models of cavitating flow under similar conditions.

本研究旨在研究具有可变攻角 (α) 的 CLARK-Y 11.7 % 水翼周围的空化流，同时保持工作流体（水）中可控的溶解空气水平。利用水隧道设施进行了一系列实验，使用传感器和高速成像技术对空化特性进行了测量和观察。本次研究的变量为空化数（1 ≤ σ ≤ 2.2）和攻角（α = 4°、6°、8°、10°和 12°），溶解空气含量（DAL）范围为 9.3 ppm 至 13.1 ppm。无量纲空腔长度随着 σ/α 值的增加而显著减小，这表明存在一种反比关系，即空化数越高或攻击角越小，空腔越短。空腔长度遵循幂律缩放关系，经验公式为 Lmax/C=4.78×σ/α-0.76 。增加攻角可将空化性质从稳定（模式 I）转变为动态（模式 II）和高度振荡（模式 III）。空腔越大，斯特劳哈尔数越低，这表明涡流脱落活动越少。斯特劳哈尔数与归一化空化数 σ/α 之间的关系用幂律方程 St=0.041×σ/α0.3 表示。本研究提供了广泛的数据集和经验相关性，可作为基准框架，便于验证类似条件下气蚀流的计算和实验模型。

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引用次数: 0

Gravity wave interaction with compressive VLFS in the presence of thick porous bed 厚多孔床存在时重力波与压缩 VLFS 的相互作用

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-11 DOI: 10.1016/j.euromechflu.2024.10.003

Saniya Suhail , Koushik Kanti Barman , Sunanda Saha , Chia-Cheng Tsai

The present study deals with the problem of oblique wave scattering by a finite floating elastic plate over a thick porous bed. A potential flow-coupled thin-elastic plate model has been developed, and the wave flow model resembling the physical scenario is framed into a boundary value problem (BVP). A semi-analytical method has been employed to obtain the hydrodynamic coefficients following the numerical and physical illustrations by varying different geometrical parameters. Prior to wave interaction, dispersive roots are thoroughly analyzed, and a critical frequency is observed above which the group velocity is negative. Within this range, minimum reflection and maximum transmission occur due to the high porosity of the seabed. A discontinuous pattern in the reflection coefficient is observed within the blocking range, which mainly exists for high compression. The findings of this work may be highly valuable for Very Large Floating Structures in marine settings, particularly in situations where interactions are primarily influenced by the thick porous beds.

本研究涉及厚多孔床面有限浮动弹性板对斜波的散射问题。研究建立了一个势流耦合薄弹性板模型，并将类似物理情景的波流模型框定为一个边界值问题（BVP）。采用半解析方法，通过改变不同的几何参数，按照数值和物理图解获得流体力学系数。在波浪相互作用之前，对色散根进行了彻底分析，并观察到一个临界频率，在该频率之上，群速度为负值。在这一范围内，由于海底孔隙率较高，反射系数最小，透射系数最大。在阻塞范围内，反射系数出现了不连续的模式，主要存在于高压缩的情况下。这项工作的发现对于海洋环境中的超大型浮动结构可能非常有价值，尤其是在相互作用主要受厚多孔海床影响的情况下。

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引用次数: 0

A Study on the interaction of shock tube-generated blast waves with a circular object at different pressure ratios 关于冲击管产生的爆炸波在不同压力比下与圆形物体相互作用的研究

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-07 DOI: 10.1016/j.euromechflu.2024.10.001

Abhishek Kundu , Murugan Thangadurai

The interaction of high peak overpressure blast waves with a circular object placed at two different axial locations from the shock tube exit is studied through numerical simulation using an in-house developed multi-component Navier–Stokes solver. The driver and driven sections of the shock tube were 0.8 m and 6 m, respectively. Helium is used in the driver section, while atmospheric air is used in the driven section and outside the shock tube. The evolution of blast waves inside an open-ended shock tube and its interaction with a rectangular object is reported in Murugan et al.. (2022). Here, the blast wave interacting with a circular object is examined for diaphragm pressure ratios of 13 and 57 by placing the objects at 250 mm and 500 mm from the shock tube exit. The flow field is evaluated through numerical Schlieren, vorticity, density, pressure plots, and the enstrophy plot, which shows the vortical structures that originated in the flow field. The blast load acting on the circular object is calculated for two diaphragm pressure ratios and axial locations. This study helps understand the reflection and diffraction of blast waves and associated flow fields around circular objects used in blast wave attenuation.

通过使用内部开发的多分量纳维-斯托克斯求解器进行数值模拟，研究了峰值超压冲击波与位于冲击管出口两个不同轴向位置的圆形物体之间的相互作用。冲击管的驱动部分和从动部分分别为 0.8 米和 6 米。驱动部分使用的是氦气，而从动部分和冲击管外部使用的是大气空气。Murugan 等人报告了开口式冲击管内爆炸波的演变及其与矩形物体的相互作用（2022 年）。(2022).在此，通过将物体放置在距离冲击管出口 250 毫米和 500 毫米的位置，研究了在膜片压力比为 13 和 57 时，冲击波与圆形物体的相互作用。流场通过数值 Schlieren、涡度、密度、压力图和 enstrophy 图进行评估，enstrophy 图显示了源自流场的涡旋结构。针对两种隔膜压力比和轴向位置，计算了作用在圆形物体上的爆炸载荷。这项研究有助于了解爆炸波的反射和衍射以及用于爆炸波衰减的圆形物体周围的相关流场。

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引用次数: 0

Adjusting Manning coefficients to simulate tsunami propagation over porous coral reef 调整曼宁系数以模拟海啸在多孔珊瑚礁上的传播

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-10-02 DOI: 10.1016/j.euromechflu.2024.09.006

Adrien Poupardin , Philippe Heinrich

This study investigates the effect of porous coral reef on the tsunami propagation in terms of experimental and numerical modelling. It aims at quantifying the influence of several input parameters on the wave attenuation and at adjusting Manning coefficients to reproduce experimental results. The density and the surface of individual reefs are fixed as well as the width and length of the coral barrier. Results show that the reef height is the most sensitive parameter. This latter affects the tsunami propagation with an attenuation of the first wave reaching 15 % compared to the case with a smooth reef. Wave breaking occurs on the reef flat for each test but, as expected, its location depends greatly on the reservoir depths difference. Numerical simulations show that the Manning coefficient must be adjusted both by considering the coral reef height and the spatial grid resolution. It varies from 0.01 (for lowest reef with highest grid resolution) to 0.058 (for higher reefs with coarsest grid resolution).

本研究从实验和数值模拟两个方面研究了多孔珊瑚礁对海啸传播的影响。研究旨在量化几个输入参数对波浪衰减的影响，并调整曼宁系数以重现实验结果。各个珊瑚礁的密度和表面以及珊瑚屏障的宽度和长度都是固定的。结果表明，珊瑚礁高度是最敏感的参数。后者影响海啸的传播，与光滑珊瑚礁相比，第一波的衰减达到 15%。在每次试验中，破浪都发生在礁石平地上，但正如预期的那样，其位置在很大程度上取决于水库深度差。数值模拟表明，曼宁系数必须根据珊瑚礁高度和空间网格分辨率进行调整。它从 0.01（网格分辨率最高的最低珊瑚礁）到 0.058（网格分辨率最粗的较高珊瑚礁）不等。

引用次数: 0

Parametric study of traveling wave motion in energy absorption mode 能量吸收模式下的行波运动参数研究

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-09-26 DOI: 10.1016/j.euromechflu.2024.09.005

Zhifei Cui , Mingliang Qi , Qiyu Ma , Diangui Huang

There are two modes of traveling wave motion, traveling wave propulsion and traveling wave energy absorption. In this paper, a two-dimensional flexible traveling wave plate is taken as the research object. The characteristic length and characteristic parameter of traveling wave motion are determined by numerical simulation, and the parametric study of the traveling wave motion in energy absorption mode is conducted. The effects of dimensionless amplitude and dimensionless wave velocity on the energy absorption characteristics of flexible traveling wave plate are analyzed, and the mechanism of traveling wave energy absorption is revealed. The results show that the larger the dimensionless amplitude is, the stronger the work capacity of the traveling wave plate becomes, while the absolute amplitude or absolute wavelength has little effect on the work capacity of the traveling wave plate. Under different waveforms, the work capacity of the traveling wave plate increases first and then decreases as the dimensionless wave velocity increases. Within the parameter range studied in this article, when the dimensionless amplitude is 0.2 and the dimensionless wave velocity is 0.5, the traveling wave plate can achieve an energy absorption efficiency of about 40 %.

行波运动有两种模式，即行波推进和行波能量吸收。本文以二维柔性行波板为研究对象。通过数值模拟确定了行波运动的特征长度和特征参数，并对能量吸收模式下的行波运动进行了参数化研究。分析了无量纲振幅和无量纲波速对柔性行波板能量吸收特性的影响，揭示了行波能量吸收的机理。结果表明，无量纲振幅越大，行波板的做功能力越强，而绝对振幅或绝对波长对行波板的做功能力影响不大。在不同的波形下，随着无量纲波速的增大，行波板的做功能力先增大后减小。在本文研究的参数范围内，当无量纲振幅为 0.2、无量纲波速为 0.5 时，行波板的能量吸收效率约为 40%。

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引用次数: 0

Asymmetric vertical transport in weakly forced shallow flows 弱强迫浅层流中的非对称垂直输运

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-09-24 DOI: 10.1016/j.euromechflu.2024.09.004

L.M. Flores Ramírez, L.P.J. Kamp, H.J.H. Clercx, M. Duran-Matute

In this paper, we report on an investigation of the vertical transport of tracer particles released within a shallow, continuously-forced flow by means of numerical simulations. The investigation is motivated by the shallow flows encountered in many environmental situations and inspired by the laboratory experiments conducted in electromagnetically forced shallow fluid layers. The flow is confined to a thin fluid layer by stress-free top and no-slip bottom walls. The dynamics and the transport properties of the shallow flow are investigated under various flow conditions characterized by a Reynolds number related to the forcing,

R e_{F}

, and the aspect ratio of vertical and horizontal length scales

δ

. The forcing generates an array of vortices that becomes unsteady when

R e_{F} δ^{2} ≳ 10

. These vortices are accompanied by upwellings in their cores which are surrounded by narrower, stronger downwellings. Hence, upwellings occur where the horizontal flow is vorticity-dominated, while downwellings where it is strain-dominated. The magnitude of the asymmetry in strength and size of the vertical flows and their correlation with horizontal structures depends on the flow conditions and significantly influences the vertical spreading of particles within the fluid volume. Under conditions leading to a large asymmetry, particles within updrafts are transported slowly upwards, while particles within downdrafts rapidly move downwards. In addition, particles are trapped for longer within the updrafts than downdrafts because of their correlation with vorticity-dominated regions. However, when the flow becomes fully three-dimensional and highly unsteady for large

R e_{F} δ^{2}

values, this transport asymmetry subsides because the updrafts and downdrafts exhibit similar strength and size in such flow conditions. Consequently, similar amounts of particles are transported upwards and downwards at similar rates.

在本文中，我们报告了通过数值模拟对浅层连续强制流内释放的示踪粒子的垂直传输进行的研究。这项研究的动机是在许多环境条件下遇到的浅层流动，并受到在电磁强迫浅层流体层中进行的实验室实验的启发。流动被限制在无应力顶壁和无滑动底壁的薄流体层中。研究了各种流动条件下浅层流的动力学和传输特性，这些流动条件的特征是与强迫有关的雷诺数 ReF 以及垂直和水平长度尺度的纵横比 δ。强迫产生了一系列涡流，当 ReFδ2≳10 时，涡流变得不稳定。这些漩涡的核心部分伴随着上升气流，周围是较窄、较强的下沉气流。因此，在水平气流以涡度为主的地方会出现上升气流，而在水平气流以应变为主的地方则会出现下降气流。垂直流的强度和大小的不对称程度及其与水平结构的相关性取决于流动条件，并对流体体积内颗粒的垂直扩散产生重大影响。在导致较大不对称性的条件下，上升气流中的颗粒会缓慢向上移动，而下降气流中的颗粒则会迅速向下移动。此外，由于上升气流与涡度主导区域相关，颗粒在上升气流中的滞留时间比在下降气流中长。然而，当气流变得完全三维且高度不稳定（ReFδ2 值较大）时，这种传输不对称现象就会消失，因为在这种气流条件下，上升气流和下降气流表现出相似的强度和大小。因此，相似数量的颗粒会以相似的速度向上和向下输送。

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引用次数: 0

Influence of radiation on the stability of MHD micropolar fluid in a vertical channel 辐射对垂直通道中 MHD 微极性流体稳定性的影响

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-09-18 DOI: 10.1016/j.euromechflu.2024.09.003

Pankaj Barman, Darbhasayanam Srinivasacharya

The objective of the present article is to explore the stability of micropolar fluid flow in a vertical channel in the presence of thermal radiation and a transverse magnetic field. The generalized eigenvalue problem is numerically solved by utilizing the Chebyshev spectral collocation method, which is obtained from the perturbed state using the normal mode technique. The numerical data were compared with previously published results for particular cases. The critical modified Grashof number ( $G r_{c}^{'}$ ) and the associated wave numbers ( $α_{c}$ ) are calculated and displayed graphically for different values of the parameters. It is noticed that the boundaries of instability may be increased or decreased with the flow governing parameters because of the presence of a magnetic field and thermal radiation.

本文旨在探讨存在热辐射和横向磁场时垂直通道中微极性流体流动的稳定性。利用切比雪夫频谱配位法对广义特征值问题进行了数值求解，该方法是利用法模技术从扰动状态得到的。数值数据与之前公布的特定情况下的结果进行了比较。计算了临界修正格拉肖夫数（Grc′）和相关波数（αc），并以图形显示了不同参数值。我们注意到，由于磁场和热辐射的存在，不稳定性的边界可能会随着流动调节参数的变化而增大或减小。

引用次数: 0

Settling velocity of weakly inertial particles in vertical flow 垂直流中弱惯性粒子的沉降速度

IF 2.5 3区工程技术 Q2 MECHANICS

European Journal of Mechanics B-fluids

Pub Date : 2024-09-12 DOI: 10.1016/j.euromechflu.2024.09.001

Seungjun Baek , Yong Sung Park , Il Won Seo

We investigate the settling velocity change of weakly inertial particles, whose density ratio to fluid ranges from 1.35 to 1.38, in vertical water flow. To assess the effect of turbulence, we experimentally examine the dependence of modifications of velocity on physical scales, including time, velocity, and length, between particles and turbulence. It is observed that the settling velocity is either enhanced or hindered by the turbulence compared to stagnant conditions. The change in settling velocity is observed to be responsive to both the inertia of particles and the turbulence intensity. In cases of weak turbulence or with larger particles, the settling velocity exhibits small changes and even decreases. Conversely, the change in settling velocity is more pronounced for smaller particles and in more intense turbulence, reaching a maximum increase at

S t \approx O (1 0^{- 3})

. We compare our experimental results with existing studies conducted in solid–liquid two-phase flow, finding a consistent tendency. In both prior research and the present study, the length scale parameter,

S t S v

, has consistently been important in discerning inertial conditions that determine the change in settling velocity under turbulent conditions.

我们研究了弱惯性颗粒在垂直水流中的沉降速度变化，这些颗粒与流体的密度比在 1.35 到 1.38 之间。为了评估湍流的影响，我们通过实验研究了颗粒和湍流之间的速度变化对物理尺度（包括时间、速度和长度）的依赖性。与停滞条件相比，湍流会增强或阻碍沉降速度。沉降速度的变化与颗粒的惯性和湍流强度有关。在湍流较弱或颗粒较大的情况下，沉降速度的变化很小，甚至会减小。相反，对于较小的颗粒和较强的湍流，沉降速度的变化更为明显，在 St≈O(10-3) 时达到最大增幅。我们将实验结果与现有的固液两相流研究结果进行了比较，发现了一致的趋势。在之前的研究和本研究中，长度尺度参数 StSv 在辨别决定湍流条件下沉降速度变化的惯性条件方面一直很重要。

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引用次数: 0