Experimental Thermal and Fluid Science最新文献_第2页

Heat transfer mechanism of vortex structure evolution in dual synthetic jets over a heating plate 加热板上双合成射流涡结构演变的传热机理

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2026-01-05 DOI: 10.1016/j.expthermflusci.2026.111689

Yuanyuan Liu, Xinyu Liang, Wenqiang Peng, Zhenbing Luo, Xinyu Xie, Xiong Deng

Multiple-orifice synthetic jets have garnered significant attention in recent research due to their exceptional heat transfer performance in small installations. To achieve a larger heat dissipation area while minimizing installation height, this study employs dual synthetic jets impinging on a heated plate and investigates the influence of installation height (h_i/w_o) on the heat transfer characteristics. The heat transfer mechanisms associated with vortex structure evolution are analyzed using particle image velocimetry (PIV) and an infrared camera, thereby facilitating a deeper understanding of flow-thermal coupling behavior. It was found that h_i/w_o significantly alters the evolution of vortex structures at a nearly constant jet Reynolds number (Re_j ≈ 1600). The optimal heat transfer performance (Nu_max ≈ 136) was achieved at h_i/w_o = 2–3, balancing the unsteady benefit and near-wall flow enhancement. At this installation height, the inner primary vortex (IPV) rolls up moderately and partially merges its vorticity with the wall shear layer (WSL), while secondary vortices (SVs), SV-1 and SV-2, emanate from the outer primary vortex (OPV). The appropriate vorticity distributions of SV-1 and SV-2 promote the entrainment of ambient fluid and fluctuate the WSL. The spectral analysis further substantiates the presence of unsteady benefit. Both Welch spectra and Spectral POD mode confirmed that h_i/w_o = 2–3 delivers the best coherence maintenance, indicating an overall optimal benefit from heat transfer. Conversely, an insufficient installation height (h_i/w_o = 0–1) mitigated IPV roll-up. Although higher momentum flux and periodic kinetic energy were attained near the orifice, the convective heat transfer coefficient decayed rapidly. Excessive installation height (h_i/w_o = 4) allowed complete IPV roll-up. IPV breaks down into secondary vortices before merging into the WSL, resulting in deteriorated heat transfer performance.

在最近的研究中，由于多孔合成射流在小型装置中具有出色的传热性能，因此引起了人们的极大关注。为了在最小化安装高度的同时获得更大的散热面积，本研究采用双合成射流冲击加热板，研究安装高度（hi/wo）对传热特性的影响。利用粒子图像测速（PIV）和红外相机分析了与涡结构演变相关的传热机制，从而有助于更深入地了解流-热耦合行为。研究发现，在近似恒定的射流雷诺数（Rej≈1600）下，hi/wo显著改变了涡结构的演化。在hi/wo = 2-3时，获得了最佳换热性能（Numax≈136），平衡了非定常效益和近壁面流动增强。在该安装高度，内主涡（IPV）适度卷起并与壁面剪切层（WSL）部分合并，次涡（sv） SV-1和SV-2由外主涡（OPV）发出。SV-1和SV-2适当的涡度分布促进了周围流体的夹带，使WSL波动。谱分析进一步证实了非定常效益的存在。韦尔奇光谱和光谱POD模式都证实，hi/wo = 2-3提供了最佳的相干维持，表明传热的整体最佳效益。相反，安装高度不足（hi/wo = 0-1）会减少IPV的上卷。虽然在孔口附近获得了较高的动量通量和周期动能，但对流换热系数衰减很快。过高的安装高度（hi/wo = 4）允许完全卷起IPV。IPV在合并到WSL之前分解成二次涡，导致换热性能恶化。

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引用次数: 0

Experimental ‘In-situ’ Bayesian Active Learning: Sampling flow fields with a purpose 实验“原位”贝叶斯主动学习：有目的的采样流场

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-29 DOI: 10.1016/j.expthermflusci.2025.111688

Gonçalo G. Cruz , Xavier Ottavy , Fabrizio Fontaneto

Accurately characterizing complex flow fields often requires dense measurement grids. This paper presents an active learning methodology that enables efficient and targeted flow field characterization by dynamically guiding the selection of measurement locations while sampling the flow fields. The approach leverages a Gaussian Process model to represent the flow field and its uncertainty, while the Maximize Expected Prediction Error (MEPE) acquisition function balances exploration of undersampled high uncertainty regions with exploitation in areas of potential error. The active learning methodology is validated on the engineering relevant test case of the ECL5 Ultra-High Bypass Ratio (UHBR) fan, using experimental data acquired at the outlet measurement plane. The results demonstrate that the active learning approach can accurately capture all relevant flow features, including the hub corner separation and wake structures, using only 400 measurements, which is half the number of measurements that were sampled in traditional reference tests. This reduction in measurement effort resulted in a time saving of approximately one hour compared to the three-hour reference data acquisition. Furthermore, the methodology offers researchers flexibility in customizing the data acquisition process to their specific goals through the selection of appropriate stopping criteria. By strategically combining uncertainty and error thresholds, the active learning process can be adapted to achieve a desired balance between measurement effort, accuracy, and uncertainty levels. These findings highlight the possibilities of active learning to significantly enhance the efficiency and cost-effectiveness of experimental fluid mechanics research.

准确表征复杂流场往往需要密集的测量网格。本文提出了一种主动学习方法，通过在流场采样时动态指导测量位置的选择，实现高效和有针对性的流场表征。该方法利用高斯过程模型来表示流场及其不确定性，而最大期望预测误差（MEPE）获取函数平衡了对欠采样高不确定性区域的探索和对潜在误差区域的开发。在ECL5超高涵道比（UHBR）风机的工程相关测试用例上，利用出口测量平面采集的实验数据对主动学习方法进行了验证。结果表明，主动学习方法可以准确捕获所有相关的流动特征，包括轮毂角分离和尾迹结构，仅使用400次测量，这是传统参考测试中采样测量次数的一半。与3小时参考数据采集相比，测量工作量的减少节省了大约1小时的时间。此外，该方法通过选择适当的停止标准，为研究人员提供了定制数据采集过程的灵活性。通过战略性地结合不确定性和错误阈值，主动学习过程可以适应于在测量工作量、准确性和不确定性水平之间实现所需的平衡。这些发现突出了主动学习显著提高实验流体力学研究效率和成本效益的可能性。

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引用次数: 0

Intermittent two-phase flow characterization using advanced diagnostics in a high-pressure large-diameter slightly upward inclined pipe 采用先进的诊断技术对高压大直径微向上倾斜管道中的间歇两相流进行表征

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-21 DOI: 10.1016/j.expthermflusci.2025.111683

Ahmed Aql , E. Al-Safran , E. Pereyra , C. Sarica

This study experimentally investigates slug flow characteristics under high-pressure conditions of 2.76 MPa (400 psi) in a 2° upward-inclined, large ID pipe with an internal diameter of 156 mm (6.1 in.), using advanced diagnostic instruments, including high-resolution wire-mesh sensors and a high-speed visualization system. The tests are performed within a broad range of superficial liquid and gas velocities of v_SL = 0.01–0.35 m/s, and v_SG = 1.3–2.5 m/s, allowing investigation of operational and topological features, such as film reversal and interfacial roughness, and enabling the distinction between slug and pseudo-slug flow. It is found that the strength of the hydraulic seal in the flow structure (slug and pseudo-slug) body governs the characteristics of the intermittent flow. In addition, the superficial liquid velocity v_SL is found to be the major contributor to the formation and stability of the hydraulic seal, followed by the superficial gas velocity v_SG. Specifically, the mean slug length, L_S, and slug frequency, f_S, are significantly influenced by superficial liquid velocity. For example, increasing v_SL promotes longer and more frequent slugs, while the impact of superficial gas velocity on slug flow characteristics depends on the structure body liquid holdup, and hydraulic seal integrity. Overall, superficial gas velocity predominantly decreases liquid holdup in slug and film regions, due to high interfacial shear stress and film thinning.

本研究通过实验研究了在2.76 MPa （400 psi）高压条件下，在2°上斜、内径为156 mm （6.1 in）的大内径管道中，使用先进的诊断仪器，包括高分辨率金属丝网传感器和高速可视化系统的段塞流特性。测试在宽范围内进行，表面液体和气体速度vSL = 0.01-0.35 m/s, vSG = 1.3-2.5 m/s，允许研究操作和拓扑特征，如膜反转和界面粗糙度，并能够区分段塞流和伪段塞流。研究发现，流动结构（段塞和伪段塞）体中液压密封的强度决定了间歇流动的特性。此外，液面流速vSL是影响液压密封形成和稳定的主要因素，其次是气面流速vSG。具体来说，平均段塞长度LS和段塞频率fS受到表面液体速度的显著影响。例如，增加vSL会增加段塞流的时间和频率，而表面气体速度对段塞流特性的影响取决于结构体的含液率和液压密封的完整性。总的来说，由于高界面剪切应力和膜变薄，表面气速主要降低了段塞段和膜区域的液含率。

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引用次数: 0

Dancing vapor clouds above evaporating sessile droplets: Insights from parabolic flight microgravity experiments 在蒸发的液滴上跳舞的蒸汽云：来自抛物线飞行微重力实验的见解

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-18 DOI: 10.1016/j.expthermflusci.2025.111687

Senthil Kumar Parimalanathan , Hatim Machrafi , Adam Chafai , Alexey Rednikov , Pierre Colinet

Evaporation of a sessile droplet is studied in a parabolic flight campaign. The setup elements are similar to some past or planned microgravity experiments in space: pure refrigerant Hydrofluoroether (HFE)-7100 for the liquid, droplet pinning at a 2 mm radius microgroove, nearly normal conditions. The droplet is injected onto a flat substrate through a small central outlet up to a volume between

\sim 6 μ

L and

10 μ

L (contact angles from

\sim 4 5^{\circ}

to 70°) at the beginning of each ‘parabola’ (microgravity period lasting up to

\sim

20 s). Although an unfortunate ‘parasitic post-injection’ (persisting after the pump is off, a quite typical anomaly in microgravity) might have interfered with evaporation-rate measurements, such gaps are bridged using digital holographic vapor interferometry and axisymmetric simulations. Thus, we find that evaporation rates are significantly affected by residual gravity fluctuations in the plane (‘g-jitter’,

\sim 1 0^{- 2}

g here). Quite accordingly, vapor clouds ‘dancing’ following the g-jitter are interferometrically disclosed, in good agreement with simulations. All this provides a noteworthy example of a possible difference between parabolic-flight experiments and those at other platforms (such as sounding rockets) approaching 0 g more precisely. The simulations reveal an independence with respect to high-frequency g-jitter sampling but highlight that each parabola is unique, with its own g-jitter signature. A detailed benchmark analysis is carried out motivated by the question of why the evaporation rates are appreciably higher for periods of negative (upward) g-jitter compared to positive (downward) ones. This is partly related to thermal Marangoni convection, concurrent or not to g-jitter buoyancy convection.

研究了无底液滴在抛物飞行过程中的蒸发。设置元素类似于过去或计划中的一些太空微重力实验：纯制冷剂氢氟醚(HFE)-7100为液体，液滴钉在半径2毫米的微槽上，几乎正常的条件。在每次“抛物线”开始时（微重力持续时间为~ 20秒），将液滴通过一个小的中央出口注射到平面基底上，其体积在~ 6μL到10μL之间（接触角从~ 45°到70°）。尽管不幸的“寄生后注入”（在泵关闭后持续存在，这是微重力下非常典型的异常）可能会干扰蒸发率的测量，但使用数字全息蒸汽干涉测量和轴对称模拟可以弥补这种差距。因此，我们发现蒸发速率受到平面上剩余重力波动（“g抖动”，这里为10−2g）的显著影响。因此，蒸汽云在g抖动后“跳舞”的干涉测量显示，与模拟结果很好地一致。所有这些都提供了一个值得注意的例子，说明抛物线飞行实验与在其他平台（如探空火箭）上更精确地接近0 g的实验之间可能存在的差异。模拟揭示了高频g抖动采样的独立性，但强调每个抛物线都是独特的，具有自己的g抖动特征。为什么负（向上）g抖动时期的蒸发速率明显高于正（向下）g抖动时期，这一问题激发了详细的基准分析。这部分与热马兰戈尼对流有关，是否与g抖动浮力对流有关。

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引用次数: 0

Experimental study on flow pattern transition on horizontal flat tubes with large height-width ratio 大高宽比水平平板管内流型转换的实验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-16 DOI: 10.1016/j.expthermflusci.2025.111686

Wenjie Deng , Zhenhua Quan , Yaohua Zhao , Chunduo Song , Lincheng Wang

The flow pattern between tubes significantly influences the liquid film distribution and flow state on the lower tube bundle in the falling film evaporator, and its transition behavior is critical to the heat transfer performance of the equipment. This study develops a visualization platform to examine flow pattern transitions between horizontal flat tubes with large height-width ratio, utilizing ethylene glycol, ethanol, and water as working fluids. The findings reveal that ethylene glycol exhibits the lowest critical Reynolds number (Re_c), while ethanol shows a more distinct and clearer gas–liquid interface morphology. The Re_c for flow pattern transition increases with higher spray height (H), inlet liquid temperature (T_in), and circulating water temperature (T_cir), with T_in showing the most substantial impact. Flow hysteresis manifests in flow pattern transitions and strengthens with increasing H, T_in and T_cir, with water displaying the most pronounced effect. Based on experimental data, an empirical correlation and flow pattern map better suited for flow pattern transition on horizontal flat tubes is developed, with a maximum relative root mean square error of 12.76%. Research demonstrates that horizontal flat tubes show a lower Re_c for transition to sheet flow compared with horizontal tubes, indicating superior liquid film flow performance. This investigation advances the understanding of flow pattern transition mechanisms on horizontal flat tubes, providing theoretical and experimental foundations for the structural optimization and efficient operation of falling film evaporators.

降膜蒸发器管内的管间流态对下管束的液膜分布和流动状态有重要影响，其过渡行为对降膜蒸发器的传热性能至关重要。本研究开发了一个可视化平台，以乙二醇、乙醇和水为工质，研究大高宽比水平扁平管之间的流型转换。结果表明，乙二醇具有最低的临界雷诺数（Rec），而乙醇具有更清晰的气液界面形态。喷淋高度(H)、进口液温度（Tin）和循环水温度（Tcir）越高，流型转变的Rec越高，其中Tin的影响最大。随着H、Tin和Tcir的增加，流动滞后表现为流型转变，并增强，其中水的影响最为明显。在实验数据的基础上，建立了更适合于水平平面管流型转换的经验相关图和流型图，最大相对均方根误差为12.76%。研究表明，与水平管相比，水平平板管向板流过渡的Rec更低，表明了更优越的液膜流动性能。该研究促进了对水平平板管流型转换机理的认识，为降膜蒸发器的结构优化和高效运行提供了理论和实验依据。

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引用次数: 0

Effect of confinement geometry on pool boiling performance of gold-coated copper surface 约束几何对镀金铜表面池沸性能的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-15 DOI: 10.1016/j.expthermflusci.2025.111685

Gregor Bahč, Armin Hadžić, Matic Može, Matevž Zupančič, Iztok Golobič

Pool boiling is widely employed in compact thermal management systems, but its performance can deteriorate significantly under geometric confinement. This study investigates the combined effects of vertical gap height and confinement plate diameter on pool boiling of distilled water at atmospheric pressure using gold-coated copper samples. The vertical gap between the boiling surface and an overhead plate varied from 0.1λ to 20λ, where λ = 2.5 mm is the capillary length of water, and three plate diameters were examined: 14 mm, 24 mm, and 39 mm. For large gaps (k_gap ≥ 2.5), the critical heat flux (CHF) remained at approximately 1100 kW m⁻² and the heat transfer coefficient (HTC) was comparable to unconfined boiling. As the gap decreases below 2.5λ, both CHF and HTC decrease sharply. At the smallest gap (0.1λ), CHF and HTC were reduced by up to 78 % and 85 %, respectively, relative to the unconfined reference. In the intermediate gap range (0.5λ–2.5λ), the plate diameter had a pronounced effect, with the largest plate producing substantially lower CHF and HTC than the smallest plate for the same gap height due to more restricted radial vapor escape. High-speed visualization confirmed that strong confinement promotes bubble coalescence, vapor accumulation beneath the plate, and intermittent dryout of the boiling surface. Based on the CHF data for all gap heights and plate diameters, empirical correlations were developed using a dimensionless gap ratio and a characteristic plate-size parameter, providing a predictive framework for assessing CHF under combined vertical gap height and confinement plate diameter.

池沸腾被广泛应用于紧凑型热管理系统，但其性能在几何约束下会显著恶化。以镀金铜为实验对象，研究了垂直间隙高度和约束板直径对常压蒸馏水沸腾池的影响。沸点表面与顶板之间的垂直间隙从0.1λ到20λ不等，其中λ = 2.5 mm为水的毛细长度，并检测了三种板的直径：14mm， 24mm和39mm。对于大间隙（kgap≥2.5），临界热流密度（CHF）保持在1100 kW m−2左右，传热系数（HTC）与无侧限沸腾相当。当间隙减小到2.5λ以下时，CHF和HTC都急剧下降。在最小的间隙（0.1λ）， CHF和HTC分别减少高达78%和85%，相对于无限制参考。在中间间隙范围内（0.5λ-2.5λ），极板直径对CHF和HTC的影响显著，在相同间隙高度下，最大极板产生的CHF和HTC明显低于最小极板，因为径向蒸汽逸出受到更大的限制。高速可视化证实，强约束促进了气泡合并，蒸汽在板下积聚，以及沸腾表面的间歇性干燥。基于所有间隙高度和板直径的CHF数据，利用无量纲间隙比和特征板尺寸参数建立了经验相关性，为评估垂直间隙高度和约束板直径联合作用下的CHF提供了预测框架。

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引用次数: 0

Splashing of impacting droplets on an artificial superhydrophobic surface: Effect of viscosity in hole-nucleation process 冲击液滴在人工超疏水表面的飞溅：孔洞成核过程中粘度的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-15 DOI: 10.1016/j.expthermflusci.2025.111682

Kumar Gaurav , Visakh Vaikuntanathan , Sivakumar Deivandren

The present study reports an experimental investigation on splashing of liquid droplets impacting on an artificial superhydrophobic (SHP) surface prepared by coating NeverWet hydrophobic solution. The prepared SHP surface exhibits micro-bumps decorated with nano-structures, as seen in Scanning Electron Microscopy (SEM) images and surface profilometry. The presence of micro-bumps causes the fragmentation of spreading lamella via hole-nucleation process, leading to a significant reduction in droplet contact time as shown in a recent study reported in the literature. The focus of the current study is on the effect of droplet viscosity on the hole-nucleation and contact time of impacting droplets. The experiments with droplet impact velocity,

U_{o}

ranging from 0.3 m/s to 3.6 m/s are conducted using three different droplet liquids – water (W), 20% glycerine and 80% water (G20), and 50% glycerine and 50% water (G50) – varying mainly in their dynamic viscosity. From high-speed videos of droplet impact dynamics, the various impact regimes are first identified and mapped in

W e

(droplet Weber number) –

R e

(droplet Reynolds number) plane for all three droplet liquids. Quantitative measurements of the temporal variation of lamella diameter, number of holes formed, time at which the first hole nucleates, critical impact velocity at which the hole-nucleation begins, and contact time are extracted. These measurements clearly show that the contact time reduction of splashing droplets decreases with increase in droplet viscosity. Moreover, the number of holes formed in the lamella film scales with the number of micro-bumps underneath the droplet at its maximum spreading which, in turn, decreases with increase in droplet viscosity. The time instant at which the first hole nucleates on the lamella film is seen to be independent of the droplet viscosity. A modified model is proposed to describe the effects of droplet viscosity and surface micro-characteristics (height and pitch of surface micro-bumps) on the critical velocity for hole nucleation,

U_{c, h}

. The predictions from this modified model seem to explain the experimental observations on

U_{c, h}

in the current study as well as in the literature.

本文报道了用NeverWet疏水溶液涂覆制备的人工超疏水（SHP）表面上液滴溅射影响的实验研究。从扫描电子显微镜（SEM）图像和表面轮廓分析中可以看出，制备的SHP表面呈现出纳米结构装饰的微凸起。最近文献报道的一项研究表明，微凸起的存在导致通过孔成核过程扩展的片层破碎，导致液滴接触时间显着减少。目前研究的重点是液滴粘度对冲击液滴孔形核和接触时间的影响。液滴冲击速度Uo范围为0.3 m/s ~ 3.6 m/s，实验采用三种不同的液滴液体——水(W)、20%甘油和80%水（G20）、50%甘油和50%水（G50）——主要改变的是它们的动态粘度。从液滴撞击动力学的高速视频中，首先确定了三种液滴液体的不同撞击状态，并在We（液滴韦伯数）- Re（液滴雷诺数）平面上进行了映射。提取了片层直径的时间变化、形成的孔数、第一个孔成核的时间、孔开始成核的临界冲击速度和接触时间的定量测量结果。这些测量清楚地表明，随着液滴粘度的增加，溅射液滴的接触时间减少量减小。此外，在液滴最大扩散时，微凸点的数量随着液滴下方微凸点的数量而增加，而微凸点的数量则随着液滴粘度的增加而减少。第一个孔在片层膜上成核的时间瞬间与液滴粘度无关。提出了一个改进的模型来描述液滴粘度和表面微特征（表面微凸起的高度和节距）对孔成核临界速度Uc，h的影响。这个修正模型的预测似乎可以解释当前研究和文献中对Uc，h的实验观察结果。

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引用次数: 0

Consecutive water entries of two side-by-side spheres: cavity interference and surface closure characteristics 两个并排球体的连续入水：空腔干涉和表面闭合特征

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-13 DOI: 10.1016/j.expthermflusci.2025.111684

Xu Wang , Xujian Lyu , Hui Tang , Chao Qi , Ruisheng Sun

This paper presents an experimental investigation into cavity interference and surface closure characteristics of two side-by-side spheres undergoing consecutive water entries. A high-speed imaging system was employed to capture the dynamic processes of the two cavities, including the cavity elongation and their interaction with the free surface during the closure stage. Four distinct interference modes—rebound, expansion, tail, and bubble-dominated—are found primarily depending on the time interval between the two water entries,

Δ

t, while showing little sensitivity to the lateral distance. Unlike the single-cavity closure, the following cavity, subject to interference, undergoes two separate detachment events from the free surface, characterized by a closure angle (defined as the acute angle between the cavity tail-end face and the free surface) whose magnitude and orientation scale with

Δ

t. Statistical analysis indicates that the initial detachment time is independent of the adjacent cavity’s evolution, whereas the emergence of a closure angle significantly prolongs the complete detachment time and increases cavity length, especially at smaller lateral distances.

本文对两个相邻球体连续进水时的空腔干涉和表面闭合特性进行了实验研究。利用高速成像系统捕捉了两个空腔的动态过程，包括空腔的延伸及其在闭合阶段与自由表面的相互作用。四种不同的干涉模式——回弹、膨胀、尾部和气泡主导——主要取决于两次进水之间的时间间隔Δt，而对侧向距离的敏感性很小。与单腔封闭不同，受干涉影响的下腔从自由面分离两次，其特征为封闭角（定义为腔尾端面与自由面之间的锐角），其大小和方向以Δt表示。统计分析表明，初始脱离时间与邻近空腔的演变无关，而闭合角的出现显著延长了完全脱离时间，增加了空腔长度，特别是在较小的横向距离上。

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引用次数: 0

Dynamics of bursting droplets from surfacing bubble plumes 表面气泡羽流中破裂液滴的动力学

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-12 DOI: 10.1016/j.expthermflusci.2025.111680

Jitae Do , Binbin Wang

The dynamics of bursting droplets from surface bubbles is an important mechanism for water-to-air transport of small particles and contaminants. We investigated bubble-bursting droplets from bubble plumes, released from an air stone (AS) or a single nozzle (SN) at four gas flow rates ranging from 0.1 to 0.8 L min⁻¹. Quantitative imaging was used to analyze the statistics of size and velocity distributions for rising bubbles and droplets ejected by bursting bubbles. Significantly greater droplet number, mass flow rate, and median size were observed in AS, by factors of 20, 8.6, and 1.8 compared to SN, reflecting the influence of subsurface bubble characteristics on droplet production. Log-normal distributions fit well to droplet size and velocity distribution regardless of the release mechanism. The characteristic median sizes show a bubble–droplet relationship of

R_{d} \sim R_{b}^{1.4}

, which implies Bond number relationship of

B o_{d} \sim B o_{b}^{1.4}

under constant fluid properties. Scaling analysis using visco-capillary length and capillary velocity shows

L a_{d} \sim C a_{d}^{- 1.4}

, suggesting a universal scaling relationship for bursting droplets from surfacing of single bubble and bubble plumes. Involving both length and velocity scales of bubbles and droplets shows

F r_{d} \sim {(B o_{b} W e_{b})}^{- 0.3}

, a scaling relationship potentially used for predicting droplet dynamics from bursting bubble plumes. These findings provide the first quantitative scaling linking bubble plume and bursting droplet dynamics, with potential applications in aerosol generation, wastewater aeration, and ocean–atmosphere mass-exchange studies.

表面气泡破裂液滴的动力学是小颗粒和污染物从水到空气传输的重要机制。我们研究了气泡柱中的气泡破裂液滴，从气石（AS）或单喷嘴（SN）中以0.1至0.8 L min - 1的四种气体流速释放。利用定量成像技术对气泡上升和气泡破裂喷射出的液滴的大小和速度分布进行统计分析。与SN相比，AS的液滴数量、质量流量和中位数尺寸分别是20倍、8.6倍和1.8倍，这反映了地下气泡特性对液滴产生的影响。无论释放机制如何，对数正态分布都能很好地适应液滴大小和速度分布。特征中值尺寸表现为Rd ~ Rb1.4的气泡-液滴关系，这意味着恒定流体性质下Bod ~ Bob1.4的键数关系。用粘度-毛细长度和毛细速度进行的结垢分析显示Lad ~ Cad−1.4，表明单泡表面和泡柱表面的破裂液滴具有普遍的结垢关系。涉及气泡和液滴的长度和速度尺度显示为Frd ~ (BobWeb)−0.3，这一尺度关系可能用于预测气泡羽流破裂时的液滴动力学。这些发现首次提供了气泡羽流和破裂液滴动力学之间的定量尺度联系，在气溶胶产生、废水曝气和海洋-大气质量交换研究中具有潜在的应用前景。

{"title":"Dynamics of bursting droplets from surfacing bubble plumes","authors":"Jitae Do , Binbin Wang","doi":"10.1016/j.expthermflusci.2025.111680","DOIUrl":"10.1016/j.expthermflusci.2025.111680","url":null,"abstract":"<div><div>The dynamics of bursting droplets from surface bubbles is an important mechanism for water-to-air transport of small particles and contaminants. We investigated bubble-bursting droplets from bubble plumes, released from an air stone (AS) or a single nozzle (SN) at four gas flow rates ranging from 0.1 to 0.8 L min<sup>−1</sup>. Quantitative imaging was used to analyze the statistics of size and velocity distributions for rising bubbles and droplets ejected by bursting bubbles. Significantly greater droplet number, mass flow rate, and median size were observed in AS, by factors of 20, 8.6, and 1.8 compared to SN, reflecting the influence of subsurface bubble characteristics on droplet production. Log-normal distributions fit well to droplet size and velocity distribution regardless of the release mechanism. The characteristic median sizes show a bubble–droplet relationship of <span><math><mrow><msub><mrow><mi>R</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>∼</mo><msubsup><mrow><mi>R</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>1</mn><mo>.</mo><mn>4</mn></mrow></msubsup></mrow></math></span>, which implies Bond number relationship of <span><math><mrow><mi>B</mi><msub><mrow><mi>o</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>∼</mo><mi>B</mi><msubsup><mrow><mi>o</mi></mrow><mrow><mi>b</mi></mrow><mrow><mn>1</mn><mo>.</mo><mn>4</mn></mrow></msubsup></mrow></math></span> under constant fluid properties. Scaling analysis using visco-capillary length and capillary velocity shows <span><math><mrow><mi>L</mi><msub><mrow><mi>a</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>∼</mo><mi>C</mi><msubsup><mrow><mi>a</mi></mrow><mrow><mi>d</mi></mrow><mrow><mo>−</mo><mn>1</mn><mo>.</mo><mn>4</mn></mrow></msubsup></mrow></math></span>, suggesting a universal scaling relationship for bursting droplets from surfacing of single bubble and bubble plumes. Involving both length and velocity scales of bubbles and droplets shows <span><math><mrow><mi>F</mi><msub><mrow><mi>r</mi></mrow><mrow><mi>d</mi></mrow></msub><mo>∼</mo><msup><mrow><mrow><mo>(</mo><mi>B</mi><msub><mrow><mi>o</mi></mrow><mrow><mi>b</mi></mrow></msub><mi>W</mi><msub><mrow><mi>e</mi></mrow><mrow><mi>b</mi></mrow></msub><mo>)</mo></mrow></mrow><mrow><mo>−</mo><mn>0</mn><mo>.</mo><mn>3</mn></mrow></msup></mrow></math></span>, a scaling relationship potentially used for predicting droplet dynamics from bursting bubble plumes. These findings provide the first quantitative scaling linking bubble plume and bursting droplet dynamics, with potential applications in aerosol generation, wastewater aeration, and ocean–atmosphere mass-exchange studies.</div></div>","PeriodicalId":12294,"journal":{"name":"Experimental Thermal and Fluid Science","volume":"173 ","pages":"Article 111680"},"PeriodicalIF":3.3,"publicationDate":"2025-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145797532","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 0

Vortex dynamics of novel whale-biomimetic and conventional wings: Influence of aspect ratio on tip and fragmented flow structures 新型仿鲸翼和传统翼涡动力学：展弦比对翼尖和破碎流结构的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-12-09 DOI: 10.1016/j.expthermflusci.2025.111681

Halil Hakan Açıkel , Sinem Keskin , Mustafa Serdar Genç , Mustafa Özden , Eren Anıl Sezer , Mehmet Sincar , Muhammer Ayvazoğlu , Rumeysa Şahin

The interaction of the tip vortex and the fragmented vortex on novel humpback whale-biomimetic wings with different low aspect ratios and their effects on aerodynamic performance are presented in this study. A baseline NACA 0015 airfoil and a modified configuration were tested at a chord-based Reynolds number of 0.975 × 10⁴ for different aspect ratios (AR = 1, 2, 3, and infinite). The oil flow visualisation and force measurements were used to explore the effects of the tubercle modification on flow topology, unsteady flow, stall mechanisms, and fluid–structure interactions. Moreover, time-dependent force results were served for spectrogram analysis, which was presented first in this study, to reveal flow modes occurring. The results demonstrate that the whale-inspired geometry alters the laminar separation bubble dynamics by fragmenting large coherent structures into smaller three-dimensional bubbles, which are less susceptible to tip vortex interactions. Time-resolved lift measurements and spectrogram analyses showed that the whale-inspired leading-edge fragmented laminar separation bubbles into smaller, higher-momentum structures, generating higher-frequency flow (fragmented laminar separation bubble-induced and whale flow interaction-induced) modes that mitigated coherent vortex shedding. In AR2, AR3, and 2D wings, two dominant modes emerged. This can be attributed to the intensification of leading-edge vortices interacting with the whale structure, with an increasing aspect ratio. The modified wings exhibited enhanced lift coefficient and delayed stall, particularly for higher aspect ratios, where a mild stall replaced abrupt stall in baseline wings. However, at post-stall conditions, the lift force exhibited higher fluctuation-based stability index values for the whale wings, indicating that while the modification improved overall aerodynamic performance, it slightly reduced flow stability. While studies in the literature have shown that high aspect ratio whale wings provide significant aerodynamic enhancement, particularly at high angles of attack, this study observed that this effect is accompanied by increased vibration due to small, fragmented vortices. Increased vibration is likely to lead to stability issues.

研究了不同低展弦比的新型座头鲸仿生机翼上尖端涡和碎片涡的相互作用及其对气动性能的影响。基线NACA 0015翼型和修改的配置进行了测试，在0.975 × 104的弦为基础的雷诺数为不同的展弦比（AR = 1,2,3，和无限）。利用油流可视化和力测量来探索结核修饰对流动拓扑、非定常流动、失速机制和流固耦合的影响。此外，时间相关的力结果用于谱图分析，这是本研究中首次提出的，以揭示发生的流动模式。结果表明，受鲸鱼启发的几何结构通过将大型连贯结构破碎成较小的三维气泡来改变层流分离气泡动力学，这些气泡不太容易受到尖端涡相互作用的影响。时间分辨升力测量和频谱图分析表明，鲸鱼启发的前缘破碎层流分离气泡变成了更小、更高动量的结构，产生了更高频的流动模式（破碎层流分离气泡诱导和鲸鱼流动相互作用诱导），减轻了相干涡脱落。在AR2、AR3和2D机翼中，出现了两种主要模式。这可以归因于前缘涡与鲸鱼结构相互作用的增强，随着展弦比的增加。改进后的机翼表现出增强的升力系数和延迟失速，特别是在高展弦比下，温和失速取代了基线机翼的突然失速。然而，在失速后条件下，鲸鱼翅膀的升力表现出更高的基于波动的稳定性指数值，这表明尽管改进提高了整体气动性能，但却略微降低了流动稳定性。虽然文献中的研究表明，高展弦比的鲸鱼翅膀提供了显著的空气动力学增强，特别是在大攻角时，但本研究发现，这种效果伴随着由于小而破碎的涡流而增加的振动。增加的振动可能会导致稳定性问题。

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引用次数: 0