Experimental Thermal and Fluid Science最新文献_第6页

Measurement of dissimilar destruction of turbulent momentum and heat fluxes without instantaneous pressure acquisition 在没有瞬时压力获取的情况下测量湍流动量和热通量的不同破坏

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-22 DOI: 10.1016/j.expthermflusci.2025.111621

Toru Mukai, Mamoru Takahashi, Komei Fujikura, Koichi Tsujimoto, Toshitake Ando

Pressure–rate-of-strain and pressure–temperature-gradient statistically contribute to the destruction of turbulent momentum and heat fluxes, respectively. However, in instantaneous fields, both forward (loss) and backward (gain) destruction events can occur. Moreover, dissimilar destruction of turbulent fluxes, such as the forward destruction of momentum flux and backward destruction of heat flux, and vice versa, can arise in shear flows. In this study, we experimentally quantify the dissimilarity of turbulent fluxes in a heated round jet. The destruction of the turbulent fluxes is governed by the pressure-rate-of-strain for the momentum flux and the pressure-temperature-gradient of the heat flux. To circumvent the need for instantaneous pressure fluctuation measurements, we employed a combined probe consisting of an X-type hot-wire and two parallel cold-wire sensors. This setup enabled the quantification of the fraction of total events corresponding to dissimilar flux destruction. The combined probe provided accurate velocity and temperature statistics, including their derivatives, except in the outer regions of the jet, where the mean velocity is extremely small. Furthermore, confidence in measuring intermediate-scale fluctuations, which are related to the destruction of turbulent fluxes, is confirmed. Finally, the joint statistics between the velocity and temperature derivatives indicate that the destruction of turbulent fluxes in a free round jet is highly dissimilar. We find that the coherence of the destruction of turbulent fluxes due to intermediate-scale fluctuations is at most 0.4 and decreases with the streamwise distance from the exit and increasing frequency. Furthermore, approximately half of the instantaneous events exhibit dissimilar destruction of the turbulent fluxes.

压力-应变速率和压力-温度梯度在统计上分别对湍流动量和热通量的破坏有贡献。然而，在瞬时场中，向前（损失）和向后（增益）破坏事件都可能发生。此外，在剪切流动中，湍流通量的不同破坏，如动量通量的前向破坏和热通量的后向破坏，反之亦然。在本研究中，我们通过实验量化了加热圆形射流中湍流通量的差异性。湍流通量的破坏由动量通量的压力-应变速率和热流通量的压力-温度梯度决定。为了避免瞬时压力波动测量的需要，我们采用了由x型热线和两个平行冷线传感器组成的组合探头。这种设置可以量化与不同通量破坏相对应的总事件的比例。联合探针提供了精确的速度和温度统计数据，包括它们的导数，除了在射流的外部区域，那里的平均速度非常小。此外，还证实了测量与湍流通量破坏有关的中尺度波动的可信度。最后，速度导数和温度导数之间的联合统计表明，自由圆射流中湍流通量的破坏是高度不同的。我们发现，中尺度波动对湍流通量破坏的相干性最大为0.4，并且随着离出口的流向距离和频率的增加而减小。此外，大约一半的瞬时事件表现出不同的湍流通量破坏。

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引用次数: 0

Swirling flow and spray atomization interactions in a swirl cup airblast fuel injector: Venturi outlet angle 旋流杯式喷风喷油器中的旋流与喷雾雾化相互作用：文丘里出口角

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-22 DOI: 10.1016/j.expthermflusci.2025.111622

Yushuai Liu , Chuanyu Fang , Shaolin Wang , Cunxi Liu , Yong Mu , Gang Xu

Swirl cup airblast fuel injectors are critical components in modern low-emission gas turbine combustors. Understanding the underlying physics of the interaction between fuel spray and complex swirling airflow is crucial for optimizing injector performance. This study investigates the influence of Venturi outlet angles (15°, 25°, and 35°) on airflow field and spray atomization dynamics. Advanced optical diagnostics, including high-speed shadowgraph, Phase Doppler Particle Analyzer (PDPA), Particle Imaging Velocimetry (PIV), and Planar Mie scattering (PMie), were employed to quantify flow-spray interactions under controlled fuel flow rates (2.0–4.0 kg/h) and 3 % relative air pressure drop. Results demonstrate that the Venturi outlet angle significantly modulates primary atomization. Increasing the angle from 15° to 35° reduces liquid film length by 69.2 % due to enhanced gas–liquid shear stress. Moreover, larger angles amplify central toroidal recirculation zone (CTRZ) reverse velocity (−1.2 to −6.8 m/s), intensifying droplet entrainment and reducing Sauter Mean Diameter (SMD) by 30.9 %. These findings highlight that Venturi angles > 25° optimize atomization by balancing shear-driven breakup and recirculation-enhanced mixing, providing critical insights for designing fuel injectors with improved combustion stability and emission performance.

旋流杯式鼓风喷油器是现代低排放燃气轮机燃烧室的关键部件。了解燃油喷射与复杂旋转气流之间相互作用的基本物理原理对于优化喷油器性能至关重要。本文研究了文丘里出口角（15°、25°和35°）对气流场和喷雾雾化动力学的影响。采用先进的光学诊断技术，包括高速阴影成像、相位多普勒粒子分析仪（PDPA）、粒子成像测速仪（PIV）和平面米氏散射（PMie），量化控制燃油流量（2.0-4.0 kg/h）和3%相对空气压降下的流动-喷雾相互作用。结果表明，文丘里出口角对一次雾化有明显的调节作用。将夹角从15°增加到35°，由于气液剪切应力的增强，液膜长度减少了69.2%。此外，更大的角度放大了中心环形再循环区（CTRZ）的反向速度（- 1.2 ~ - 6.8 m/s），强化了液滴夹带，使井眼平均直径（SMD）减小了30.9%。这些研究结果表明，文丘里角25°通过平衡剪切驱动的破碎和再循环增强的混合来优化雾化，为设计具有更好燃烧稳定性和排放性能的喷油器提供了重要见解。

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引用次数: 0

Study on the microscopic characteristics of successive droplet clusters impacting on the wall 连续液滴簇撞击壁面的微观特性研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-17 DOI: 10.1016/j.expthermflusci.2025.111619

Feixiang Chang , Mang Yan , Hongliang Luo , Wuli Hong , Yewen Feng , Fei Liu , Chang Zhai , Kang Yang , Bo Song , Jian Zhang , Samir Chandra Ray

In Direct Injection Spark Ignition (DISI) internal combustion engines, fuel droplets inevitably impact the cylinder walls, resulting in droplet adhesion and incomplete combustion, thereby increasing pollutant emissions. The injection strategy has been proven to significantly improve the droplet-wall interaction. Initially, the Refractive Index Matching (RIM) method was used to measure fuel adhesion under both single and double injection conditions, with results confirming that the double injection strategy significantly reduced the fuel adhesion mass. To investigate the mechanisms underlying the reduction in fuel adhesion with double injection, Particle image analysis (PIA) and a multiple droplets producer were employed to examine the micro-behavior of successive droplet clusters near the wall surface. Statistical analyses were conducted on droplet size and velocity. Results showed that, when the two successive droplet clusters impact the wall, the Sauter Mean Diameter (SMD) of the second cluster is greater than that of the first cluster. There are two reasons for this. First, this difference is attributed to the coalescence between the leading droplets of the second droplet cluster and the trailing droplets of the first droplet cluster. Second, when the second droplet cluster impacts the wall, the breakup of fuel adhesion can also lead to the formation of larger droplets. Moreover, the second droplet cluster exhibits a significantly higher penetration velocity than that of the first, which can be attributed to the interaction of the velocity fields between the trailing droplets of the first cluster and the leading droplets of the second cluster. Furthermore, analysis of the average minimum droplet distance shows that droplet number density near the wall is relatively high and decreases with increasing distance from the wall. Lastly, the Bai model was used to predict the probabilities of stick, rebound, spread, and splash of successive droplet clusters at various observation points.

在直喷式火花点火（Direct Injection Spark Ignition， DISI）内燃机中，燃油液滴不可避免地会撞击汽缸壁面，造成液滴粘附，燃烧不完全，从而增加污染物排放。该注入策略已被证明可以显著改善液滴-壁面相互作用。首先，使用折射率匹配（RIM）方法测量了单次和双次喷射条件下的燃油粘附质量，结果证实双次喷射策略显著降低了燃油粘附质量。为了研究双重喷射降低燃油粘附的机制，采用粒子图像分析（PIA）和多液滴产生器对壁面附近连续液滴团的微观行为进行了研究。对液滴大小和速度进行了统计分析。结果表明，当连续两个液滴团撞击壁面时，第二个液滴团的Sauter Mean Diameter （SMD）大于第一个液滴团。这有两个原因。首先，这种差异归因于第二个液滴团的先导液滴和第一个液滴团的尾随液滴之间的聚并。其次，当第二液滴簇撞击壁面时，燃料黏附的破裂也会导致更大液滴的形成。第二液滴团的穿透速度明显高于第一液滴团，这可能是由于第一液滴团尾部液滴与第二液滴团前导液滴之间的速度场相互作用所致。此外，对平均最小液滴距离的分析表明，液滴数密度在壁面附近较高，且随着离壁面距离的增加而减小。最后，利用Bai模型预测了不同观测点连续液滴团的粘附、反弹、扩散和飞溅概率。

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引用次数: 0

Effect of stratification on thermoacoustic instability, emissions, and flame macrostructure in a swirl-stabilized dual annular burner: An experimental study 涡流稳定双环形燃烧器中分层对热声不稳定性、发射和火焰宏观结构的影响：一项实验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-16 DOI: 10.1016/j.expthermflusci.2025.111620

Qazi Talal , Zubairu Abubakar , Ahmed Gaber H. Saif , ELSaeed Saad ELSihy , M. Raghib Shakeel , Esmail M.A. Mokheimer

Stratified flames have attracted significant attention due to their superior resilience to turbulence and enhanced flame stability, enabling reduced NO_x and CO emissions. In this study, an innovative dual annular stratified burner was designed and experimentally investigated to characterize thermoacoustic instability, emissions and flame macrostructure in swirling and non-swirling (jet) methane-air flames. Experiments were systematically conducted across stratification ratios (SR = 1–3) and global equivalence ratios (Φ_g) ranging from lean blowoff to rich conditions (Φ_g = 1.2). Swirling flames exhibited consistently acceptable emissions (NO_x and CO < 20 ppm) under stable lean operating conditions (Φ_g = 0.55–0.8) for all SRs tested. Jet flames showed no thermoacoustic instabilities irrespective of SR or Φ_g variations. Similarly, swirling flames remained stable for Φ_g < 0.8; however, at Φ_g = 0.8, thermoacoustic instability initiated, characterized by coupled oscillations of acoustic pressure and heat release fluctuations. These oscillations were sustained until Φ_g = 1.1, beyond which decoupling occurred. Limit cycle oscillations with heightened sound pressure amplitudes were observed at lower stratification ratios (SR = 1–1.5), whereas no limit cycles were detected at higher SR values (>1.5). Increasing SR significantly suppressed instability amplitudes, notably resulting in a 70 % reduction of oscillation amplitudes at Φ_g = 0.9 when SR increased from 1 to 3. Flame macrostructure analysis confirmed improved anchoring and mixing characteristics of swirling flames compared to jet flames, particularly at higher SR conditions. This work highlights that controlled stratification effectively enhances operational stability and produces more compact flames in swirling combustors, offering valuable insights for developing low-emission and high-efficiency combustion systems.

分层火焰由于其对湍流的优越恢复能力和增强的火焰稳定性而引起了极大的关注，从而减少了氮氧化物和一氧化碳的排放。在这项研究中，设计了一种创新的双环形分层燃烧器，并对其进行了实验研究，以表征旋转和非旋转（射流）甲烷-空气火焰的热声不稳定性、发射和火焰宏观结构。实验系统地进行了分层比（SR = 1-3）和整体等效比（Φg），范围从贫吹到富条件（Φg = 1.2）。在稳定的精益操作条件下（Φg = 0.55-0.8），所有测试的旋转火焰都显示出可接受的排放（NOx和CO <； 20ppm）。射流火焰没有表现出热声不稳定性，与SR或Φg的变化无关。同样，旋转火焰在Φg <； 0.8；然而，当Φg = 0.8时，热声不稳定开始，其特征是声压和热释放波动的耦合振荡。这些振荡一直持续到Φg = 1.1，超过这个时间就发生了解耦。在较低的分层比（SR = 1-1.5）下观察到声压振幅增大的极限环振荡，而在较高的SR值（>1.5）下没有检测到极限环。增加SR可显著抑制不稳定振幅，尤其当SR从1增加到3时，在Φg = 0.9处振荡振幅降低70%。火焰宏观结构分析证实，与喷射火焰相比，旋流火焰的锚定和混合特性有所改善，特别是在高SR条件下。这项工作强调了控制分层有效地提高了旋转燃烧器的运行稳定性，并产生了更紧凑的火焰，为开发低排放和高效的燃烧系统提供了有价值的见解。

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引用次数: 0

An experimental investigation of transient ice accretion process on a high-lift airfoil model for UAV applications 无人机大升力翼型模型瞬态结冰过程的实验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-13 DOI: 10.1016/j.expthermflusci.2025.111612

Manaf Muhammed , Anvesh Dhulipalla , Harsha Sista , Hassan A. Khawaja , Muhammad S. Virk , Hui Hu

An experimental study is performed to investigate the transient ice accretion process along the surface of a high-lift, S1223 airfoil model, and the icing-induced aerodynamic performance degradation. The UAV airfoil model was exposed to typically glaze and rime icing conditions encountered by UAVs flying in low-altitude airspace. While the rime ice accretion was found to conform with the original profile of the UAV airfoil model well in general, substantial “feather-like” ice roughness elements were observed to grow rapidly over both the suction-side and pressure-side surfaces near the airfoil leading edge. The glaze ice accretion process was featured by obvious wind-driven water runback to transport the unfrozen water mass from the airfoil frontal surface to further downstream locations, causing the formation of complex rivulet-shaped ice structures and growth of ice “horns” along the leading edge and “finger-liked icicles” near the trailing edge. The aerodynamic performance of the UAV airfoil was found to degrade continuously with the increasing ice accretion time. The ice accretion over a period of 463 s was found to reduce UAV endurance from 18% to 46 % and diminish the UAV flying range by 13 % to 40 %, depending on the nature of ice accreted. The acquired ice accretion images were coordinated with the aerodynamic force measurements to gain further insight into the underlying physics for a better understanding of the UAV inflight icing phenomena.

通过实验研究了高升力S1223翼型模型表面瞬态结冰过程以及结冰引起的气动性能下降。无人机翼型模型暴露在无人机在低空空域飞行时遇到的典型釉和霜结冰条件下。而时间冰的增加被发现符合无人机翼型模型的原始轮廓很好，在一般情况下，大量的“羽状”冰粗糙度元素被观察到在吸侧和压力侧表面附近翼型前缘迅速增长。釉面结冰过程的特点是明显的风驱动水倒流，将未冻结的水团从翼型前表面输送到更下游的位置，形成复杂的小溪状冰结构，前缘形成冰“角”，后缘附近形成“指状冰柱”。研究发现，随着结冰时间的增加，无人机翼型的气动性能不断下降。在463秒期间的冰的增加被发现减少无人机的续航力从18%到46%并且减少无人机的飞行距离13%到40%，这取决于冰的增加的性质。获取的冰积图像与气动力测量相协调，以进一步了解潜在的物理现象，以便更好地理解无人机飞行结冰现象。

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引用次数: 0

Wake behavior and entrainment motion in the far-field stage of over-tripped boundary layer turbulence 过跳跃式边界层湍流远场阶段的尾迹行为和夹带运动

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-13 DOI: 10.1016/j.expthermflusci.2025.111617

Letian Chen , Zhanqi Tang , Zhenqing Li , Nan Jiang

This study investigates the far-field wake behavior and entrainment motions of the over-tripped boundary layer (OT-BL) turbulence induced by a family of wall-mounted tripwires with different wall blockage rate

σ_{w}

. Friction Reynolds number

{Re}_{τ}

is more than twice that of the unperturbed canonical turbulent boundary layer. Far-field streamwise development of the OT-BL is referred to as a cooperative action of wall-driven and wake-driven mechanisms. Spatial two-point correlation and intermittency factor are employed to quantify the wall-driven and wake-driven ranges. The wall driver shows a weak dependence on the tripwire configuration, whereas the wake driver is clearly related to the tripwire configuration. Along with downstream development, the wake-driven region exhibits an upward and spreading trend, which correlates positively with

σ_{w}

of tripwires. The wake dynamics in turbulent region and near-interface region are revealed from the turbulent/non-turbulent interface perspective. In the upstream stage, the wake is controlled by the tripwire-excited disturbed eddies, and then, in the downstream stage, the near-interface wake dynamics are gradually similar to canonical pattern. Further, entrainment is considered based on nibbling and engulfing motions. For OT-BL, tripwire-excited disturbed eddies enhance nibbling and engulfing entrainment. Nibbling entrainment is the main entrainment mode, although engulfing process is also a significant component. Finally, the study assesses the far-field recovery trend of the OT-BLs’ wake dynamics and entrainment motion. This research provides a reference for tripwire design to simulate higher-

{Re}_{τ}

OT-BL in a finite test section. Meanwhile, we discuss the evaluation scheme on the wake turbulence characteristics of OT-BL from multiple perspectives.

本文研究了不同壁挂绊网堵塞率σw对过绊网边界层（OT-BL）湍流的远场尾迹行为和夹带运动。摩擦雷诺数Reτ是无扰动正则湍流边界层的两倍以上。OT-BL的远场流向发展是壁面驱动和尾迹驱动机制的协同作用。利用空间两点相关和间歇因子对壁面驱动和尾迹驱动范围进行量化。壁面驱动对绊网配置的依赖性较弱，而尾流驱动则明显与绊网配置相关。尾迹驱动区随下游发展呈上升扩展趋势，与绊索σw呈正相关。从湍流/非湍流界面的角度揭示了湍流区和近界面区的尾迹动力学。在上游阶段，尾迹由绊索激发的扰动涡流控制，而在下游阶段，近界面尾迹动力学逐渐向规范模式靠拢。此外，夹带被认为是基于啃咬和吞噬的运动。对于OT-BL，绊索激发扰动涡流增强了啃咬和吞噬夹带。咬食夹带是主要的夹带方式，吞没过程也是一个重要的组成部分。最后，研究评估了OT-BLs尾流动力学和夹带运动的远场恢复趋势。该研究为在有限试验段模拟高reτ OT-BL的绊网设计提供了参考。同时，从多个角度探讨了OT-BL尾流湍流特性的评价方案。

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引用次数: 0

High-speed impact of water droplets on microtextured surfaces: Effect of roughness and wettability on corona splashing 水滴对微纹理表面的高速冲击：粗糙度和润湿性对电晕飞溅的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-11 DOI: 10.1016/j.expthermflusci.2025.111618

Danila Verkhodanov , Nikita Khomutov , Maxim Piskunov , Ivan Vozhakov , Sergey Starinskiy , Alexey Safonov , Nikita Smirnov

A study of the high-speed impact of water droplets on smooth and microtextured fluoropolymer-coated titanium surfaces is presented. The experimental samples had an average roughness R_a from 0.04 μm to 15.4 μm and a static contact angle θ from 74° to 164°. The 0.5–1.3-mm droplets were impacted on the surfaces at velocities U₀ = 5–20 m/s (the Weber number We = 450–2,800). Using a high-speed video camera with a sample rate of 60,000 frames per second, the values of the opening angle α, the maximum diameter D_cor, and the lifetime of the corona were measured and analyzed. In addition, the mean splashing velocities of both large and small secondary fragments were captured. A dimensionless ratio, α/θ, which characterizes the predominance of inertial or adhesive forces, was proposed for the development of an empirical model for predicting D_cor. This model was validated using data from other authors, which proved its applicability in the ranges of We = 450–2,800, R_a = 1.05–38 µm, θ = 69–164° (water) and θ

\approx

0° (ethanol). The research elucidated that superhydrophobic microtextured surfaces provide greater symmetry in corona splash and a larger opening angle. However, these surfaces also delayed liquid removal during splashing, which has the potential to impact the effectiveness of their water-repellent properties.

研究了水滴对光滑和微纹理含氟聚合物涂层钛表面的高速冲击。实验样品的平均粗糙度Ra为0.04 ~ 15.4 μm，静态接触角θ为74 ~ 164°。0.5 ~ 1.3 mm液滴以U0 = 5 ~ 20m /s（韦伯数We = 450 ~ 2800）的速度撞击表面。利用60000帧/ s的高速摄像机，测量和分析了日冕的开启角α、最大直径Dcor和寿命。此外，还获得了大碎片和小碎片的平均飞溅速度。提出了一个无量纲比α/θ，它表征了惯性力或附着力的优势，用于开发预测Dcor的经验模型。该模型在We = 450 ~ 2800, Ra = 1.05 ~ 38µm, θ = 69 ~ 164°（水）和θ≈0°（乙醇）范围内的适用性得到验证。研究表明，超疏水微织构表面提供了更大的电晕飞溅对称性和更大的开口角。然而，这些表面也延迟了飞溅过程中液体的去除，这有可能影响其防水性能的有效性。

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引用次数: 0

Flow and wave characteristics of jet drainage film under crossflow 横流作用下射流疏水膜的流动和波动特性

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-10 DOI: 10.1016/j.expthermflusci.2025.111616

Qiuxiang Chen, Xinying Wang, Qiang Li, Hongfei Hu, Haijun Wang

The interaction between jet drainage films and crossflow is widespread in engineering systems such as liquid rocket engines and nuclear reactor emergency cooling systems. In these processes, an understanding of the flow behavior and fluctuation characteristics of drainage films under crossflow is essential. In this study, an experimental system was constructed to investigate the behavior of jet drainage films under crossflow. The spatial evolution of film offset, average film thickness, base film thickness, wave height, and fluctuation characteristics was investigated under varying crossflow velocities using high-speed imaging and spectral confocal measurement techniques. The results show that the drainage film is shifted to the crossflow direction, and the offset increases linearly with the flow distance, which is inversely proportional to the jet Weber number and directly proportional to the crossflow Weber number. The spatial distribution characteristics of the average liquid film thickness, base film thickness, and wave height are jointly influenced by the jet Weber number and crossflow velocity. The cross-sectional averages of liquid film thickness, base film thickness, and wave height exhibit an initial decrease followed by a subsequent increase with flow distance. The standard deviation of the liquid film thickness was significantly and linearly correlated with its average value, with a slope of approximately 0.3. As the crossflow velocity increases, the liquid film fluctuations on the leeward side of the drainage film are significantly suppressed at low jet Weber numbers, while the liquid film fluctuations on the windward side are notably weakened at the high jet Weber number.

射流排水膜与横流之间的相互作用在液体火箭发动机和核反应堆应急冷却系统等工程系统中广泛存在。在这些过程中，了解排水膜在横流作用下的流动行为和波动特征是至关重要的。在本研究中，建立了一个实验系统来研究横流作用下射流疏水膜的行为。利用高速成像和光谱共聚焦测量技术，研究了不同横流速度下的膜偏移量、平均膜厚、基膜厚度、波高和波动特性的空间演变。结果表明：疏水膜向横流方向偏移，偏移量随流动距离的增加呈线性增加，与射流韦伯数成反比，与横流韦伯数成正比；射流韦伯数和横流速度共同影响平均液膜厚度、基膜厚度和波高的空间分布特征。液膜厚度、基膜厚度和波高的截面平均值随着流动距离的增加呈现先减小后增大的趋势。液膜厚度的标准差与其平均值呈显著线性相关，斜率约为0.3。随着横流速度的增加，低射流韦伯数时疏水膜背风侧液膜波动被显著抑制，高射流韦伯数时迎风侧液膜波动被显著减弱。

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引用次数: 0

Water droplet impact-freezing behaviors on cold superhydrophobic cylindrical surfaces 超疏水圆柱表面水滴的冲击冻结行为

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-07 DOI: 10.1016/j.expthermflusci.2025.111613

Qi Guo , Jiaxiang Zheng , Zunru Fu , Hui Gao , Dongsheng Wen

The impact-freezing behavior of droplets on cold superhydrophobic cylinders was investigated using silica-based coating and a self-constructed low-temperature droplet impact experimental platform. The effects of surface temperature, droplet impact velocity, and surface curvature on droplet dynamics and freezing behavior were systematically investigated. Experimental results revealed that the surface temperature predominantly inhibited droplet retraction, with limited influence on the spreading stage. The effect of surface curvature was found to be more complicated. Droplets tended to freeze rather than rebound at smaller curvature diameters, highlighting the dominance of heat transfer. As the curvature diameter increased, fluid flow effects became more pronounced, leading to a larger circumferential spreading factor. Then, this factor gradually decreased with further increases in diameter and eventually stabilized. Experiment also showed that the circumferential maximum spreading factor was positively correlated with both the surface supercooling degree and the Weber number, but negatively correlated with the curvature diameters ratio. Notably, the influence of surface temperature on impact-freezing was highly related to surface curvature. These findings provided insights into optimizing structured superhydrophobic surfaces for anti-icing performance.

采用硅基涂层和自行搭建的低温液滴撞击实验平台，研究了液滴在超疏水圆筒上的撞击冻结行为。系统地研究了表面温度、液滴撞击速度和表面曲率对液滴动力学和冻结行为的影响。实验结果表明，表面温度主要抑制液滴缩回，对扩散阶段的影响有限。表面曲率的影响更为复杂。液滴倾向于在较小的曲率直径处冻结而不是反弹，这突出了传热的优势。随着曲率直径的增大，流体流动效应更加明显，导致周向扩散系数增大。随着直径的进一步增大，该因子逐渐减小，最终趋于稳定。实验还表明，周向最大扩散系数与表面过冷度和韦伯数呈正相关，与曲率直径比呈负相关。值得注意的是，表面温度对冲击冻结的影响与表面曲率高度相关。这些发现为优化结构超疏水表面的抗冰性能提供了见解。

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引用次数: 0

Interfacial characteristics of a perturbed liquid jet in quiescent air 静空气中扰动液体射流的界面特性

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-04 DOI: 10.1016/j.expthermflusci.2025.111603

Tianyi Wang, Yannis Hardalupas

The physical understanding of liquid jet breakup in quiescent air remains incomplete due to the complex interactions among influencing parameters and limitations in current measurement techniques. In this study, a needle pin was positioned at the nozzle exit of a liquid jet pressure atomiser to introduce an artificial perturbation of controlled magnitude, enabling an investigation on the influence of flow disturbances on the breakup process. This perturbation is introduced to model potential flow disturbances that may occur inside the nozzle of an atomiser, such as liquid flow separation or cavitation. The interfacial characteristics of the liquid jet, including surface morphology and interfacial motion, were analysed to assess the impact of the imposed perturbation on the breakup process. Optical Connectivity (OC), which transmits a laser beam through the intact liquid core, was employed to capture detailed interface geometry. The instantaneous interfacial characteristics were tracked in time using Optical Flow Velocimetry (OFV) to measure the interfacial velocity. Proper Orthogonal Decomposition (POD) was applied to extract the dominant interfacial wave structures, which were subsequently correlated with interfacial motion to provide a comprehensive assessment of the perturbation effects. The consistency between the dominant interfacial geometry extracted from POD and the measured interfacial velocity further validates the reliability of the OC-OFV technique. The findings reveal that introducing artificial perturbations and adjusting their amplitude can alter the interfacial motion and geometry of the liquid jet by modifying internal flow patterns, which in turn influence the liquid breakup process and the velocity of the resulting liquid fragments. This highlights the significant impact of nozzle disturbances, such as cavitation or manufacturing defects, on atomisation performance. Moreover, the results suggest that applying controlled artificial perturbations could serve as an effective strategy for controlling the breakup process and optimising the resulting spray droplet velocity.

由于影响参数之间复杂的相互作用和现有测量技术的局限性，对静止空气中液体射流破裂的物理认识仍然不完整。在本研究中，在液体射流压力喷雾器的喷嘴出口处放置一个针脚，以引入一个可控量级的人工扰动，从而研究流动扰动对破裂过程的影响。引入这种扰动来模拟可能发生在喷雾器喷嘴内部的潜在流动扰动，例如液体流动分离或空化。分析了液体射流的界面特征，包括表面形貌和界面运动，以评估施加的扰动对破裂过程的影响。光学连通性（OC）通过完整的液体核心传输激光束，用于捕获详细的界面几何形状。利用光流测速仪（OFV）测量界面速度，及时跟踪界面的瞬时特性。应用适当正交分解（POD）提取界面波的优势结构，并将其与界面运动进行关联，从而对扰动效应进行综合评价。从POD中提取的优势界面几何形状与实测界面速度之间的一致性进一步验证了OC-OFV技术的可靠性。研究结果表明，引入人工扰动并调节其振幅可以通过改变内部流动模式来改变液体射流的界面运动和几何形状，从而影响液体破碎过程和产生的液体碎片的速度。这突出了喷嘴干扰（如空化或制造缺陷）对雾化性能的重大影响。此外，研究结果表明，施加可控的人工扰动可以作为控制破碎过程和优化最终雾滴速度的有效策略。

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