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

Nanofluids mixed convection, heat transfer characteristics and effects of volume concentrations in the thermally developing region 纳米流体混合对流、传热特性及热发育区体积浓度的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-21 DOI: 10.1016/j.expthermflusci.2025.111626

Ibrahim Umar Ibrahim , Mohsen Sharifpur , Josua P. Meyer

The vast majority of research on nanofluids only focuses on the heat transfer enhancement and pressure drop characteristics of these fluids. But apart from that, there are other intricate and complex phenomena that are very critical to the understanding of these fluid’s characteristics. The effects of free convection, entrance effects, and the influence of volume concentration on boundary conditions (i.e., laminar start and end, transition and turbulence) were often neglected. This limits our knowledge of these fluids. These phenomena were critical to understanding and fully utilising nanofluid potentials. Therefore, this research experimentally investigated the force and mixed convection of Al₂O₃ − MWCNT/water hybrid nanofluids. Three different concentrations of 0.30, 0.20, and 0.10 were prepared using the two-step method. Results show that an increase in volume concentration significantly affects nanofluid transition boundaries. Because critical Reynolds numbers for all the volume concentrations varied significantly, results show that critical Reynolds numbers of 0.3, 0.2 and 0.1 vol concentrations are Recr_. = 2140, 2200, and 2330, respectively. Thermal entrance influences were found to decrease with the increase in volume concentration. Mixed convection effects were increased with a decrease in volume concentration. Results also revealed that the Nusselt number of 0.3 vol concentration at Re = 1000 was enhanced by about 50 % within the thermal entrance length. In contrast, it was enhanced by about 48.84 % due to mixed convection. It was concluded that heat transfer enhancement was much better due to thermal entrance effects than with mixed convection. Also, the fluid viscosity depends on transition region boundaries, thermal entrance effects, and mixed convection heat transfer characteristics. Also, their characteristics often differ at different axial positions.

绝大多数关于纳米流体的研究只集中在纳米流体的强化传热和压降特性上。但除此之外，还有其他错综复杂的现象对理解这些流体的特性至关重要。自由对流、入口效应和体积浓度对边界条件（即层流开始和结束、过渡和湍流）的影响往往被忽略。这限制了我们对这些液体的了解。这些现象对于理解和充分利用纳米流体电位至关重要。因此，本研究通过实验研究了Al2O3 - MWCNT/水混合纳米流体的作用力和混合对流。采用两步法制备了0.30、0.20和0.10三种不同浓度。结果表明，体积浓度的增加显著影响纳米流体的过渡边界。由于不同体积浓度下的临界雷诺数变化很大，结果表明，0.3、0.2和0.1体积浓度下的临界雷诺数是最小的。= 2140、2200和2330。热入口的影响随着体积浓度的增加而减小。混合对流效应随体积浓度的降低而增强。结果还表明，在Re = 1000时，0.3 vol浓度的努塞尔数在热入口长度范围内提高了约50%。相比之下，混合对流使其增强约48.84%。结果表明，热入口效应比混合对流强化传热效果更好。此外，流体粘度取决于过渡区边界、热入口效应和混合对流换热特性。此外，在不同的轴向位置，它们的特性往往不同。

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引用次数: 0

Dynamic behavior of surface frosting and droplet impact on the frosting superhydrophobic surface 表面结霜的动力学行为及液滴对结霜超疏水表面的影响

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-18 DOI: 10.1016/j.expthermflusci.2025.111634

Bin Ding , Ren-tao He , Wen-hao Song , Zhi-qiang Gong , Jie Zhou , Hao Feng

Although superhydrophobic surfaces have the ability to delay the growth of frost crystals, they still cannot completely prevent frosting at low-temperature environments, which in turn affects the dynamic behavior of droplet impacts on frosting surfaces. Here, the frosting behavior of superhydrophobic surfaces and the dynamic behavior of droplet impact on frosting surfaces were explored through visualization experiments. Firstly, the frost formation behavior of hydrophilic and superhydrophobic surfaces under different humidity conditions was investigated, and the influence of surface wettability and relative humidity on the surface frosting characteristics were analyzed. Then, the dynamic behavior of droplet impacts on frosting superhydrophobic surfaces was studied. And the differences in the dynamic behavior of droplet impacts on supercooled surfaces and frosting superhydrophobic surfaces were compared and analyzed. Finally, the influence of impact velocity on the dynamic behavior of droplet impact frosting superhydrophobic surfaces was explored. The results show that an increase in impact velocity would prolong the duration of the spreading stage, and the processes of droplet retraction, rebound and separation are all completely inhibited with the surfaces temperature decreases. The findings provide experimental evidence for revealing the physical mechanism of the interaction between droplets and frosting superhydrophobic surfaces, which is of great significance for promoting the application of superhydrophobic anti-frosting materials in the industrial field.

虽然超疏水表面具有延缓霜晶生长的能力，但仍不能完全防止低温环境下的结霜，从而影响液滴撞击结霜表面的动态行为。通过可视化实验，研究了超疏水表面的结霜行为和液滴撞击结霜表面的动力学行为。首先，研究了不同湿度条件下亲水性和超疏水性表面的结霜行为，分析了表面润湿性和相对湿度对表面结霜特性的影响。然后，研究了液滴在结霜超疏水表面上的动力学行为。对比分析了液滴在过冷表面和结霜超疏水表面上撞击动力学行为的差异。最后，探讨了冲击速度对液滴冲击磨砂超疏水表面动力学行为的影响。结果表明：随着冲击速度的增加，扩散阶段的持续时间延长，液滴的缩回、回弹和分离过程都随着表面温度的降低而被完全抑制；研究结果为揭示液滴与结霜超疏水表面相互作用的物理机制提供了实验依据，对促进超疏水防霜材料在工业领域的应用具有重要意义。

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引用次数: 0

Mixing and entrainment of liquid fuel in a cavity-based scramjet model combustor 基于空腔的超燃冲压发动机模型燃烧室中液体燃料的混合与夹带

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-17 DOI: 10.1016/j.expthermflusci.2025.111629

Joel van der Lee, Weronika Senior-Tybora, Rudy Kaner, Yuval Aldema-Tshuva, Dan Michaels, Joseph K. Lefkowitz

This work quantitatively investigates liquid fuel mixing and entrainment in a cavity-based scramjet model combustor, focusing on potential and limitations of using an infrared imaging-based measurement technique. The proposed approach produces time-averaged path density maps that enable characterization of fuel distribution in a high-enthalpy supersonic crossflow. Using this method, a total of seven strut-assisted fueling strategies is systematically evaluated at a constant fuel mass flowrate. The discussion of measurement results addresses both the observed distribution maps and profiles, and their interpretation based on known physical processes of supersonic jet breakup, plume evolution, and crossflow interaction. The gained insights reveal key factors to fueling strategy design, such as jet penetration depth and orifice placement along the strut and injector location relative to the cavity. A series of combustion experiments were conducted to evaluate the flame holding characteristics of the injection strategies, allowing the mixing results, expressed in path-integrated fuel density, to be contextualized in terms of stabilization performance of the combustor. While path density is less intuitive, its proportionality between cases enables positioning within the stabilization envelope. In addition, the path density is a useful quantity for direct comparison to numerical modeling efforts. Together, these findings highlight the utility of infrared imaging to study mixing trends for guiding the design of advanced liquid fueling schemes in supersonic combustors.

本研究对基于空腔的超燃冲压发动机模型燃烧室中的液体燃料混合和夹带进行了定量研究，重点研究了基于红外成像的测量技术的潜力和局限性。所提出的方法产生了时间平均路径密度图，可以表征高焓超音速横流中的燃料分布。利用该方法，对恒定燃料质量流量下的7种支柱辅助加油策略进行了系统评价。对测量结果的讨论包括观测到的分布图和剖面，以及基于已知的超音速射流破裂、羽流演化和横流相互作用物理过程的解释。获得的见解揭示了加注策略设计的关键因素，例如射流穿透深度和沿支板的孔板位置以及相对于腔的注入器位置。进行了一系列燃烧实验来评估喷射策略的火焰保持特性，从而将混合结果（以路径集成燃料密度表示）与燃烧器的稳定性能联系起来。虽然路径密度不太直观，但其在情况之间的比例性使定位在稳定包络内。此外，路径密度是与数值模拟成果直接比较的有用量。总之，这些发现突出了红外成像在研究混合趋势以指导超音速燃烧室先进液体燃料方案设计中的应用。

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引用次数: 0

Proper orthogonal decomposition of transient cavitating flow with emphasis on thermodynamic effect 适当的正交分解瞬态空化流，重点考虑热力学效应

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-16 DOI: 10.1016/j.expthermflusci.2025.111627

Bin Xu , Liwen Zhang , Desheng Zhang , Xi Shen , Weibin Zhang , B.P.M.Bart van Esch

This study employs data-driven modal decomposition methods to identify dominant coherent structures within fluoroketone cavitating flow around a NACA0015 hydrofoil, with particular emphasis on thermodynamic effects. Numerical simulations under isothermal and non-isothermal conditions provide snapshot data sequences within a thermosensitive cavitating flow modeling framework. Q-criterion vortex identification analyzes vortical structure evolution, while Proper Orthogonal Decomposition (POD) extracts dominant coherent structures and quantifies energy distribution characteristics. Power spectral density analysis identifies characteristic frequencies, and flow field reconstruction validates modal contributions. Results demonstrate that thermodynamic effects significantly suppress cavitation phenomena by reducing cavity volumes and prolonging evolution cycles through latent heat absorption-induced local temperature decreases and saturated vapor pressure reduction. The dominant shedding frequency exhibits strong correlation with vortex structure periodicity. POD analysis reveals that thermal effects preserve spatial topological characteristics of coherent structures while substantially attenuating dynamic intensities across all leading modes. Non-isothermal conditions require additional modes for equivalent reconstruction accuracy, indicating enhanced flow complexity due to temperature gradient-induced instabilities. The analysis demonstrates that thermodynamic effects fundamentally alter cavitating flow dynamics through systematic suppression of coherent structure intensities while preserving spatial organizational patterns. Enhanced energy dispersion across multiple modes under thermal influence necessitates modified modeling approaches for accurate flow prediction and control in thermosensitive cavitating systems.

本研究采用数据驱动的模态分解方法来识别NACA0015水翼周围氟酮空化流中的优势相干结构，并特别强调热力学效应。等温和非等温条件下的数值模拟提供了热敏空化流建模框架内的快照数据序列。q准则涡识别分析了涡旋结构演变，适当正交分解（POD）提取优势相干结构并量化能量分布特征。功率谱密度分析确定了特征频率，流场重建验证了模态贡献。结果表明，热力效应通过潜热吸收引起的局地温度降低和饱和蒸汽压降低显著抑制空化现象，减少空化体积，延长演化周期。主导脱落频率与涡结构周期性有很强的相关性。POD分析表明，热效应保留了相干结构的空间拓扑特征，同时大大减弱了所有主模态的动态强度。非等温条件需要额外的模式来获得等效的重建精度，这表明由于温度梯度引起的不稳定性增加了流动的复杂性。分析表明，热力学效应通过系统地抑制相干结构强度，同时保持空间组织模式，从根本上改变了空化流动动力学。在热敏空化系统中，热影响下多模态能量弥散增强，需要改进建模方法以实现精确的流动预测和控制。

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引用次数: 0

Heat penetration in reactive porous beds 反应性多孔床的热渗透

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-16 DOI: 10.1016/j.expthermflusci.2025.111631

André V. Xavier , Tarek L. Rashwan , Flávio L.F. Bittencourt , Marcio Ferreira Martins

This study investigates how the ignition method, diffusion-, and convection-driven influences heat penetration in a reactive porous bed of coconut-shell charcoal. A series of 28 controlled experiments was conducted under both diffusion- and convection-driven combustion modes, varying ignition protocols and thermocouple depths within a custom-designed combustion cell. The temperature evolution was measured to delineate heat penetration zones, including water condensation, preheating, and chemical reaction fronts. Results reveal that in assisted ignition, continuous external heating sustains combustion and deepens heat penetration by maintaining high-temperature gradients. In contrast, non-assisted ignition, which relies solely on internal heat release, exhibits faster cooling and limited penetration due to early heat loss and extinction risk. Heat maps constructed from the data show broader preheating zones under diffusion conditions and more pronounced condensation layers under convection. These findings highlight the critical role of ignition conditions in modulating thermal gradients and sustaining smoldering fronts, with implications for fire safety, waste-to-energy systems, and porous media combustion modeling.

本研究探讨了点火方式、扩散驱动和对流驱动如何影响椰壳炭反应多孔床的热渗透。在一个定制设计的燃烧电池中，在扩散和对流驱动的燃烧模式、不同的点火方案和热电偶深度下，进行了一系列28项对照实验。通过测量温度演变来描绘热渗透区，包括冷凝水、预热和化学反应前沿。结果表明，在辅助点火过程中，持续的外部加热通过维持高温梯度来维持燃烧并加深热渗透。相比之下，非辅助点火，完全依赖于内部热释放，表现出更快的冷却和有限的穿透，由于早期热损失和熄灭的风险。根据数据构建的热图显示，扩散条件下的预热区更宽，对流条件下的冷凝层更明显。这些发现强调了点火条件在调节热梯度和维持阴燃前沿方面的关键作用，对消防安全、废物转化为能源系统和多孔介质燃烧建模具有重要意义。

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引用次数: 0

A study of effect of physical properties on the impact of drop on a liquid pool for an immiscible reactive system 非混相反应体系中液滴对液池影响的物理性质研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-15 DOI: 10.1016/j.expthermflusci.2025.111628

Vishal Kumar, Sumana Ghosh, Shabina Khanam

Droplet impact on a liquid film or pool is a unique phenomenon that can be observed in different industrial applications and natural processes. The drop impact associated with chemical reaction with pool liquid is often utilized in the preparation of emulsions (single or double) for the encapsulation of various active reagents. The present study investigates the effects of viscosity on drop dynamics before and after impact on the liquid pool for an immiscible reactive system. The drop is made of various wt% of sodium alginate and calcium carbonate and the pool is comprised of soybean oil that contains acetic acid. In the present work, the impact process is studied for varying concentrations of sodium alginate and calcium carbonate drops at different impact heights. Two different situations are studied. In one case, the drop viscosity is lower than that of the pool and in the other two cases, the drop viscosities are much higher than that of the pool. It has been observed that maximum crater depth increases with impact height for the later cases. Also, the crater takes time to retract and thus, subsequent drop formation is delayed. However, the size of the drops is smaller and pinches-off quickly. The impact of a low viscous liquid on a high viscous pool produces a swallow crater that is closed quickly, while pinch-off is delayed in other cases. Different phenomena, such as jet and crater formation, crowning and drop fragmentation are captured using a high-speed camera. The images are processed using ImageJ software. Finally, a theoretical model based on energy conservation has been developed to predict the crater depth based on the physical properties of the liquids.

液滴对液膜或液池的影响是一种独特的现象，可以在不同的工业应用和自然过程中观察到。与池液化学反应相关的滴冲击常用于制备乳液（单或双），用于包封各种活性试剂。本文研究了非混相反应体系撞击液池前后粘度对液滴动力学的影响。滴液由不同wt%的海藻酸钠和碳酸钙组成，池由含有乙酸的大豆油组成。本文研究了不同浓度的海藻酸钠和碳酸钙滴剂在不同的冲击高度下的冲击过程。研究了两种不同的情况。在一种情况下，液滴粘度低于水池，在另外两种情况下，液滴粘度远高于水池。已观察到，在较晚的情况下，最大陨石坑深度随撞击高度的增加而增加。此外，陨石坑需要时间来收缩，因此，后续的液滴形成被推迟。然而，液滴的大小更小，而且很快就会脱落。低粘性液体对高粘性池的冲击会产生一个迅速闭合的吞坑，而在其他情况下，挤压会延迟。不同的现象，如喷射和陨石坑的形成，冠状和掉落碎片使用高速相机捕捉。图像处理使用ImageJ软件。最后，根据液体的物理性质，建立了基于能量守恒的理论模型来预测弹坑深度。

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引用次数: 0

Investigation into the bag breakup and sub-droplet size distribution of tandem water droplet pair in an elevated-temperatures continuous airflow 高温连续气流中串联水滴对破袋及亚滴粒径分布的研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-10-04 DOI: 10.1016/j.expthermflusci.2025.111625

Ke Zheng , Yufei Zhu , Zhiwen Gan

Understanding droplet interaction mechanisms in dense sprays requires investigation of tandem droplet pair fragmentation. This investigation uses a high-speed camera to examine the fragmentation phenomena and sub-droplet distribution of tandem water droplet pair with separation distances (S) ranging from 1.9 to 13.3 under airflow temperatures between 293 K and 493 K. The separation distance is the ratio of the actual spacing to the droplet diameter. Within a critical separation distance, the bag breakup of the lead droplet is influenced by collision with the trailing droplet. The critical separation distance for the lead droplet bag breakup decreases with airflow temperature. Separation distance and airflow temperature influence the trailing droplet bag breakup through the collision with the lead droplet, the lead droplet shielding effect, and the airflow velocity dissipation. Further, the sub-droplet size distribution of the broken lead droplet is analyzed by dividing the broken droplet into three parts: bag, rim, and node. The correlation length governing the bag sub-droplet size primarily depends on the bag thickness, while the rim and node sub-droplet sizes depend on the liquid ring thickness. Separation distance and airflow temperature affect the sub-droplet size distributions by altering the volume fractions of the bag, rim, and node, as well as their correlation lengths. A semi-empirical model for predicting the Sauter mean diameter (SMD) of the sub-droplet of the broken lead droplet is proposed based on the volume fractions of different parts (bag, rim, and node) and their correlation lengths. The predictions align well with the experimental data among across a wide range in this investigation. This investigation can provide experimental data and theoretical references for understanding the droplet interaction mechanisms within dense sprays.

了解密集喷雾中液滴的相互作用机制需要对串联液滴对破碎进行研究。利用高速摄像机研究了在293 ~ 493 K气流温度下，分离距离(S)为1.9 ~ 13.3的串联水滴对的破碎现象和亚滴分布。分离距离是实际间距与液滴直径之比。在一定的临界分离距离内，铅滴破袋受尾滴碰撞的影响。铅滴破袋的临界分离距离随气流温度的升高而减小。分离距离和气流温度通过与铅滴的碰撞、铅滴的屏蔽作用和气流速度耗散影响尾滴袋破碎。进一步，通过将破铅液滴分为袋、边缘和节点三部分，分析破铅液滴的子液滴尺寸分布。控制袋状子液滴大小的相关长度主要取决于袋状厚度，而边缘和节点子液滴大小则取决于液环厚度。分离距离和气流温度通过改变袋状、边缘状和结状的体积分数及其相关长度来影响子液滴粒径分布。提出了一种基于不同部位（包、边缘和节点）的体积分数及其相关长度预测破铅液滴子液滴Sauter平均直径（SMD）的半经验模型。这些预测与本研究中广泛范围内的实验数据吻合得很好。该研究可为深入了解致密雾剂中液滴相互作用机理提供实验数据和理论参考。

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引用次数: 0

Experimental study on cavitation pattern and near-field spray characteristics of methanol in the scaled-up fuel injection nozzle 甲醇在放大喷油器内的空化模式及近场喷射特性实验研究

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-26 DOI: 10.1016/j.expthermflusci.2025.111624

Wei Huang , Yizhou Yang , Zhixia He , Zhen Yang , Shengnan Zhang , Yuanfeng Zhao , Wei Guan , Genmiao Guo

Methanol, as a clean fuel, particularly when synthesized from green electricity and recycled CO₂, has zero-carbon potential and is gaining increasing attention. However, due to methanol’s corrosivity and unique physical properties, designing high-pressure injectors for methanol engines presents numerous challenges. This study presents the first comprehensive analysis of methanol’s flow characteristics and near-field spray behavior using a scaled-up optical nozzle. Rounded and sharp nozzles were used to investigate vortex-induced string cavitation and geometry-induced sheet cavitation. By adjusting the needle lift and injection pressure, the onset and development of various cavitation patterns in methanol were studied. Additionally, comparative experiments between methanol and diesel were conducted to analyze the differences in flow and spray characteristics under different cavitation regimes, providing insights for the use of methanol as a replacement for diesel in engines. Experimental results show that methanol’s lower viscosity promotes the exsolution of dissolved gases, forming free gas bubbles that accumulate in the vortex core, thereby enhancing string cavitation. Under identical operating conditions, methanol exhibits a stronger tendency for string cavitation and greater cavitation intensity compared to diesel. In contrast, the difference in geometric-induced cavitation intensity between methanol and diesel is relatively small, attributed to methanol’s less sensitive response to variations in fuel properties.

甲醇作为一种清洁燃料，特别是由绿色电力和回收二氧化碳合成的甲醇，具有零碳潜力，越来越受到关注。然而，由于甲醇的腐蚀性和独特的物理性质，为甲醇发动机设计高压喷油器带来了许多挑战。本研究首次采用放大光学喷嘴对甲醇的流动特性和近场喷雾行为进行了全面分析。采用圆形和尖形喷嘴分别研究了涡致柱状空化和几何致片状空化。通过调整注射针升程和注射压力，研究了甲醇中各种空化模式的发生和发展。此外，还进行了甲醇和柴油的对比实验，分析了不同空化制度下甲醇的流动和喷雾特性的差异，为在发动机中使用甲醇替代柴油提供了见解。实验结果表明，甲醇较低的粘度促进了溶解气体的析出，形成自由气泡积聚在涡核中，从而增强了串的空化作用。在相同工况下，甲醇比柴油表现出更强的空化倾向和更大的空化强度。相比之下，甲醇和柴油在几何诱导空化强度上的差异相对较小，这是由于甲醇对燃料特性变化的响应不太敏感。

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引用次数: 0

Thermally induced nanobubble filaments and cylindrical shock wave formation in colloidal suspension 胶体悬浮液中热诱导纳米气泡细丝和圆柱激波的形成

IF 3.3 2区工程技术 Q2 ENGINEERING, MECHANICAL

Experimental Thermal and Fluid Science

Pub Date : 2025-09-24 DOI: 10.1016/j.expthermflusci.2025.111623

Uroš Orthaber, Rok Petkovšek

An interesting phenomenon involving generation of nanobubble filaments in an aqueous colloidal suspension of gold nanoparticles (GNP) is being reported on and discussed in the present paper. The heat for thermally induced nanobubbles is being provided to GNPs by a laser pulse. If specific conditions, such as sufficient laser beam fluence, adequate GNP size and concentration are met self-focusing occurs, which consequently leads to a formation of one or more nanobubble filaments along the beam propagation direction. The nanobubble filaments are made observable by sending a rarefaction wave through the region, where they occur. Depending on the beam fluence, one or more nanobubble filaments are observed and depending on the beam and GNP parameters, the nanobubble filaments may be accompanied by a plasma filament, if thresholds for self-focusing and ionization are exceeded at the same time. In this case a cylindrical shock wave originating from the filament is observed. The present study investigates the influence of GNP size and beam fluence on nanobubble filament formation. It implements a recently developed technique for nanobubble visualization using a rarefaction wave and a multiple illumination pulse technique for shock wave detection.

本文报道并讨论了在金纳米颗粒（GNP）的胶体悬浮液中产生纳米气泡细丝的有趣现象。热诱导纳米气泡的热量由激光脉冲提供给GNPs。如果满足特定条件，如足够的激光束通量、足够的GNP大小和浓度，就会发生自聚焦，从而导致沿光束传播方向形成一个或多个纳米气泡细丝。纳米气泡细丝是通过发送稀薄波穿过它们出现的区域而被观察到的。根据光束的影响，可以观察到一个或多个纳米气泡细丝，根据光束和GNP参数，如果同时超过自聚焦和电离的阈值，纳米气泡细丝可能伴随着等离子体细丝。在这种情况下，观察到从灯丝发出的圆柱形激波。本文研究了GNP尺寸和光束影响对纳米泡丝形成的影响。它实现了最近开发的纳米气泡可视化技术，使用稀疏波和多重照明脉冲技术进行冲击波检测。

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引用次数: 0

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