Experiments in Fluids最新文献

{"title":"Discrete motion modes of eccentric droplet impact on sessile droplet at low Ohnesorge and Weber numbers","authors":"Mengqi Yan,&nbsp;Zhenyu Ouyang,&nbsp;Chen Liu,&nbsp;Chengxu Tu,&nbsp;Fubing Bao,&nbsp;Jianzhong Lin","doi":"10.1007/s00348-025-04060-7","DOIUrl":"10.1007/s00348-025-04060-7","url":null,"abstract":"<div><p>This paper presents an experimental study on the discrete motion characteristics of droplets colliding with sessile droplets at low Weber and Ohnesorge numbers. Droplets generated by a micro-injection pump impact sessile droplets on a stainless-steel flat plate, with the process recorded by a high-speed camera and data collected using a micro-force sensor. The results show three distinct modes of droplet behavior upon collision with the sessile droplet: rebound and coalescence, rebound and separation, and slide and coalescence. Apart from these modes, direct coalescence is the dominant outcome under most experimental conditions, while this study specifically focuses on the less frequent discrete behaviors to explore the dynamics of such motions. As the eccentric distance between the impacting droplet and the sessile droplet increases, these three discrete modes transition sequentially. Changes in the volume ratio between the sessile droplet and the impacting droplet shift the boundaries of these modes along the eccentric distance. The effect of eccentric distance on contact-line spacing transitions from promoting to suppressing. An increase in the volume ratio leads to greater kinetic energy dissipation of the impacting droplet and reduces its rebound height. During the coalescence and rebound events, two pressure peaks are observed on the wall surface, but the origins and temporal intervals of these peaks differ. The volume ratio significantly affects the peak impact pressure and contact time. This study contributes to a deeper understanding of the process of continuous droplet impact on wall surfaces.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 7","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145165273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The spectral response of time-resolved PIV in a turbulent boundary layer","authors":"Peter Manovski,&nbsp;Wagih Abu Rowin,&nbsp;Henry Ng,&nbsp;Paul Gulotta,&nbsp;Matteo Giacobello,&nbsp;Charitha de Silva,&nbsp;Nicholas Hutchins,&nbsp;Ivan Marusic","doi":"10.1007/s00348-025-04059-0","DOIUrl":"10.1007/s00348-025-04059-0","url":null,"abstract":"<div><p>This study presents the application of time-resolved particle image velocimetry (TR-PIV) to measure the mean and fluctuating velocity components in a turbulent boundary layer (TBL) over an axisymmetric body of revolution. A narrow wall-normal strip of the flow was captured using a synchronised high-speed laser and camera at a recording frequency of up to 80 kHz. The resulting streamwise and wall-normal velocity TR-PIV data were validated against hot-wire anemometry measurements and direct numerical simulations (DNS) of a flat plate under matched flow conditions. The mean flow results showed good agreement between all methods, while the expected attenuation due to the spatial averaging was found in the TR-PIV turbulence statistics closer to the wall. A key outcome of this study is the establishment of an effective laser sheet thickness for the TR-PIV using DNS as a reference. This study fills a gap in understanding the spectral response and limitations of TR-PIV in such complex flows, particularly how spatial resolution and noise influence the accuracy of turbulence measurements. The TR-PIV streamwise velocity energy spectra were compared with DNS data that were spatially filtered to match the resolution of the TR-PIV and hot-wire. A transfer function was derived to determine cut-off wavelengths as a function of wall-normal distance. The cut-off wavelengths enabled the quantification of the resolvable turbulence scales within the TBL, revealing that the spatial resolution is a limiting factor for TR-PIV. The methodology was applied to locations with zero and favourable pressure gradients, providing insights into how pressure gradients influence spectral content and the limitations of TR-PIV in capturing the full range of turbulence scales. The outlined methodology is applicable more broadly and can be used to enhance the accuracy of experimental techniques in future boundary layer investigations.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 7","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04059-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effects of the formation of shear-driven liquid-surface waves on the gas-phase turbulent boundary layer","authors":"Nikolay Gustenyov,&nbsp;Sean C. C. Bailey","doi":"10.1007/s00348-025-04054-5","DOIUrl":"10.1007/s00348-025-04054-5","url":null,"abstract":"<div><p>The gas-phase boundary layer evolution following transition from smooth-solid-wall to liquid-surface boundary conditions is characterized and contrasted with the evolution of a turbulent boundary layer over a smooth, solid wall of equivalent length. It was observed that an internal boundary layer forms following the development of stochastic surface waves. The internal boundary layer exhibits displaced momentum away from the surface and increased turbulence intensity compared to smooth-wall boundary layers. Scaling analyses indicate that mean velocity scaling resembles that of rough-walled turbulent boundary layers when scaled with a friction velocity value that was the same as the friction velocity immediately upstream of the liquid surface. Within the internal boundary layer, the streamwise Reynolds stress deviates markedly from the solid-wall behavior. Spectral analysis reveals that turbulence near the liquid surface is generated at wavenumbers corresponding to the surface waves, accompanied by additional small-scale turbulence. These differences are localized near the surface, with spectral characteristics converging toward those of a solid-wall boundary layer as the measurement point moves further from the surface. The turbulent kinetic energy dissipation rate differs significantly between liquid and solid surfaces, reflecting changes to the small-scale structure. A surrogate friction velocity capable of scaling the Kolmogorov length scale near the surface also demonstrates success in scaling the turbulence within the internal boundary layer, revealing that the streamwise Reynolds stress adheres to a logarithmic scaling similar to that observed in the overlap region of high Reynolds number wall-bounded flows.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 7","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164587","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Transition phenomena and intermittency on a Mach 6 flat plate evaluated by three independent flow parameters","authors":"Jens Lunte,&nbsp;Erich Schülein","doi":"10.1007/s00348-025-04034-9","DOIUrl":"10.1007/s00348-025-04034-9","url":null,"abstract":"<div><p>Heat transfer rates, wall pressure and density fluctuations of a flat-plate boundary layer within the laminar–turbulent transition zone were measured at Mach 6 freestream conditions. The combination of the three independent flow parameters enables an extensive insight into the transition phenomena, improves the interpretation of the data and identifies the limitations of the respective measurement techniques. Comparisons between the measurement data culminate in the quantitative description of the transition progress by means of the intermittency distributions, which were calculated from each flow parameter individually. The derived transition locations differ by up to 9.3% in streamwise direction in relation to the average transition Reynolds number.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 7","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04034-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164589","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Quantitative characterization of elongated bubble breakup dynamics in intermittent flow using Stereo-PIV/PLIF","authors":"Haixia Wang,&nbsp;Ting Xue","doi":"10.1007/s00348-025-04045-6","DOIUrl":"10.1007/s00348-025-04045-6","url":null,"abstract":"<div><p>The deformation and detachment of elongated bubbles substantially impact the heat and mass transfer efficiency in intermittent flow. To investigate the criterion of elongated bubble breakup induced by flow conditions, a high-speed optical system integrating monocular stereo particle image velocimetry (Stereo-PIV) and planar laser-induced fluorescence (PLIF) is proposed to monitor synchronously the interfacial structures and three-dimensional flow parameters of intermittent flow. High-speed photography is utilized to judge the presence of small bubbles and determine the critical flow conditions leading to elongated bubble breakup. Meanwhile, the PLIF technique is applied to capture the interfacial structure of elongated bubbles and analyze their temporal variations with flow conditions, while monocular Stereo-PIV is employed to obtain the liquid velocity field. However, the diversity of the full-component velocities with flow conditions makes it difficult to directly reveal the criterion for the transition of elongated bubbles from an intact state to a broken state. To address this limitation, vorticity and vorticity stretching terms are employed to analyze elongated bubble deformation, revealing a strong correlation between the variation of elongated bubble length and vorticity as well as vortex stretching. Furthermore, statistical analyses of turbulent kinetic energy and Weber number are performed, revealing that the critical turbulent kinetic energy for bubble breakup is 0.02 m²/s², and the critical Weber number is 4, consistent with the findings of F. Lehr. Turbulent normal stress, turbulent shear stress, and their combinations are identified as potential destructive forces for elongated bubble breakup, primarily induced by turbulent fluctuations and interfacial instability. These findings provide new insights and data support for theoretical research and engineering application of elongated bubble breakup in horizontal intermittent flow.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of throat diameter on the cavitation phenomenon inside an aerated Venturi tube for microbubble production","authors":"Noor Saffreena Hamdan,&nbsp;Akiko Kaneko","doi":"10.1007/s00348-025-04032-x","DOIUrl":"10.1007/s00348-025-04032-x","url":null,"abstract":"<div><p>Aeration in Venturi tubes for microbubbles production has become popular in recent years as it enhanced the transportation of oxygen and other gases in wastewater treatment and mineral engineering. In an aerated Venturi, air/gas was injected upstream into the flowing liquid inside the Venturi tube. The air flows inside the Venturi tube as bubbles, before breakup occurs downstream after the throat area. This method promoted the transportation of particular gases or substances in microbubbles. To further increase the generation of microbubbles, flowing liquid velocity was increased by decreasing the throat diameter, but cavitation started to emerge inside the tube as velocity increased. This present study aims to investigate the effect of reducing the throat diameter on the cavitation number of the aerated Venturi tube and how it affects the breakup characteristics of bubbles. Activities involved in the investigation were: visualization of flow and generated microbubbles, image processing of the images captured, pressure and void fraction measurement, and calculating the cavitation number. The result showed that reducing the throat diameter initiated the cavitation occurrence earlier, and in aerated cases, cavitation exists in the form of cavitated bubbles. Aeration also affects the cavitation number in a non-cavitated flow but does not significantly affect the existing cavitated flow. Reducing the throat diameter also successfully increased the generation of bubbles less than 0.2 mm, but the overall SMD did not show a straightforward relationship with cavitation number.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04032-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164547","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Neural optical flow for planar and stereo PIV","authors":"Andrew I. Masker,&nbsp;Ke Zhou,&nbsp;Joseph P. Molnar,&nbsp;Samuel J. Grauer","doi":"10.1007/s00348-025-04058-1","DOIUrl":"10.1007/s00348-025-04058-1","url":null,"abstract":"<div><p>Neural optical flow (NOF) offers improved accuracy and robustness over existing OF methods for particle image velocimetry (PIV). Unlike other OF techniques, which rely on discrete displacement fields, NOF parameterizes the physical velocity field using a continuous neural-implicit representation. This formulation enables efficient data assimilation and ensures consistent regularization across views for stereo PIV. The neural-implicit architecture provides significant data compression and supports a space–time formulation, facilitating the analysis of both steady and unsteady flows. NOF incorporates a differentiable, nonlinear image-warping operator that relates particle motion to intensity changes between frames. Discrepancies between the advected intensity field and observed images form the data loss, while soft constraints, such as integrated Navier–Stokes residuals, enhance accuracy and enable direct pressure inference from PIV images. Additionally, mass continuity can be imposed as a hard constraint for both 2D and 3D flows. Results from synthetic planar and stereo PIV datasets, as well as experimental planar data, demonstrate that NOF outperforms state-of-the-art wavelet-based OF, cross-correlation, and selected supervised machine learning methods. Beyond PIV, NOF could be used in conjunction with techniques like background-oriented schlieren, molecular tagging velocimetry, and other advanced measurement systems. </p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04058-1.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164548","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hypersonic boundary-layer transition on the BOLT forebody in the R2Ch facility","authors":"Loïc Sombaert,&nbsp;François Nicolas,&nbsp;Mathieu Lugrin,&nbsp;Nicolas Severac,&nbsp;Sebastien Esquieu,&nbsp;Reynald Bur","doi":"10.1007/s00348-025-04046-5","DOIUrl":"10.1007/s00348-025-04046-5","url":null,"abstract":"<div><p>Laminar-to-turbulent boundary-layer transition is investigated on a 1:3-subscale BOLT model within the ONERA R2Ch hypersonic wind tunnel. The study is conducted at Mach numbers of 6 and 7 over a wide range of Reynolds numbers, enabling observations of the entire transition process over a large portion of the geometry. Infrared thermography measurements are used to track the evolution of transition onset. High-frequency wall pressure transducers (PCB) provide insights into transitional instabilities on the central and outboard regions. Pressure spectra analysis reveals amplified spectral energy content, associated with different instabilities, when the Reynolds number is increased. At Mach 7, a high-frequency instability (<span>(fapprox 140)</span>–250 kHz), believed to be a second Mack mode, is found to be amplified on the outboard region. However, given its absence from Mach 6 results which display very similar transition fronts and the small spatial amplification, the role it plays in the transition process remains unclear. A different instability mechanism is found in the central region, with a lower-frequency range. The computation of the instabilities’ streamwise propagation velocities also highlights significant disparities between the central and outboard regions. Comparing these values with laminar CFD results provides further insights into characterizing these instabilities. Additionally, the study investigates signal intermittency by examining the high-frequency content of spectrograms to point out the emergence of turbulent spots.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145163635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Splashing of viscous droplets on heated surfaces","authors":"Shiji Lin,&nbsp;Le Zhou,&nbsp;Longquan Chen,&nbsp;Zhigang Li","doi":"10.1007/s00348-025-04057-2","DOIUrl":"10.1007/s00348-025-04057-2","url":null,"abstract":"<div><p>The splashing dynamics of low-viscosity droplets impinging on heated surfaces has been extensively studied. For high-viscosity droplets, however, the roles of viscosity and surface temperature in droplet splash are unknown. In this work, we investigate droplet splashing on heated surfaces through experiments and theoretical analyses. Specifically, the critical Weber numbers (<span>(We)</span>), <span>(W{e}_{C})</span>, for droplet splash are obtained through experiments for a wide range of surface temperatures, <span>({T}_{S})</span>, and Ohnesorge numbers. It is found that the thermal stabilization effect, i.e., droplet splash is suppressed by a heated surface, for low-viscosity droplets also holds for droplets with high viscosity. However, the thermal stabilization effect becomes less sensitive to surface temperature for high-viscosity droplets. Furthermore, the dual roles of viscosity in droplet splash, i.e., low-viscosity droplets promote splash, while high-viscosity droplets impede splash when viscosity increases, are found to be independent of surface temperature. Theoretical analysis reveals that thermal stabilization arises from gas-phase aerodynamics and lubrication effects, while the dual roles of viscosity are due to the competition between capillary stabilization and viscous damping. The findings in this work provide useful information for controlling droplet splashing in various applications, such as thermal spray coating and additive manufacturing.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145163636","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental investigation of effects of spanwise segmented blowing on a circulation control wing with a dual-radius flap","authors":"Tulasi Ram Vechalapu,&nbsp;Konstantinos Kanistras,&nbsp;Chang-Kwon Kang","doi":"10.1007/s00348-025-04055-4","DOIUrl":"10.1007/s00348-025-04055-4","url":null,"abstract":"<div><p>The aim of this study is to explore the efficacy of spanwise segment blowing in an attempt to reduce the mass flow requirements while improving aerodynamic efficiency. For this study a modified NACA0012 wing with three plena is chosen. Direct force and 2D PIV measurements are collected at three spanwise locations to examine the impact of segmented on demand blowing. Further stereoscopic PIV measurements are conducted to investigate the aerodynamic effects of individual blowing, dual blowing, and uniform blowing configurations on wake dynamics. The results of the force measurements combined with the 2D PIV measurements demonstrate that only one-third of the mass flow is required when employing segmented blowing while maintaining the same lift and rolling moments coefficients. Stereo-PIV measurements reveal that initially the tip vortex is stronger, but increased blowing intensifies the root vortex, eventually surpassing the tip vortex. The results also showed that only the adjacent plenum has an effect on the root vortex, whereas the tip vortex is influenced by blowing from all three plenums, underscoring its sensitivity to interactions across multiple locations. </p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 6","pages":""},"PeriodicalIF":2.5,"publicationDate":"2025-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145164082","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}