Experiments in Fluids最新文献

Evaluation of an event-based camera for time-resolved imaging of primary atomization in an air-assist atomizer

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-04-03 DOI: 10.1007/s00348-025-04009-w

Kuppuraj Rajamanickam, Yannis Hardalupas

{"title":"Evaluation of an event-based camera for time-resolved imaging of primary atomization in an air-assist atomizer","authors":"Kuppuraj Rajamanickam, Yannis Hardalupas","doi":"10.1007/s00348-025-04009-w","DOIUrl":"10.1007/s00348-025-04009-w","url":null,"abstract":"<div><p>The current work discusses the demonstration of an event-based (EB) camera for time-resolved imaging (10,000 frames/sec) of the primary atomization of a canonical air-assist atomizer. Experiments were performed simultaneously with conventional high-speed and event-based cameras, enabling us to quantitatively assess the performance of event-based cameras in spray imaging (particularly near-field liquid jet breakup) applications. Three atomization breakup regimes are considered: columnar, bag, and multimode. Dynamic mode decomposition (DMD) was implemented to analyze the acquired instantaneous time-dependent images from both cameras and assess their performance in extracting turbulence statistics of the primary atomization. The computed DMD frequency spectrum and spatial modes of liquid breakup characteristics from the images recorded from both cameras are comparable, highlighting the potential of event-based cameras in extracting coherent structures in the primary atomization zone and their spectral contents. However, in some instances, the EB camera underpredicts the DMD modes compared to high-speed cameras, and the reasons for these discrepancies were explained. Finally, the limitations (e.g., event saturation) of event-based cameras in the context of primary atomization imaging were also discussed.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04009-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143769679","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}

引用次数: 0

Elliptic synthetic jet vortex rings impinging onto a solid wall: effect of Reynolds number

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-04-03 DOI: 10.1007/s00348-025-04004-1

Guoan Wen, Lei Wang, Yang Xu

{"title":"Elliptic synthetic jet vortex rings impinging onto a solid wall: effect of Reynolds number","authors":"Guoan Wen, Lei Wang, Yang Xu","doi":"10.1007/s00348-025-04004-1","DOIUrl":"10.1007/s00348-025-04004-1","url":null,"abstract":"<div><p>Time-resolved stereoscopic particle image velocimetry is employed to analyze the behavior of elliptic synthetic jet vortex rings impinging onto a solid wall. Reconstruction of three-dimensional flow field is achieved using a phase-locked method. Three jet Reynolds numbers (<i>Re</i><sub><i>sj</i></sub> = 318, 477, and 636) are investigated while maintaining a constant orifice-to-wall distance (<i>H</i><sub>0</sub>/<i>D</i><sub>0</sub> = 5) and orifice aspect ratio (<i>AR</i> = 3). The results show that the elliptic vortex ring with non-uniform distribution of the circulation induces asymmetric secondary vortex, which is different from circular ring-wall interaction. The process of impingement is divided into three stages: strong interaction, weak interaction, and stable expansion. During the stable expansion stage, the elliptic vortex ring exhibits two scenarios: into a circle and into an ellipse. The difference can be explained as follows: in the strong interaction stage, the expansion of the primary vortex ring after the impingement is mainly influenced by both the self-induction of the noncircular vortex ring and the vortex strength. However, in the weak interaction stage, it is primarily affected by the latter effect owing to the reduced three-dimensionality of the vortex ring. Under different Reynolds numbers, the vortex rings undergo different phases of the axis switching process before the vortex-wall interaction, resulting in their different final shapes. In addition, the time-averaged flow characteristics are investigated by considering azimuthally averaged velocity fields. With increasing Reynolds number, the maximum radial velocity, turbulent kinetic energy, radial mass flow rate, and momentum flux increase. In particular, the maximum radial velocity distribution can match well with the final shapes of the vortex rings.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143769812","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}

引用次数: 0

An experimental investigation on the effect of laser energy deposition in an over-expanded jet 关于过度膨胀喷流中激光能量沉积效应的实验研究

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-04-02 DOI: 10.1007/s00348-025-04008-x

S. Syam, Gauresh Raj Jassal, Bryan E. Schmidt

{"title":"An experimental investigation on the effect of laser energy deposition in an over-expanded jet","authors":"S. Syam, Gauresh Raj Jassal, Bryan E. Schmidt","doi":"10.1007/s00348-025-04008-x","DOIUrl":"10.1007/s00348-025-04008-x","url":null,"abstract":"<div><p>This experimental investigation focuses on understanding the influence of perturbations due to short-duration energy deposition on the shock train structure and flow dynamics in an axisymmetric over-expanded Mach 2.52 jet. The flow is perturbed by localized laser-induced breakdown at various locations within the jet, creating a shock wave and a high-temperature plasma zone in the shock train. A high-speed self-aligning focusing schlieren system is used to visualize the flow and characterize the shock train dynamics and the flow structure recovery process by measuring the distance to the first shock reflection point from the nozzle exit. The response of the jet flow is similar for cases with the perturbation at the nozzle exit and the pre-reflection point across a range of jet total pressures, but the response is qualitatively different when the perturbation occurs downstream of the first shock reflection in the jet, with the flow structures being forced upstream toward the nozzle. The frequency of the oscillations of the shock height is found to be the same for all cases, approximately 10 kHz, independent of the jet total pressure, laser energy, and deposition location. The oscillations reduce in magnitude over time, and the damping ratio for cases with the energy deposition at the pre-reflection point and nozzle exit is found to be nearly constant with respect to jet total pressure and deposition energy, varying within the range of 0.06–0.12, whereas it is dependent on the jet chamber pressure for the post-reflection case, varying from 0.07 to 0.14.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04008-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143761682","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}

引用次数: 0

Three-dimensional tracking of microswimmer suspensions

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-28 DOI: 10.1007/s00348-025-04002-3

Junaid Mehmood, Koen Muller, Sowmya Kumar, Abel-John Buchner, Daniel Tam

{"title":"Three-dimensional tracking of microswimmer suspensions","authors":"Junaid Mehmood, Koen Muller, Sowmya Kumar, Abel-John Buchner, Daniel Tam","doi":"10.1007/s00348-025-04002-3","DOIUrl":"10.1007/s00348-025-04002-3","url":null,"abstract":"<div><p>Understanding the locomotion of microorganisms is essential for insights into microbial ecology, infection, and colonization processes. Although two-dimensional microscopy has been widely used to study microswimmer motility, it does not capture the full extent of their three-dimensional (3D) movement. Recent advances in defocused particle tracking, holographic tracking velocimetry, and stereo-microscopy face challenges in achieving high resolution at larger particle densities and tracking multiple microswimmers in suspension. In this work, we introduce a novel multi-camera microscopy system that significantly improves the accuracy of 3D microswimmer tracking. Our system uses four sCMOS cameras to image microorganisms within a 2.5 <span>(times)</span> 2.5 <span>(times)</span> 2 mm<span>(^3)</span>. We assess the performance of our microscopy system by tracking a population of the unicellular motile algae <i>Chlamydomonas reinhardtii</i>. An in-house tracking algorithm based on the projective geometry framework enables tracking with reprojection errors below 0.3 body lengths. This system supports imaging and tracking particle source densities of 0.32, higher than other existing single camera 3D microscopy techniques. Analysis of <i>C. reinhardtii</i> trajectories in 3D reveals a predominance of left-handed chirality and helical swimming patterns. Moreover, our 3D tracking data provide translational and rotational diffusion coefficients that differ from those obtained using traditional two-dimensional methods.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04002-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143726700","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}

引用次数: 0

Non-intrusive estimation of the buffet loads on a supercritical airfoil with SCBs

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-26 DOI: 10.1007/s00348-025-04000-5

A. D’Aguanno, A. Corduas, F. F. J. Schrijer, B. W. van Oudheusden

{"title":"Non-intrusive estimation of the buffet loads on a supercritical airfoil with SCBs","authors":"A. D’Aguanno, A. Corduas, F. F. J. Schrijer, B. W. van Oudheusden","doi":"10.1007/s00348-025-04000-5","DOIUrl":"10.1007/s00348-025-04000-5","url":null,"abstract":"<div><p>This study experimentally investigates the effect of three-dimensional shock control bumps (SCBs) on the aerodynamic loads of a supercritical airfoil under transonic buffet conditions. The experiments consisted in planar particle image velocimetry (PIV) measurements and have been carried out in the transonic-supersonic wind tunnel of TU Delft under fully developed buffet conditions (<span>(text {Ma}=0.7)</span> and <span>(alpha =3.5^{circ })</span>). The bumps are wedge-shaped and have been placed in the center of the shockwave oscillation range. Shock detection and phase-averaged velocity fields confirm that properly designed and spaced (<span>(Delta y_text {SCB}/c = 25%)</span>) SCBs reduce the shockwave oscillation range (compared to the clean case). The velocity data have been further used to evaluate the pressure field around the entire airfoil, and afterward, lift and drag coefficients have been retrieved, respectively, from momentum contour and wake integral approaches. Results demonstrate that SCBs have a beneficial effect on the aerodynamic loads with an increase in lift and a decrease in drag under fully developed buffet conditions. More importantly, a strong reduction of the amplitude of oscillations of both lift and drag coefficient, within the different buffet phases, was noted. Tests at multiple spanwise locations revealed relevant differences, with lower drag and higher lift values being achieved in the symmetry plane of a SCB, while a worse performance (with values comparable to the clean case) was achieved in the symmetry plane in between two adjacent bumps.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04000-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143706932","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}

引用次数: 0

High-speed fs/ps-CARS thermometry for supersonic H2/air combustion studies

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-25 DOI: 10.1007/s00348-025-04007-y

Clément Pivard, Michael Scherman, Rosa Santagata, Guillaume Pilla, Guillaume Pelletier, Thomas Le Pichon

{"title":"High-speed fs/ps-CARS thermometry for supersonic H2/air combustion studies","authors":"Clément Pivard, Michael Scherman, Rosa Santagata, Guillaume Pilla, Guillaume Pelletier, Thomas Le Pichon","doi":"10.1007/s00348-025-04007-y","DOIUrl":"10.1007/s00348-025-04007-y","url":null,"abstract":"<div><p>We present the results of a hybrid femtosecond/picosecond coherent anti-Stokes Raman scattering (fs/ps-CARS) thermometry campaign performed in a H<sub>2</sub>/air research supersonic scramjet combustor. In situ vertical and horizontal temperature profiles were retrieved upstream and downstream the combustion zone. The repetition rate of the measurement was adjusted in order to optimize the signal-to-noise ratio of the CARS signal depending on the local turbulence of the flow. Near the flame front, single-shot measurements were demonstrated at kHz rate to catch the high-speed temperature fluctuations. In steady flow zones downstream of the combustion, up to 100 shots integration was performed in order to increase the precision of the measurement. This measurement campaign allowed to build a valuable experimental database for comparison with a 3D numerical unsteady computational fluid dynamic (CFD) simulation developed at ONERA. This work demonstrates the efficiency of hybrid fs/ps-CARS to perform single-shot kHz thermometry inside large-scale supersonic combustor.</p><h3>Graphical abstract</h3><div><figure><div><div><picture><source><img></source></picture></div></div></figure></div></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143688493","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}

引用次数: 0

Density measurements via background-oriented schlieren and parallel-ray omnidirectional integration

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-22 DOI: 10.1007/s00348-025-04012-1

Jonathan Davami, Thomas J. Juliano, Jose R. Moreto, Xiaofeng Liu

{"title":"Density measurements via background-oriented schlieren and parallel-ray omnidirectional integration","authors":"Jonathan Davami, Thomas J. Juliano, Jose R. Moreto, Xiaofeng Liu","doi":"10.1007/s00348-025-04012-1","DOIUrl":"10.1007/s00348-025-04012-1","url":null,"abstract":"<div><p>Most measurements of density via background-oriented schlieren (BOS) numerically integrate the Poisson equation to calculate the density field from density gradients, which is susceptible to errors in measurements and uncertainties in boundary values. An alternative method, parallel-ray omnidirectional integration (ODI), was implemented and found to be significantly more accurate and precise. To compare the performance of the integration algorithms, a BOS displacement field was synthesized for the Taylor–Maccoll solution for inviscid, supersonic, conical flow. The impact of measurement error was simulated by adding noise to the synthetic displacement field. Density was reconstructed from 200 statistically independent displacement fields for two noise levels. The ODI algorithm resulted in higher accuracy and precision for all cases analyzed. In fact, the mean error for ODI at the highest noise level was found to be lower than that of Poisson integration, even when Poisson is evaluated without any input noise. These algorithms were also used to reconstruct density from experimental BOS measurements on a cone-flare model in hypersonic flow and zero angle of attack. This geometry exhibits a shock-wave/boundary-layer interaction which consists of bow, separation, and reattachment shocks and a recirculation bubble. The reconstructed density agreed excellently with the inviscid solution outside the boundary layer and recirculation bubble. The ODI-derived density field provided a closer match to the anticipated result than the Poisson-derived density, and is thus the recommended method. This work emphasizes the exceptional capability of ODI in reconstructing accurate and precise density fields from BOS measurements, thereby advancing the high spatial resolution, non-intrusive, and quantitative measurement technique used to deepen the understanding of complex fluid flows.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143676444","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}

引用次数: 0

Scanning laser-induced fluorescence for three-dimensional mixing characteristics of inclined dense jets with and without swirl

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-20 DOI: 10.1007/s00348-025-04005-0

Baoxin Jiang, Adrian Wing-Keung Law

{"title":"Scanning laser-induced fluorescence for three-dimensional mixing characteristics of inclined dense jets with and without swirl","authors":"Baoxin Jiang, Adrian Wing-Keung Law","doi":"10.1007/s00348-025-04005-0","DOIUrl":"10.1007/s00348-025-04005-0","url":null,"abstract":"<div><p>In this study, we introduce a novel laser imaging technique, named as scanning laser-induced fluorescence (SLIF), designed to quantify the time-averaged three-dimensional mixing behavior of inclined dense jets with and without swirl. SLIF builds upon the established planar laser-induced fluorescence (LIF) method, which is widely used for experimental studies on buoyant jets in the laboratory. Unlike traditional LIF which is typically stationary, SLIF involves towing a light sheet obliquely in a back-and-forth manner through the flow domain to generate a volumetric scan. Simultaneously, an imaging camera is also towed at an oblique angle to capture the LIF images synchronously, allowing for comprehensive three-dimensional concentration measurements within the scanned volume. Compared to previous scanning approaches, SLIF is able to provide spatial measurements without the concern of defocusing due to the fixed relative distance between the laser sheet and camera. For validations, laboratory experiments with turbulent non-buoyant jets were first conducted. The results demonstrated good agreement with existing literature data. Subsequently, SLIF was applied to quantify the mixing characteristics of 45-degree inclined dense jets with and without swirl. In particular, the experimental results confirmed that SLIF offers valuable visualizations of mixing patterns in complex swirling situations that require three-dimensional volumetric scanning. Moreover, the volumetric measurements also enable the extraction of oblique sections across the inclined dense jet, facilitating the analysis of concentration distributions at various offset planes. This capability is crucial for enhancing the understanding of three-dimensional mixing processes for inclined dense jets particularly with swirl.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143668164","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}

引用次数: 0

A model experiment to study the metal pad roll instability under ambient conditions

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-19 DOI: 10.1007/s00348-025-03973-7

Pranav Hegde, Thomas Gundrum, Gerrit Maik Horstmann

{"title":"A model experiment to study the metal pad roll instability under ambient conditions","authors":"Pranav Hegde, Thomas Gundrum, Gerrit Maik Horstmann","doi":"10.1007/s00348-025-03973-7","DOIUrl":"10.1007/s00348-025-03973-7","url":null,"abstract":"<div><p>We present a new model experiment to study the metal pad roll (MPR) instability, which is a limiting factor for the safe operation of aluminum reduction cells. The idea of our experiment is to replace the horizontal electrical currents in the aluminum layer, which are caused by displacements of the cryolite–aluminum interface in industrial reduction cells, with a synthetic current that is supplied through the side walls of the experimental cell. In this way, only one liquid layer of an electrically conducting fluid is required for modeling the MPR instability, allowing the experiment to operate under ambient conditions using the room-temperature liquid alloy GaInSn as the current-bearing fluid. We demonstrate that the experimental model allows self-amplifying MPR waves to be destabilized and maintained in a reproducible way. The setup is equipped with an acoustic measurement technique that facilitates precise submillimeter measurements of liquid metal surface elevations, which makes it possible to determine several key quantities such as MPR growth rates, stability onsets, saturation amplitudes, or viscous and magnetic damping rates. As the MPR destabilizing Lorentz force synthesized in the experiment can be calibrated to the Lorentz forces appearing in real two-layer cells, the proposed model experiment is intended to establish a novel framework for experimental benchmarking.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03973-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143655219","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}

引用次数: 0

Development and application of a new visualization technique using photochromism for transport process of lubricating oil around the engine piston

IF 2.3 3区工程技术

Experiments in Fluids Pub Date : 2025-03-17 DOI: 10.1007/s00348-025-03997-z

Akihiko Azetsu, Masayuki Ochiai

{"title":"Development and application of a new visualization technique using photochromism for transport process of lubricating oil around the engine piston","authors":"Akihiko Azetsu, Masayuki Ochiai","doi":"10.1007/s00348-025-03997-z","DOIUrl":"10.1007/s00348-025-03997-z","url":null,"abstract":"<div><p>A new visualization technique using photochromism for the movement of oil film was developed and applied to an optical gasoline engine. A photochromic dye was dissolved in the oil and an arbitrary position of the oil film was illuminated by UV laser light, which makes a marker in the oil film via a photochromic reaction. The lifetime of color change by photochromism is relatively long and therefore, by tracking the movement of a marker makes it possible to visualize the movement of oil film directly. The color density was quantified based on the absorbance calculated from images taken before and after coloring in two wavelengths. Through the experimental and theoretical considerations, it was confirmed that the calculated absorbance is effective in reducing a noise originated by the color, the shape of the piston surface, the temporal variation of oil film thickness and the illuminating light intensity distribution. Furthermore, the value of the absorbance is in a very good linear relationship with the oil film thickness. This technique was applied to an optical gasoline engine and confirmed the availability of this technique. In the top land of piston surface, the oil film between the piston and cylinder liner was separated and the majority of the oil is at the piston surface and moved with the piston motion. The oil film thickness on the cylinder liner was very thin. On the contrary, at the piston skirt region, a wider region of the oil film is connected between the linear and the piston skirt. However, there are regions where the oil film between the liner and the skirt is separated by oil film rupture and the majority of the oil film is on the piston skirt. The change of the flow direction by the operating condition, i.e., the throttle condition, was able to clearly visualize, though the movement of oil film on the piston surface was very slow in normal case. The relatively fast complexed flow for opposite direction was also able to visualize by this technique.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143632534","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}

引用次数: 0