Experiments in Fluids最新文献

{"title":"Asymmetric time sequence for multiple-exposure 3D PTV","authors":"Fulvio Scarano,&nbsp;Ilda Hysa,&nbsp;Adrian Grille Guerra,&nbsp;Marthijn Tuinstra,&nbsp;Andrea Sciacchitano","doi":"10.1007/s00348-025-03993-3","DOIUrl":"10.1007/s00348-025-03993-3","url":null,"abstract":"<div><p>Recording onto a single-frame multiple exposures of the tracer particles has the potential to simplify the hardware needed for 3D PTV measurements, especially when dealing with high-speed flows. The analysis of such recordings, however, is challenged by the unknown <i>time tag</i> of each particle exposure, alongside their unknown organization into physical trajectories (<i>trajectory tag</i>). Using a sequence of two or more illumination pulses with a constant time separation leads to the well-known <i>directional ambiguity</i> problem, whereby it is not possible to distinguish the direction of motion of the tracer particles. Instead, an irregular and asymmetric sequence of time separation for the illumination pulses allows recognizing the <i>time tag</i> of the unique sequence of positions in the image, composing the <i>trace</i>. A criterion is formulated here that recognizes unambiguously the <i>trace</i> pattern, based upon the principle of kinematic similarity. A combinatorial algorithm is proposed whereby a signal-to-noise ratio is introduced for every candidate trace. The approach is combined with an additional criterion that favors trace regularity (minimum velocity fluctuations). The algorithm is illustrated making use of particle motion examples. Furthermore, it is assessed using 3D experimental data produced with time-resolved analysis (single-frame, single-exposure) using the <i>Shake-the-Box</i> method. Traces with a three-pulse sequence yield a detection rate of 85%. The latter declines with the number of pulses. Conversely, the error rate rapidly vanishes with the samples number, which confirms the reliability of trace detection criterion when more pulses are comprised in the sequence.</p><h3>Graphical abstract</h3>\u0000<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":"2025-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03993-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143612230","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":"Characteristics-based measurements of supersonic flows from schlieren images","authors":"Alberto Guardone,&nbsp;Marta Zocca,&nbsp;Paolo Gajoni,&nbsp;Francesca Mondonico,&nbsp;Camilla Cecilia Conti","doi":"10.1007/s00348-025-03958-6","DOIUrl":"10.1007/s00348-025-03958-6","url":null,"abstract":"<div><p>A novel method is presented to measure Mach number and flow angle from schlieren images of two-dimensional supersonic flows. A line detection technique is used to extract characteristic lines from schlieren images to measure the velocity direction and the Mach number at the intersection of characteristic curves. The proposed technique is independent of fluid thermodynamics and applies to dilute gas flows and non-ideal compressible flows. The velocity magnitude and fluid thermodynamics are retrieved from the fluid thermodynamic model, assuming constant total enthalpy and entropy. Mach number measurements are also obtained at solid walls by integrating the compatibility equation along the characteristic lines, using the measurements within the flowfield as initial conditions. Results are presented for two exemplary cases: an asymmetric converging–diverging nozzle and the supersonic flow around a diamond-shaped airfoil. Measured values of the Mach number and the flow angle agree with numerical predictions and indirect Mach number measurements based on pressure measurements. The reconstructed pressure and velocity magnitude values agree fairly well with available measurements and simulations in the dilute gas and in the non-ideal regimes.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03958-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143594746","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":"Spatio-temporal characterization of the three-dimensional wave dynamics in falling film flows over rectangular corrugations","authors":"Andrea Düll,&nbsp;Jannick Lehmann,&nbsp;Marion Börnhorst,&nbsp;Cihan Ateş,&nbsp;Thomas Häber,&nbsp;Olaf Deutschmann","doi":"10.1007/s00348-025-03978-2","DOIUrl":"10.1007/s00348-025-03978-2","url":null,"abstract":"<div><p>Falling film flows over rectangular corrugations can exhibit intense time-oscillatory interfacial motion. This is of considerable interest for heat and mass transfer applications, where structured surfaces play a crucial role in process intensification. Our contribution relies on high-speed imaging and image processing based on an internally referenced light absorption method to obtain a full spatio-temporal characterization of the structure-induced wave evolution. After validating the customized experimental technique, particular emphasis is placed on identifying relationships between the steady and transient characteristics of aqueous falling film flows under operating conditions relevant to, e.g., falling film absorbers for <span>(text {CO}_2)</span> capture applications. The transient film instabilities are found to evolve from an initially steady film flow. In the investigated Reynolds number range, inertia-controlled liquid overshoot in wall-normal direction at the structure element’s upstream edges plays a crucial role in the overall flow destabilization. The developed film flow can be decomposed into a steady and a time-oscillatory flow contribution. The former is characterized by a dominant two-dimensional wave shape with a primary wavelength matching that of the bottom contour, while the latter is more isotropic in shape. Nevertheless, both flow contributions are interconnected, with high oscillation intensities being usually accompanied by a strongly sloped steady base flow. In the context of surface structure optimization, the streamwise length scale of the steady interfacial ridge induced at an isolated structure element may serve as a predictor for identifying structure spacings that exhibit particularly strong transient flow destabilization.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03978-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143583541","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":"Characterization of the fractal dimension of helium plumes in laminar to turbulent transition","authors":"Maria N. D’Orazio,&nbsp;Christian Peterson,&nbsp;Michael J. Hargather","doi":"10.1007/s00348-025-04001-4","DOIUrl":"10.1007/s00348-025-04001-4","url":null,"abstract":"<div><p>Schlieren imaging in conjunction with a high-speed camera was used to observe the behavior of metered helium plumes as they transition from laminar to turbulent flow in an air environment. The plumes were visualized at twelve jet Reynolds numbers ranging from 200 to 2980. The fractal dimension of the flows was obtained by applying a box counting algorithm to the recorded schlieren images. The results were analyzed to determine the correlation between the Reynolds number of the flow and the fractal dimension of the observed turbulence. A trend of increasing fractal dimension with increasing Reynolds number was observed for several different types of schlieren cutoffs including horizontal cutoff, vertical cutoff, circular cutoff, focused shadowgraphy and de-focused shadowgraphy. The vertical cutoff and focused shadowgraphy imaging methods showed the most consistent results for the fractal dimension characterization during the laminar to turbulent transition. For transitional plumes, it was observed that fractal dimension increased with distance from the jet outlet.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04001-4.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143570892","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":"Noise reduction measurement and biomimetic propeller optimization designs for unmanned underwater vehicles","authors":"Jialin Liu,&nbsp;Yuqing Hou,&nbsp;Chenxi You,&nbsp;Yong Zou,&nbsp;Chengwang Xiong,&nbsp;Dajing Shang,&nbsp;Pengyu Lv,&nbsp;Hongyuan Li,&nbsp;Huiling Duan","doi":"10.1007/s00348-025-03995-1","DOIUrl":"10.1007/s00348-025-03995-1","url":null,"abstract":"<div><p>Biomimetic microstructured surfaces hold significant potential to alter the characteristics of flow fields and are actively being investigated for their role in noise reduction in the propellers of unmanned underwater vehicles (UUVs). However, accurately measuring the noise generated by UUVs remains a challenge, which complicates the validation of noise reduction strategies and leaves the underlying mechanisms insufficiently understood. In this study, we propose a general noise measurement method for UUVs that involves identifying the main noise sources, designing noise reduction strategies, and validating their effectiveness. Experimental results indicate that the propeller is the main noise source, prompting the design of biomimetic propellers incorporating serrated edges and surface microstructures inspired by humpback whales. These biomimetic propellers are subsequently installed on a UUV for testing, and the results demonstrate a significant noise reduction of up to 6.67 dB. To further validate the noise reduction effects, additional experiments are conducted to measure the motor power consumption and assess the hydrodynamic performance of the different propellers. The motor power consumption is slightly higher for the optimized propellers compared to the original design, indicating that the noise reduction effect can indeed be attributed to the changes in the propeller design, rather than fluctuations in motor performance. Additionally, the characteristic curves of the propellers revealed that while the biomimetic propellers produce lower thrust compared to the original propeller, they maintain stable performance across varying operating conditions. By combining experimental measurements with numerical simulations, we elucidate the underlying noise reduction mechanisms of biomimetic propellers, specifically the breakup of large-scale vortices into smaller, lower-energy vortices. This process reduces the energy of the large-scale vortices and redistributes it over a broader frequency spectrum. These findings provide a robust theoretical and experimental foundation for developing efficient, low-noise underwater propulsion systems, demonstrating profound academic and practical implications.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143564463","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":"A simplified photogrammetry procedure for quantitative on- and off-surface flow topology studies over 3D surfaces: application to a Gaussian bump geometry","authors":"Igal Gluzman,&nbsp;Patrick Gray,&nbsp;Thomas C. Corke,&nbsp;Flint O. Thomas","doi":"10.1007/s00348-025-03970-w","DOIUrl":"10.1007/s00348-025-03970-w","url":null,"abstract":"<div><p>A novel photogrammetry procedure is proposed for projecting 3D surface oil flow visualizations from 2D images over an arbitrary computer-aided design (CAD) model of a 3D surface. The technique yields a 3D view of the oil flow pattern on the model surface from different view angles and allows rendering it along with off-surface particle image velocimetry (PIV) flow field measurements. The technique is based on a recently developed simplified photogrammetry procedure proposed by Gluzman (Exp Fluids 63:118, 2022), which is modified to account for the full, large flow field over the 3D surface. The procedure requires only two reference markers on the given surface geometry CAD model, a small checkerboard placed on a flat surface near the 3D geometry, and a single camera that should capture at least three images after the experiment from any view angle in order to calibrate the projection. The proposed procedure allows removing the elaborate steps typically required in photogrammetry while retaining the same measurement accuracy. In particular, we demonstrate the application of the technique to study turbulent smooth-body flow separation over a Gaussian bump geometry in Gray (Part I-Exp Investig, 2023). Our photogrammetric procedure allows us to obtain a 3D view from different angles of the surface oil flow pattern warped over the CAD model geometry and coupled with stereo PIV plane flow field cuts, which provides important insights into the character of the flow separation.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03970-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143554115","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":"Error-based dynamic velocity range of PIV processing algorithms","authors":"Gauresh Raj Jassal,&nbsp;Bryan E. Schmidt","doi":"10.1007/s00348-025-03998-y","DOIUrl":"10.1007/s00348-025-03998-y","url":null,"abstract":"<div><p>The ability of PIV processing algorithms to accurately determine velocity vectors across the range of motion present in PIV images is characterized by the algorithm’s dynamic velocity range (DVR). Conventionally, the DVR of PIV is defined using the ratio between the maximum and minimum resolvable particle displacements, with the minimum based on the uncertainty in the location of a single particle in the optical system. In this work, it is demonstrated that this definition is inadequate in practice, as it ignores many factors which affect the accuracy of an algorithm when determining small displacements, and the error in vectors with small magnitudes in actual flows is often many times larger than the theoretical minimum. A more useful criterion for determining the DVR of a PIV setup is proposed that depends on conditional errors, using synthetic data to produce a known ground truth. The introduced error-based DVR accounts for the effect of multiple flow velocity scales present in a PIV experiment as well as multi-particle effects. It is found that the practical, error-based DVR of cross-correlation-based PIV is highly experiment-dependent and much lower than the widely accepted value of <span>(mathcal {O} left( {10^2} right))</span>, typically <span>(mathcal {O} left( {10^0} right) - left( {10^1} right))</span>. The findings from the synthetic data results are corroborated using experimental PIV data to approximate the DVR via a deviation-based approach when the ground truth is unknown.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03998-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143553791","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":"An intensified ultra-high-speed optical emission spectroscopy system for hypersonic impulse test facilities","authors":"Nathan H. Lu,&nbsp;Timothy J. McIntyre,&nbsp;Carolyn Jacobs,&nbsp;Andreas Andrianatos,&nbsp;Christopher James","doi":"10.1007/s00348-025-03999-x","DOIUrl":"10.1007/s00348-025-03999-x","url":null,"abstract":"<div><p>This paper provides a comprehensive investigation into creating a spectroscopy system capable of capturing quantitative data that are spatially, spectrally, and temporally resolved, at a minimum of 100 kHz frame rate using an ultra-high-speed camera, a high-speed image intensifier, and a spectrograph. The system was thoroughly tested in a controlled environment using a PhatLight green LED and a Labsphere CSTM-USS400-HI calibration lamp to determine its capabilities and limitations. The sensitivity at different wavelengths and how exposure time and intensifier gain settings affect the sensitivity of the system were evaluated. The system performed well with an exception of a drop in intensity when recording over long periods of time. Upon investigation, it was discovered that the intensifier cannot sustain a constant gain at higher counts for extended lengths of time. The gain drop in the intensifier is minimal for test times less than 200 <span>(mu)</span>s, allowing the system to be operated on short-duration facilities. For test times of milliseconds, the gain drop must be accounted for either in data calibration or analysis. The system proved successful in capturing spectral data at a 100-kHz frame rate on the University of Queensland’s X2 free-piston driven expansion tube, when investigating contamination in the facility. The ultra-high-speed intensified optical emission spectroscopy system allowed for spectral data that were spatially, spectrally, and temporally resolved in a short-duration hypersonic impulse testing facility, giving a better understanding of interactions and phenomena occurring in radiating flow.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 4","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03999-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143554114","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":"High-speed droplet impact on solid surfaces: review on the prospects of modeling fluid flow","authors":"I. S. Vozhakov,&nbsp;S. Y. Misyura,&nbsp;V. S. Morozov,&nbsp;M. V. Piskunov,&nbsp;A. E. Piskunova,&nbsp;E. G. Orlova,&nbsp;R. I. Mullyadzhanov","doi":"10.1007/s00348-025-03996-0","DOIUrl":"10.1007/s00348-025-03996-0","url":null,"abstract":"<div><p>This paper provides a comprehensive review of promising areas in the development and application of methods for predicting the high-speed droplet impact on a solid wall. The development of such methods is critically essential for solving a wide range of engineering problems from the point of view of maximum approximation to real working conditions. For example, the erosion of wind turbine blades and solar cell surfaces from wind and water droplets causes significant economic damage each year and reduces the lifetime of alternative energy technologies and equipment. The review analyzes a wide range of problems related to droplet-wall impact at high Weber numbers and droplet propagation on textured surfaces with inhomogeneous wettability: experimental methods, analytical approaches and numerical models, as well as their prospects and limitations.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 3","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-03-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143530000","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":"Vortex force map method to estimate unsteady forces from snapshot flowfield measurements","authors":"Shūji Ōtomo,&nbsp;Pascal Gehlert,&nbsp;Holger Babinsky,&nbsp;Juan Li","doi":"10.1007/s00348-025-03962-w","DOIUrl":"10.1007/s00348-025-03962-w","url":null,"abstract":"<div><p>An accurate non-intrusive force measurement is challenging in many situations, especially those involving animals and vehicles. This paper reports a non-intrusive technique based on the vortex force map (VFM) method, which computes forces from snapshot velocity and vorticity fields obtained from the particle image velocimetry (PIV) flow measurement. This study is the first application of the VFM method to PIV velocity data. The VFM method is applied to three different kinematic families for surging flat plates and pitching NACA 0018 aerofoils at Reynolds numbers of <span>({ mathcal {O}left( {10^{4}}right) })</span>, where flowfields are characterised by massive flow separation with the shedding of the coherent leading-edge and trailing-edge vortices. In all three cases, we observe an agreement between the direct force measurements and the VFM method even if a relatively small region around aerofoils is captured for PIV. Moreover, physical explanations of the linkage between the forces and vortical structures are provided based on the visualised force contribution of each vortex. The VFM method is highly robust to noise (a significant feature in experimental fluid mechanics) and can be applied to snapshot data.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 3","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-02-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03962-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143521785","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}