Experiments in Fluids最新文献

{"title":"Exploring separation and reattachment in shear-thinning suspensions through pipe-wall ultrasound measurements","authors":"Giuseppe Rosi,&nbsp;Moira Barnes,&nbsp;Frieder Kaiser,&nbsp;David Rival","doi":"10.1007/s00348-025-04018-9","DOIUrl":"10.1007/s00348-025-04018-9","url":null,"abstract":"<div><p>To better understand how turbulent flow structures develop within shear-thinning suspensions (STSs), we investigate the behavior of a shear layer forming within an STS downstream of a sudden expansion with an expansion ratio of 0.5. Specifically, the shear-layer reattachment behavior downstream of an axisymmetric expansion is characterized through ultrasound imaging velocimetry (UIV) and through pressure measurements, and the observed behavior is used to surmise how the shear layer is modified within the STS. Four fluids are investigated, which include pure water, as well as three 1750 ppm xanthan-gum-in-water solutions mixed with non-reactive mineral microspheres at volume fractions of 0%, 15%, and 30%. Wall-pressure measurements were collected through pressure taps located at 0<i>h</i> to 25.8<i>h</i> downstream of the expansion with subsequent UIV measurements collected from 1<i>h</i> to 9<i>h</i> downstream of the expansion, where <i>h</i> is the step height and equals the difference between the pipe and throat radii. For single-phase cases, pressure-recovery profiles and UIV flow fields indicate a predictably large reattachment length at low Reynolds numbers, which shortens as the Reynolds number increases from <span>(O(10^2))</span> to <span>({O}(10^4))</span> and finally stabilizes at roughly 8<i>h</i>. In contrast, the STSs exhibit pressure-recovery and pipe-wall velocity profiles indicating a reattachment length that is consistently short (8<i>h</i>) and independent of Reynolds number. The results indicate that the suspended phase within the STSs causes the shear layer to diffuse far more rapidly, thereby promoting momentum transfer toward the wall, which results in a consistently short reattachment length.</p><h3>Graphic 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 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04018-9.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143892675","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":"Experimental study on bubble pairs and induced flow fields using tomographic particle image velocimetry","authors":"Hanbin Wang,&nbsp;Yang Xu,&nbsp;Jinjun Wang","doi":"10.1007/s00348-025-04026-9","DOIUrl":"10.1007/s00348-025-04026-9","url":null,"abstract":"<div><p>Owing to their unique fluid dynamics, gas‒liquid two-phase flows, such as bubbly flows, are widely used in various engineering applications. This study utilized three-dimensional shadow image reconstruction (3D-SIR) and laser-induced fluorescence tomographic particle image velocimetry (LIF-TPIV) to perform a quantitative analysis of the three-dimensional morphology and motion of bubbles, as well as bubble-induced flow fields. By systematically varying the orifice spacing (<span>(s/{D}_{n})</span>, where <span>({D}_{n})</span> is the orifice inner diameter) among the values 3.3, 5, 6.7, and 8.3, we investigate the effects of distance on bubble interactions and flow dynamics. Our findings reveal that at <span>(s/{D}_{n})</span> = 3.3, the bubbles move very close to each other while rising. Distinct vortex rings form around each bubble near the orifice and merge as they rise, which increases flow transport, dissipation, and flow velocity between bubbles, leading to earlier bubble instability. Spectral analysis indicates that bubble spacing is coupled with the dominant flow frequency. As orifice spacing increases, bubble interactions weaken, resulting in independent vortex rings near the orifice that grow to approximately twice the bubble’s diameter before shedding secondary vortices. In these cases, regions of strong transport and dissipation are concentrated in the wake, and the flow velocity between bubbles remains relatively weak. Bubble instability primarily originates from the wake vortices. The aspect ratios of the bubbles align with the dominant flow frequency, indicating a coupling between flow dynamics and bubble morphology, although periodicity in bubble spacing weakens at larger spacings. These findings provide valuable insights into two-phase flow dynamics, especially in multiorifice bubbly flows. </p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143883609","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":"Synthetic jet vortex rings impinging onto porous walls: a more comprehensive similarity parameter","authors":"Yang Xu,&nbsp;Haocheng Wang,&nbsp;Congyi Xu,&nbsp;Zhiyu Li,&nbsp;Jinjun Wang","doi":"10.1007/s00348-025-04023-y","DOIUrl":"10.1007/s00348-025-04023-y","url":null,"abstract":"<div><p>By combining the effects of synthetic jet Reynolds number (<i>Re</i>_<i>sj</i>), porous wall porosity (<i>ϕ</i>) and porous wall hole diameter (d_<i>h</i>*), Li et al. (AIAA J 58:722–732, 2020) and Xu et al. (Phys Fluids 33:035140, 2021) presented a dimensionless similarity parameter [(<i>Re</i>_<i>sj</i>²<i>d* </i>_<i>h</i>³)^<i>ϕ</i>] to characterize the interaction between synthetic jet vortex rings and a porous wall. To futher incorporate the jet-exit-to-wall distance (<i>H</i>^*) into this similarity parameter, an experimental study was conducted to inverstigate the effect of the jet-exit-to-wall distance (<i>H</i>^* = 2, 4, 6, and 8) on the impingement of synthetic jet vortex rings onto a porous wall under three Reynolds numbers (<i>Re</i>_<i>sj</i> = 300, 600, and 900). By establishing the relationship between the loss of jet momentum flux and the jet-exit-to-wall distance (<i>H</i>^*) at different <i>Re</i>_<i>sj</i>, a more comprehensive similarity parameter [(<i>Re</i>_<i>sj</i>²<i>d</i>_<i>h</i>^<i>*</i>3<i>H</i>^*−0.64)^<i>ϕ</i>] was derived to characterize this vortex rings-porous wall interaction. Given the substantial impact of <i>H</i>^* on the vortex ring strength upon the impingement, an effective interaction velocity (<i>V</i>_<i>j,eff</i> = <i>V</i>_<i>j</i>/<i>H</i>^*0.32±0.045, <i>V</i>_<i>j</i> is the characteristic velocity of the synthetic jet) was introduced, so that [(<i>Re</i>_<i>sj</i>²<i>d</i>_<i>h</i>^<i>*</i>3<i>H</i>^*−0.64)^<i>ϕ</i>] was transformed as [(<i>Re</i>_<i>eff</i>²<i>d</i>_<i>h</i>^<i>*</i>)^<i>ϕ</i>], where <i>Re</i>_<i>eff</i> was the Reynolds number based on <i>V</i>_<i>j,eff</i>. This new similarity parameter effectively characterized both the losses of the momentum flux and kinetic energy transport due to impinging onto a porous wall in over 50 cases from current and previous experiments, thus verifying its validity at least in the range of [(<i>Re</i>_<i>eff</i>²<i>d</i>_<i>h</i>^<i>*</i>)^<i>ϕ</i>] ≤ 1000.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143850932","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":"Simultaneous measurements of velocity, oxygen concentration, and deformed interface position in an air–water channel using PIV and LIF","authors":"Adharsh Shankaran,&nbsp;R. Jason Hearst","doi":"10.1007/s00348-025-04017-w","DOIUrl":"10.1007/s00348-025-04017-w","url":null,"abstract":"<div><p>Oxygen transfer across a deforming air–water interface is studied using a synergy of particle image velocimetry and laser-induced fluorescence (LIF). Such approaches have previously been limited to flat interfaces. We develop simultaneous measurements of velocity fields, dissolved oxygen (DO) concentration fields, and interface positions for spatial and temporal tracking. The imaging process begins after the DO in the water has been chemically depleted and continues until the water is saturated with DO. The oxygen LIF intensity field is calibrated using measurements from an optical oxygen probe to ensure accurate conversion into physical unit (mg/L). A canonical air turbulent channel flow, with a centerline velocity of 6.6 m/s (Reynolds number based on channel height of 21,700), develops for more than 100 heights before the bottom boundary condition is changed from a solid wall to a water surface. This induces transient and wavy structures on the air–water interface and generates velocity fluctuations and vorticity on the water side, which drives DO transport. The spatial evolution of DO concentration reveals steep gradients near the interface that diminish with depth, while the temporal evolution shows a reduction in concentration differences between the bulk and interface from about 35% to less than 5% as the water saturates. Concentration fluctuations are lower near the interface compared to the bulk and diminish in time as the system approaches saturation. Turbulent scalar transport analysis shows high vertical flux near the interface, and this too changes as the bulk DO concentration evolves, emphasizing that the observed phenomena are transient and should be treated as such.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04017-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143848987","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 propagation of direct pressure gradient integration and a Helmholtz–Hodge decomposition-based pressure field reconstruction method for image velocimetry","authors":"Lanyu Li,&nbsp;Jeffrey McClure,&nbsp;Grady B. Wright,&nbsp;Jared P. Whitehead,&nbsp;Jin Wang,&nbsp;Zhao Pan","doi":"10.1007/s00348-025-03991-5","DOIUrl":"10.1007/s00348-025-03991-5","url":null,"abstract":"<div><p>Recovering pressure fields from image velocimetry measurements has two general strategies: (i) directly integrating the pressure gradients from the momentum equation and (ii) solving or enforcing the pressure Poisson equation (divergence of the pressure gradients). In this work, we analyze the error propagation of the former strategy and provide some practical insights. For example, we establish the error scaling laws for the pressure gradient integration (PGI) and the pressure Poisson equation. We explain why applying the Helmholtz–Hodge decomposition (HHD) could significantly reduce the error propagation for the PGI. We also propose to use a novel HHD-based pressure field reconstruction strategy that offers the following advantages or features: (i) effective processing of noisy scattered or structured image velocimetry data on a complex domain; (ii) using radial basis functions (RBFs) with divergence/curl-free kernels to provide divergence-free correction to the velocity fields for incompressible flows and curl-free correction for pressure gradients; and (iii) enforcing divergence/curl-free constraints without using Lagrangian multipliers. Complete elimination of divergence-free bias in measured pressure gradient and curl-free bias in the measured velocity field results in superior accuracy. Synthetic velocimetry data based on exact solutions and high-fidelity simulations are used to validate the analysis as well as demonstrate the flexibility and effectiveness of the RBF-HHD solver.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143822024","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":"Super-temporal global reconstruction of convective disturbances from images of two-dimensional flows","authors":"Cole Sousa,&nbsp;Stuart Laurence","doi":"10.1007/s00348-025-04015-y","DOIUrl":"10.1007/s00348-025-04015-y","url":null,"abstract":"<div><p>A method for converting spatial data from high-speed schlieren visualizations into upsampled temporal data, previously limited to applications involving fluid flows with uniform-velocity disturbances, is extended to flows with variable-velocity disturbances. Schlieren-based velocimetry is first employed to derive disturbance propagation speeds and directions throughout the schlieren field of view. The velocity field is then integrated to determine disturbance streamlines through discrete pixel locations, permitting reconstructions of the temporal signal at times between schlieren images. The resulting temporal signals have an effective sampling rate governed by the spatial resolution of the images, rather than the camera frame rate, with the local propagation speeds providing the necessary conversion to temporal units. The efficacy of the method is demonstrated by applying it to a schlieren dataset capturing Mach 6 flow over a cone–flare model with a frame rate of 824 kHz. The frame rate is sufficient to resolve the relevant second-mode disturbances from the raw pixel times series, allowing for quantitative comparisons between the raw and reconstructed signals. The reconstruction process enhances the information extractable from the temporal signals by eliminating aliased content previously constrained by the camera’s Nyquist frequency and enabling the analysis of additional high-frequency content. The accuracy and robustness of the reconstruction are validated by introducing known errors into the signals. Increased camera frame rates correlate with improved robustness, with errors in propagation speed of up to <span>(pm 10%)</span> having minimal impact on the spectral characteristics of the signal for frame rates as low as approximately half the primary disturbance frequency.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04015-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143818308","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":"Free surface topography of capillary flows using spatiotemporal phase shifting profilometry","authors":"Hélie de Miramon,&nbsp;Wladimir Sarlin,&nbsp;Axel Huerre,&nbsp;Pablo Cobelli,&nbsp;Thomas Séon,&nbsp;Christophe Josserand","doi":"10.1007/s00348-025-04006-z","DOIUrl":"10.1007/s00348-025-04006-z","url":null,"abstract":"<div><p>We present a novel experimental technique for characterizing the free surface of capillary flows using the spatiotemporal phase shifting profilometry (ST-PSP) method. This study specifically addresses various regimes of capillary flows over inclined surfaces, including drops, rivulets, meanders, and braided films. The technique is explained step by step with a detailed discussion of the calibration process, which is carried out on a solid wedge to determine the optical distances required for the phase-to-height relationship. In addition, the minimal dye concentration for accurately reconstructing the free surface of a dyed water flow is investigated. The ST-PSP method is then applied to profile different liquid flows, achieving large signal-to-noise ratios in all experiments. Notably, the analysis of a sessile droplet shows excellent agreement between the ST-PSP results and side-view visualizations, as demonstrated by the precise recovery of its apparent contact angle. Moreover, free surface reconstructions of rivulet flows align well with previous theoretical predictions. These findings suggest that the ST-PSP method is highly effective for obtaining precise height maps of capillary flows, offering a valuable tool for future validation of theoretical models.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143809095","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":"Influence of backward-facing steps on laminar-turbulent transition in two-dimensional boundary layers at subsonic Mach numbers","authors":"Steffen Risius,&nbsp;Marco Costantini","doi":"10.1007/s00348-025-03994-2","DOIUrl":"10.1007/s00348-025-03994-2","url":null,"abstract":"<div><p>Backward-facing steps (BFS) can have a detrimental impact on laminar flow lengths because of their strong effect on boundary layer transition. BFS with normalized step heights in the range of <span>(h/delta _1 approx)</span> 0.1 to 0.6 (corresponding to height-based Reynolds numbers of <span>(hbox{Re}_h = (U_infty h / nu ) approx)</span> 230 to 2430) were installed in a two-dimensional wind tunnel model and tested in the Cryogenic Ludwieg-Tube Göttingen, a blow-down wind tunnel with good flow quality. The influence of BFS on the location of laminar-turbulent transition was investigated over a wide range of unit Reynolds numbers from <span>(hbox{Re}_1 = {17.5times 10^{6},{text {m}^{-1}}})</span> to <span>(80times 10^{6},hbox{m}^{-1})</span>, three Mach numbers, <span>(M= 0.35)</span>, 0.50 and 0.65, and various streamwise pressure gradients. The measurement of the transition locations was accomplished non-intrusively by means of temperature-sensitive paint. Transition Reynolds numbers, calculated with the flow length up to the location of laminar-turbulent transition <span>(x_{T})</span>, ranged from <span>(hbox{Re}_{rm tr}approx)</span> 1 × 10⁶ to 11 × 10⁶, and were measured as a function of step height, pressure gradient, Reynolds and Mach numbers. Incompressible linear stability analysis was used to calculate amplification rates of Tollmien–Schlichting waves; transition <i>N</i>-factors were determined by correlation with the measured transition locations. In parallel to earlier investigations with a similar setup, this systematic approach was used to identify functional relations between non-dimensional step parameters (<span>(h/delta _1)</span> and <span>(hbox{Re}_h)</span>) and the relative change of the transition location. Furthermore, the change of the transition <i>N</i>-factor <span>(Delta N)</span> due to the installation of the steps was investigated. It was found that the installation of backward-facing steps with <span>(h/delta _1 lesssim 0.15)</span> and <span>(hbox{Re}_h lesssim 300)</span> does not lead to a reduction of <span>(hbox{Re}_{rm tr})</span> and to <span>(Delta N &gt; 0)</span>. However, increasing the step size results in a decreasing laminar flow length and thus an increasing <span>(Delta N)</span>. The reported results are in general agreement with earlier investigations at significantly lower Mach and Reynolds numbers.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-03994-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143809286","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":"On the unsteady aerodynamics of a surging airfoil at (90{^circ }) incidence","authors":"Guanqun Xu,&nbsp;Andrea Sciacchitano,&nbsp;Carlos Ferreira,&nbsp;Wei Yu","doi":"10.1007/s00348-025-04011-2","DOIUrl":"10.1007/s00348-025-04011-2","url":null,"abstract":"<div><p>Wind turbine blades in standstill or parked conditions often experience large angles of attack (AoA), where vortex-induced vibrations (VIV) may occur that increase the risk of structural damage. To better understand the VIV of airfoils at high AoA from an aerodynamic perspective, we conducted experimental investigations into the vortex dynamics of a surging airfoil at a <span>(90^circ)</span> incidence undergoing forced vibrations. Experiments were conducted at two reduced frequencies (<i>k</i>) to demonstrate the lock-in effect, where the vortex shedding frequency aligns with the motion frequency. Results indicate distinct vortex shedding behaviors: at higher <i>k</i> value of 0.38, downstream wake vortices form when the airfoil is moving upwind, while upstream vortices emerge during the downwind motion, interacting with the downstream vortices and leading to an outward flow. At lower <i>k</i> value of 0.19, the wake remains directed to the downwind side, regardless of the airfoil’s motion direction. Lock-in is evident in both cases, with one vortex pair shed per cycle at lower <i>k</i> and two pairs at higher <i>k</i>. Furthermore, the study examines the influence of vortex dynamics on unsteady aerodynamic loads. The results show that drag peaks when the airfoil moves upwind near the center position of its trajectory; at higher <i>k</i>, negative drag occurs as the airfoil moves downwind near the center, driven by the interactions among convection, turbulent momentum, pressure, and viscous forces. A reduced-order load estimation model for a flat plate is applied to the experimental data, showing good agreement during the upwind motion of the airfoil, which is the design condition for the original flat plate model. However, during the downwind motion, as the flow condition does not match the original flat plate design condition, the circulatory part of the model is modified to account for the presence of two pairs of vortices in the flow field, yielding improved agreement with the drag values determined from the measured flow field. The findings highlight distinct flow patterns and vortex interactions for the two motion cases, offering insights into their impact on aerodynamic loads.</p></div>","PeriodicalId":554,"journal":{"name":"Experiments in Fluids","volume":"66 5","pages":""},"PeriodicalIF":2.3,"publicationDate":"2025-04-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s00348-025-04011-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143793264","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":"Elliptic synthetic jet vortex rings impinging onto a solid wall: effect of Reynolds number","authors":"Guoan Wen,&nbsp;Lei Wang,&nbsp;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>_<i>sj</i> = 318, 477, and 636) are investigated while maintaining a constant orifice-to-wall distance (<i>H</i>₀/<i>D</i>₀ = 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}