Journal of Fluids and Structures最新文献

{"title":"Tip shape effects on the axial-flow-induced vibration of a cantilever rod","authors":"Hao Li ,&nbsp;Andrea Cioncolini ,&nbsp;Shanying Zhang ,&nbsp;Hector Iacovides ,&nbsp;Mostafa R.A. Nabawy","doi":"10.1016/j.jfluidstructs.2024.104132","DOIUrl":"10.1016/j.jfluidstructs.2024.104132","url":null,"abstract":"<div><p>The influence of tip shape on flow-induced vibration of a cantilever rod subjected to axial water flow is experimentally investigated, through optical tracking of the rod movement and mapping of the instantaneous flow field around the rod tip. The experimental setup consists of a vertical cantilever rod housed within a tube. The rod tip shapes considered in this study include a blunt tip and cones with height-to-diameter ratios of 0.5, 1, and 2. The experiments were conducted across a Reynolds number range between 20k to 100k in both clamped-free and free-clamped configurations, representing opposite flow directions. The rod tip motion was captured using fast video image tracking, whereas the flow field near the rod tip was obtained using particle image velocimetry (PIV). The rod vibration dynamics exhibited a primarily fuzzy period-1 behavior, characterized by a periodic motion with a chaotic component. Flutter-like oscillation and buckling were also observed at higher Reynolds numbers, depending on the flow direction. The mechanisms of fluid-structure interaction involved turbulent buffeting and movement-induced excitations. Unsteady flow separation around the rod tip was identified as a further contributing mechanism to flow excitation. In the clamped-free configuration, unsteady flow separation was more pronounced for the cone tips due to the increased rod surface area in the wake region, leading to larger vibration amplitude. In the free-clamped configuration, flow separation effects were more prominent for the blunt tip, as the streamlined cone shapes were less prone to flow separations. Overall, the rod with a blunt tip resulted in smaller displacement in the clamped-free configuration, while the rods with cone tips led to smaller displacement in the free-clamped configuration.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104132"},"PeriodicalIF":3.6,"publicationDate":"2024-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0889974624000677/pdfft?md5=858e530e0235b2163e2ec0d38521d860&pid=1-s2.0-S0889974624000677-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141190020","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Aerodynamics of flapping wings with passive and active deformation","authors":"Florian Bouard ,&nbsp;Thierry Jardin ,&nbsp;Laurent David","doi":"10.1016/j.jfluidstructs.2024.104139","DOIUrl":"10.1016/j.jfluidstructs.2024.104139","url":null,"abstract":"<div><p>This paper reports direct numerical simulations of the flow past rigid and flexible flapping wings under hovering flight conditions. Both passive and active deformations are considered. It is shown that passive deformation can help increase aerodynamic performance through significant wing bending. Bending occurs at the frequency of the prescribed flapping motion and is, in this case, characterized by moderate amplitude and phase lag with respect to the prescribed flapping motion. Bending is then actively prescribed (rather than being a result of passive deformation) with varying phase lag. This allows to decouple the role of bending amplitude and phase lag on aerodynamic performance of the flapping wing. It is shown that both lift and efficiency can be significantly enhanced for phase lags around <span><math><mrow><mn>3</mn><mi>π</mi><mo>/</mo><mn>2</mn></mrow></math></span> but this enhancement reduces with increasing pitch angle. The influence of morphing on aerodynamic performance can be explained by the concomitant role of quasi-steady and unsteady effects. These results hence demonstrate that morphing can be beneficial to the aerodynamics of flapping wings. Furthermore, they can help define structural properties that promote aerodynamic performance of flapping wings through passive deformations (with relevant amplitude and phase).</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"128 ","pages":"Article 104139"},"PeriodicalIF":3.6,"publicationDate":"2024-05-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141189876","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Controlling the chaotic wake of a flapping foil by tuning its chordwise flexibility","authors":"Chhote Lal Shah ,&nbsp;Dipanjan Majumdar ,&nbsp;Chandan Bose ,&nbsp;Sunetra Sarkar","doi":"10.1016/j.jfluidstructs.2024.104134","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104134","url":null,"abstract":"<div><p>Effects of chord-wise flexibility as an instrument to control chaotic transitions in the wake of a flexible flapping foil have been studied here using an immersed boundary method-based in-house fluid–structure-interaction solver. The ability of the flapping foil at an optimum level of flexibility to inhibit chaotic transition, otherwise encountered in a similar but rigid configuration, has been highlighted. The rigid foil manifests chaotic transition through a quasi-periodic-intermittency route at high dynamic plunge velocities; whereas, increasing the level of flexibility gradually regularises the aperiodic behaviour through a variety of interesting wake patterns. If flexibility is increased beyond an optimum level, aperiodicity sets in again and robust chaos is restored at very high flexibility levels. The mechanisms of triggering the order-to-chaos transition are different between the rigid and the high flexibility cases. Along the route to order and back to chaos, the flexible foil exhibits different flow-field behaviours, including far-wake switching, primary &amp; secondary vortex streets, bifurcated wakes and interactive vortices between the bifurcated wakes. The underlying interaction mechanisms of the flow-field vortices responsible for the associated dynamical signatures of the wake have been closely tracked. This study further examines the optimum propulsive performance range of the flexible flapper and investigates its connection with the periodicity/regularity of the system.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104134"},"PeriodicalIF":3.6,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141163664","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydroelasticity effects induced by a single cavitation bubble collapse","authors":"Hemant J. Sagar ,&nbsp;Ould el Moctar","doi":"10.1016/j.jfluidstructs.2024.104131","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104131","url":null,"abstract":"<div><p>To investigate hydroelasticity effects on a single cavitation bubble dynamic, a focused laser was used to generate the bubble in water near a flexible aluminium foil fixed to a specimen holder with a circular aperture to allow the foil to vibrate. The bubble was generated below the foil's center. A laser-based optical sensor measured the displacement at the center of the foil. Simultaneously, a high-speed camera monitored the bubble's dynamics to correlate it with the foil's displacement. By directly measuring the foil's displacements, we provided building block missing in previous investigations. We found that a key difference between bubble dynamics near a rigid and an elastic structure was that, at relative wall distances larger or equal to unity, the bubble did not collapse on the elastic foil. The bubble's dynamics caused dominant foil displacements during its first growth (after plasma seeding) and during its subsequent collapse. Foil displacements during the bubble's first collapse were about twice as large as those during its growth phase. For lower relative wall distances, the induced foil displacements were significant until the bubble's third collapse. At larger relative wall distances, the bubble did not collapse on the elastic foil and, thus, it did not induce erosion. However, it caused foil vibrations and, therefore, may contribute to the foil's structural fatigue damage. Our study postulates that the cavitation may not be erosive, however it can induce impulsive loads causing vibrations and thereby fatigue damage of nearby structures.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104131"},"PeriodicalIF":3.6,"publicationDate":"2024-05-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0889974624000665/pdfft?md5=7f7074d4d5e4303315121fded4000b3a&pid=1-s2.0-S0889974624000665-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141163654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"Bandgap accuracy and characteristics of fluid-filled periodic pipelines utilizing precise parameters transfer matrix method","authors":"Wenjie Li,&nbsp;Xiangxi Kong,&nbsp;Qi Xu,&nbsp;Ziyu Hao","doi":"10.1016/j.jfluidstructs.2024.104136","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104136","url":null,"abstract":"<div><p>The phononic crystal theory provides a novel approach for effectively controlling the bending vibrations in fluid-filled pipelines. This paper innovatively proposes the precise parameters transfer matrix method to investigate the band calculation accuracy and bandgap characteristics of fluid-filled periodic pipelines with various beam types. Firstly, the differential equations for bending vibration of fluid-filled pipelines are established based on deformation and force analysis. The parameters of the system state are precisely represented by the structural form of multiplying the constitutive matrix with the derivative matrix. Combined with Bloch's theorem, the novel precise parameters transfer matrix method for calculating the band structure is proposed. Secondly, the validity of this method is verified through a comparison with finite element simulation results. A detailed analysis is provided regarding the mechanism of bandgap formation and the effect of fluid filling on the band structure. Then, the influence of shear deformation, moment of inertia, and their coupling on the band calculation accuracy for fluid-filled periodic pipelines is studied based on various beam theories. Finally, it delves into the bandgap characteristics of fluid-filled periodic pipelines under different material parameters, structural parameters, and excitation conditions. This research offers valuable insights for the structural design and vibration damping application in fluid-filled periodic pipelines, providing theoretical support for accurately determining their bandgaps.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104136"},"PeriodicalIF":3.6,"publicationDate":"2024-05-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141097268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aeroacoustic effect of boundary layer separation control by rod vortex generators on the DU96-W-180 airfoil","authors":"Thanushree Suresh ,&nbsp;Pawel Flaszynski ,&nbsp;Alejandro Rubio Carpio ,&nbsp;Marcin Kurowski ,&nbsp;Michal Piotrowicz ,&nbsp;Oskar Szulc","doi":"10.1016/j.jfluidstructs.2024.104133","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104133","url":null,"abstract":"<div><p>An experimental campaign to study the impact of a distinct type of vortex generator — rod type (RVG), on the flow characteristics and the acoustic far-field pressure of a wind turbine airfoil, is conducted. Airfoils exhibit decreased aerodynamic performance at high inflow angles due to turbulent boundary layer flow separation. RVGs are applied to mitigate the flow separation. However, this benefit is accompanied by an acoustic penalty. An assessment of the impact of RVGs on the far-field noise emission is conducted for the DU96-W-180 airfoil. The evolution of the boundary layer impacted by the rods is analyzed through Particle Image Velocimetry (PIV) measurements. The resulting reduction in the separation zone is observed through oil flow visualization. Analysis of the sound spectrum for airfoils with/without RVGs is conducted for a range of frequencies (300 Hz to 4000 Hz). Results show a reduction of the noise level at relatively low frequencies, at the expense of an increased noise level in the mid-high frequency ranges. While the former is caused by the reduction of the flow separation, the latter is determined by the combined contribution of the noise scattered by the RVG and by the change in boundary layer characteristics at the airfoil trailing edge.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104133"},"PeriodicalIF":3.6,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141090655","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Identification of low-wavenumber wall pressure field beneath a turbulent boundary layer using vibration data","authors":"Hesam Abtahi ,&nbsp;Mahmoud Karimi ,&nbsp;Laurent Maxit","doi":"10.1016/j.jfluidstructs.2024.104135","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104135","url":null,"abstract":"<div><p>Although the most energetic part of the wall pressure field (WPF) beneath a turbulent boundary layer (TBL) is within the convective region, this region is mostly filtered out by the structure when excited by a low Mach number turbulent flow. Therefore, structural vibration is primarily induced by the low-wavenumber components of the WPF. This highlights the importance of an accurate estimation of the low-wavenumber WPF for predicting flow-induced vibration of structures. Existing semi-empirical TBL models for the WPF agree well in the convective region but significantly differ from one another in estimating the low-wavenumber levels. In this study, we aim to investigate the feasibility of estimating the low-wavenumber WPF by analyzing vibration data from a structure excited by a TBL. The proposed approach is based on the relationship between the TBL forcing function and structural vibrations in the wavenumber domain. By utilizing vibration data obtained from a structure excited by a TBL and incorporating the sensitivity functions of the respective structure, it is possible to estimate the cross-spectrum density of the pressure fluctuations in the wavenumber domain. To demonstrate the effectiveness of the proposed method, an analytical model of a simply-supported panel excited by a reference TBL model is employed. The vibration data of the panel is then used in an inverse method to identify the low-wavenumber levels of the pressure fluctuations, which are then compared to those of the reference TBL model. The performance of the proposed method is examined through a parametric study and virtual experiments.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104135"},"PeriodicalIF":3.6,"publicationDate":"2024-05-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.sciencedirect.com/science/article/pii/S0889974624000707/pdfft?md5=a708e02becc4171cb57c926d3beb4fd4&pid=1-s2.0-S0889974624000707-main.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141090656","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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":"The experimental investigation on wake dynamics of flow around a circular cylinder with the splitter plate","authors":"Jiankang Zhou ,&nbsp;Xiang Qiu ,&nbsp;Jiahua Li ,&nbsp;Bofu Wang ,&nbsp;Quan Zhou ,&nbsp;Yulu Liu","doi":"10.1016/j.jfluidstructs.2024.104130","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104130","url":null,"abstract":"&lt;div&gt;&lt;p&gt;The wake dynamics of flow around a circular cylinder with the splitter plate are investigated using particle image velocimetry (PIV). The Reynolds number based on the cylinder diameter &lt;span&gt;&lt;math&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; is &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;R&lt;/mi&gt;&lt;mi&gt;e&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;3.9&lt;/mn&gt;&lt;mspace&gt;&lt;/mspace&gt;&lt;mo&gt;×&lt;/mo&gt;&lt;msup&gt;&lt;mrow&gt;&lt;mn&gt;10&lt;/mn&gt;&lt;/mrow&gt;&lt;mn&gt;3&lt;/mn&gt;&lt;/msup&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, and the ratio of the splitter plate length &lt;span&gt;&lt;math&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;/math&gt;&lt;/span&gt; on the cylinder diameter varies from &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; to &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;2.5&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. The wake characteristics and vortex dynamics are strongly dependent on &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. There are main and secondary recirculation regions behind the cylinder, and the range of the recirculation region presents an obvious increase as &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; increases from 0 to 1 due to the elongations of the cylinder shear layers. Moreover, the maximum velocity defect and the wake width are increased with increasing &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, and the short splitter plate has important influences on the wake characteristics for &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;. Based on the vortex dynamics, the splitter plate length can be divided into three regions. (i) For &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, the shear layers elongate downstream further to form Karman vortex sheets as &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; increases, and the wake vortices induce formation of the secondary vortex on the trailing edge of the plate. (ii) For &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;mo&gt;≤&lt;/mo&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;&lt;&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, the secondary vortex moves upstream along the plate and gradually lifts up, and the wake vortices are easily broken into some small-scale vortices due to the disturbance of the plate. (iii) For &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;≥&lt;/mo&gt;&lt;mn&gt;2&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, the wake vortices are reattached on the plate, and the secondary vortex is mainly distributed behind the cylinder. The Strouhal number &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; decreases nearly by 26.34 % from &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0.205&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; at &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; to &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;0.151&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; at &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;L&lt;/mi&gt;&lt;mo&gt;/&lt;/mo&gt;&lt;mi&gt;D&lt;/mi&gt;&lt;mo&gt;=&lt;/mo&gt;&lt;mn&gt;1&lt;/mn&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt;, and &lt;span&gt;&lt;math&gt;&lt;mrow&gt;&lt;mi&gt;S&lt;/mi&gt;&lt;mi&gt;t&lt;/mi&gt;&lt;/mrow&gt;&lt;/math&gt;&lt;/span&gt; presents an ","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104130"},"PeriodicalIF":3.6,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141090654","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"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 frequency-independent second-order framework for the formulation of experimental fluidelastic forces using hidden flow variables","authors":"J. Antunes ,&nbsp;P. Piteau ,&nbsp;X. Delaune ,&nbsp;R. Lagrange ,&nbsp;D. Panunzio","doi":"10.1016/j.jfluidstructs.2024.104127","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104127","url":null,"abstract":"<div><p>The importance of fluidelastic forces in flow-excited vibrations is crucial, in view of their damaging potential. Flow-coupling coefficients are often experimentally obtained from vibration experiments, performed within a limited experimental frequency range. For any given flow velocity, these coefficients are typically frequency-dependent, as amply documented in the literature since the seminal work of Tanaka and Takahara. Such frequency dependence, which seems quite natural in view of the flows intricacies, not only is awkward for attempting physical interpretations, but also leads to numerical difficulties when performing time-domain computations. In this work, we address this problem by assuming that the measured fluidelastic forces encapsulate \"hidden\" (non-measured) dynamics of the coupled flow. This leads to the possibility of modelling the flow-structure coupled dynamics through conventional ordinary differential equations with constant parameters. The substructure analysis of such a model, augmented with a set of \"hidden\" flow variables, readily highlights an inevitability of the frequency-dependence found in the measured flow forces, when these are condensed at the measurement degrees of freedom. The formulation thus obtained clearly suggests the mathematical structure of the measured fluidelastic forces, in particular providing the formal justification for a modelling approach often used in unsteady aeroelasticity. Then, inspired by previous work in the fields of viscoelasticity and soil-structure interaction, we proceed by identifying adequate frequency-independent second-order flow-coupling matrices from the frequency-dependent experimental data, which is a challenging identification problem, even for the specific case of symmetric coupling detailed here. Finally, the developed concepts and procedures are applied to experimental results obtained at CEA-Saclay (France), for the fluidelastic interaction forces acting on a flexible tube within a rigid bundle, although the problem addressed embraces a much wider range of applications. The proposed flow modelling and identification approach shows significant potential in practical applications, with many definite advantages.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104127"},"PeriodicalIF":3.6,"publicationDate":"2024-05-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140906863","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aerodynamic performance and flow mechanism of 3D flapping wing using discrete vortex method","authors":"Rahul Kumar,&nbsp;Srikant S. Padhee,&nbsp;Devranjan Samanta","doi":"10.1016/j.jfluidstructs.2024.104128","DOIUrl":"https://doi.org/10.1016/j.jfluidstructs.2024.104128","url":null,"abstract":"<div><p>In this work, we have performed numerical simulations of the flapping motion of a rectangular wing in a three-dimensional flow field using the discrete vortex method (DVM). The DVM method is computationally more convenient because it does not require the generation of a grid for the flow field at each time step as in other conventional simulation methods. In addition to the rigid wing case, the aerodynamic characteristics of a deformable wing are also investigated. The deformable wing is studied in various configurations, such as bending, twisting, and bending-twisting coupling (BTC), to provide a comprehensive analysis of its performance. In this study, we have introduced a novel aerodynamic technique in wing twisting. Unlike traditional wing rotation about a fixed root axis, our approach involves rotating the wing about a dynamically adjusted point located at the root of the leading edge. This novel approach was found to be effective in increase in the requisite aerodynamic force. The BTC wing represents reflects a sophisticated aerodynamic approach that optimally coordinates both twisting and bending deformations of the wing, resulting in a substantial improvement in its overall aerodynamic efficiency. The investigation of all four modes involves a detailed analysis of the flow mechanisms and vortex dynamics, which play a crucial role in influencing the aerodynamic forces, namely lift and thrust. The study aims to understand how these flow patterns change under different operating conditions and how these changes impact the generation of lift and thrust. The lift, thrust, and propulsive efficiency of all four modes are compared to provide a detailed understanding of their aerodynamic characteristics. The bent wing showed minimal improvements in lift and thrust compared to the rigid wing. In contrast, the twisted wing showed greater improvements in both lift and thrust. The BTC wing proves to be the most efficient method to improve aerodynamic performance during flapping. The parametric dependence of kinematic parameters such as asymmetric ratio (downstroke speed to upstroke speed), aspect ratio and reduced frequency on the aerodynamic performance was also investigated.</p></div>","PeriodicalId":54834,"journal":{"name":"Journal of Fluids and Structures","volume":"127 ","pages":"Article 104128"},"PeriodicalIF":3.6,"publicationDate":"2024-05-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140879560","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}