Fluid Dynamics最新文献

{"title":"Geometric Consistency in Taylor Analogy Modeling of Droplet Deformation in the Small Deformation Regime","authors":"M. H. Bui,&nbsp;T. T. Nguyen","doi":"10.1134/S0015462826605437","DOIUrl":"10.1134/S0015462826605437","url":null,"abstract":"<p>Taylor analogy deformation models are widely used to predict droplet deformation in planar extensional flows, where model performance is commonly evaluated using the Taylor deformation parameter. However, the agreement in the Taylor deformation parameter alone does not necessarily ensure accurate prediction of droplet geometry, because the droplet elongation and size are fundamentally governed by the droplet interface displacement. As a result, relying solely on the Taylor deformation parameter may conceal errors in droplet elongation, even when the apparent deformation is reasonably reproduced. In addition, the existing models show limited predictive capability at low viscosity ratios. In the present study, the geometric consistency of Taylor analogy modeling is examined in the small deformation regime using three-dimensional numerical simulations. The results show that the limitations of existing models originate from simplified geometric assumptions used to relate the droplet interface displacement to the Taylor deformation parameter. Based on these findings, a geometry-consistent formulation is proposed to improve the prediction of both droplet elongation and deformation across a wide range of viscosity ratios, including the low viscosity ratio regime.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aspect Ratio and Drag Coefficient of Coalescing Bubbles in a Narrow Channel with Bottom Gas Injection","authors":"C. Tang,&nbsp;R. Dong,&nbsp;H. Zou,&nbsp;X. Zhang,&nbsp;R. Chen","doi":"10.1134/S0015462826605097","DOIUrl":"10.1134/S0015462826605097","url":null,"abstract":"<p>The drag coefficient and bubble morphology are essential in influencing the adjacent flow field and the properties of heat and mass transfer. Nonetheless, precisely forecasting these parameters for numerous bubbles or bubble clusters continues to be a significant challenge. This study systematically investigates the impact of varying gas flow rates and NaCl solution concentrations on the bubble aspect ratio and the drag coefficient. Employing high-speed videography alongside sophisticated image processing methods, therefore, the equivalent bubble diameter, the ascent velocity, and the aspect ratio of bubbles produced in restricted vertical channels are accurately quantified. The principal findings indicate that the aspect ratio converges to approximately 0.35 as the bubble diameter increases. In dilute NaCl solutions, the aspect ratio exhibited greater variability as the gas flow rate increased from 50 to 300 mL/min. A strong correlation, with a coefficient of determination of 0.915, is shown between the experimental aspect ratios and predictions based on the Weber and Eötvös numbers. Moreover, the pace of bubble ascent escalates with both the solution concentration and the equivalent bubble diameter. The drag coefficient decreases as the Reynolds number increases. A novel empirical correlation, integrating bubble deformation and the Reynolds number, is introduced to forecast the drag coefficient with a maximum relative error of 16.5%. These discoveries offer essential insights into dynamics of gas–liquid two-phase heat and mass transport.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034963","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Numerical Investigation of Particle Chain Settling in a Channel for Non-Newtonian Fluids Using the Fictitious Domain Method","authors":"I. Abbas,&nbsp;K. Usman","doi":"10.1134/S0015462826604729","DOIUrl":"10.1134/S0015462826604729","url":null,"abstract":"<p>Particulate flows are important in the delivery of drugs, the sedimentation of rivers, and the management of concrete. The rheological properties of fluids have a significant influence on the settling behavior of particles in these flows. The behavior of particles in flowing and sedimenting systems of chained aggregates, particularly in the context of shear-thinning, shear-thickening, and yield stress fluid rheology, is still insufficiently understood. The present study seeks to determine the effects of the rheological properties of a power-law fluid on dynamics of chain-structured circular particles in a fluid of rheological indices <i>n</i> = 0.9, <span>(n = 1.0,)</span> and <span>(1.1)</span>. A computational approach is used to study the interaction of particles with an incompressible fluid system using the Eulerian technique and the fictitious domain method (FDM). The direct volume integral method is used to compute the hydrodynamic forces of the system with a collision model for particle-particle interactions. The open-source FEATFLOW application utilizes the multigrid finite element method to structure the spatial domain, offering flexibility in simulating both fluid and particle configurations. The study illustrates how the power-law index provides varying dominant particle dynamics in various configurations of the system.</p><p>For instance, shear-thinning fluids <span>(left( {n = 0.9} right))</span> provide flexible control of the particles, while shear-thickening fluids <span>(left( {n = 1.1} right))</span> impose rigid control of the particles. The rheological properties greatly influence chain formations of settling particles. Shear-thinning fluids enhance the rapid sedimentation of particles, while shear-thickening fluids induce slower and more stable configurations during sedimentation. The collision times and particle displacement were observed to vary with fluid rheology, with shear-thickening fluids demonstrating increased interparticle interactions and less particle displacement.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nonlinear Sloshing Waves between Two Immiscible Electrified Liquids in an Oscillating Rectangular Container","authors":"M. A. Sirwah,&nbsp;K. Zakaria,&nbsp;S. Nour Eldeen,&nbsp;K. M. Elmorabie","doi":"10.1134/S0015462826604870","DOIUrl":"10.1134/S0015462826604870","url":null,"abstract":"<p>The sloshing response of a liquid layer in a rigid rectangular container subjected to a vertical excitation is investigated taking into accounts the effect of both interfacial tension and electrical voltage difference between the vertical container walls. The discussion is dealing with demonstrating the structure of resonated three modes of surface waves on the liquid free interface. The non-dimensional mathematical equations governing the problem together with the associated boundary conditions are formulated up to the second order of nonlinearity. The evolution equations of the resonated waves are derived, then the method of multiple time scales is utilized to construct a third order dynamical system governing the amplitudes of the resonated waves including the second interaction terms. Such a system, in which the effects of several model parameters on the dynamical properties of flow pattern are studied, is solved numerically. The numerical computations revealed that the electric voltage difference applied to the container’ side walls as well as the electric permittivities of the two fluids plays a significant role in damping the interfacial waves and trend to stabilize the liquid motion, whereas the amplitudes of the external excitation that the container exposed trends to enhances the instability of flow motion where they tend to disrupt fluid movement, increase the pressure on the container body, and pose a significant risk to the integrity of the container.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034638","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"CFD-Based Investigation of the Drag-Reduction Characteristics in Heterogeneous Autonomous Underwater Vehicle Formations","authors":"Q. Gao,&nbsp;H. L. Xu,&nbsp;Y. Y. Luo","doi":"10.1134/S0015462826605942","DOIUrl":"10.1134/S0015462826605942","url":null,"abstract":"<p>To investigate the hydrodynamic interaction and drag-reduction potential of heterogeneous autonomous underwater vehicle (AUV) formations during formation cruising, this study performs a computational fluid dynamics (CFD)-based analysis of a three-AUV heterogeneous formation consisting of one DARPA SUBOFF model and two Zebrafish 150 AUVs. The Reynolds-averaged Navier–Stokes (RANS) equations coupled with the <i>k</i>–ω shear stress transport (SST) turbulence model are employed to conduct numerical simulations and comparative analyses of the resistance characteristics and the pressure-field distributions for four representative configurations: tandem, triangular, parallel, and inverted triangular formations, under various inter-vehicle spacings. The numerical method is first validated against resistance test data of the SUBOFF model. The results show that the CFD prediction errors at the medium and high speeds are within 5%. That satisfies the requirements for relative hydrodynamic comparison among formation configurations in this study. On this basis, the individual drag variation ratio and the overall formation drag variation ratio are introduced to evaluate the drag-reduction performance of various formations. The results indicate that the drag-reduction capability of heterogeneous AUV formations is not determined simply by reduced inter-vehicle spacing, but is primarily governed by wake continuity, wake coverage, and lateral pressure coupling. The tandem formation forms a continuous multi-stage wake-shielding structure, with an overall formation drag variation ratio <i>C</i>_form of approximately from  –10 to –13%, making it the most effective drag-reduction configuration among the investigated cases. The triangular formation exhibits coexistence of local wake utilization and lateral interference, and its overall drag-reduction effect is not significant. The parallel formation is mainly affected by lateral pressure coupling and gap-acceleration effects, which can easily lead to an increase in the overall resistance. The inverted triangular formation can provide local drag reduction for the large AUV at specific spacings, but this benefit is offset by the increased resistance of the two small AUVs, with the optimum overall drag variation ratio being –1.563%. The findings provide a reference for drag-reducing cruising-formation design and mission formation control of heterogeneous AUV swarms.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034625","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Starting a Convergent–Divergent Nozzle with a Busemann Diffuser","authors":"Yu. V. Tunik","doi":"10.1134/S0015462826606170","DOIUrl":"10.1134/S0015462826606170","url":null,"abstract":"<p>The problem of starting a convergent–divergent nozzle with a Busemann diffuser that provides a given air heating is solved. The starting simulates the nozzle acceleration in still air to a certain supersonic Mach number. The influence of viscosity on the diffuser flow is numerically investigated. The modeling is performed based on the two-dimensional non-stationary Navier−Stokes equations and the Godunov−Kolgan finite-difference scheme, adapted for calculating axisymmetric viscous gas flows. It is shown that starting the nozzle does not make it possible to obtain steady-state isentropic flow in form of a centered compression wave in the Busemann diffuser. The growth of the viscous layer leads to the formation of a system of inclined and normal shock waves moving upstream and creating zones of subsonic flow in the diffuser. The approach to the Busemann solution is not guaranteed to be reached even in the case of inviscid gas.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mechanism Analysis of the Effect of Medium Molecular Weight on Monatomic Jet-Induced Transition Promotion on Compression Surfaces","authors":"W. Y. Zeng,&nbsp;Y. Xu,&nbsp;Z. He,&nbsp;J. L. Le,&nbsp;X. Z. Xia,&nbsp;H. X. Wang,&nbsp;R. L. Zhang","doi":"10.1134/S0015462826605383","DOIUrl":"10.1134/S0015462826605383","url":null,"abstract":"<p>To enhance the resistance of the compression surface boundary layer to adverse pressure gradients and mitigate the risk of non-start in air-breathing engines, promoting an early transition to turbulence is crucial. This study investigates the use of wall-injected jets to trigger boundary layer transition on inlet compression surfaces, proposing a novel analytical framework that incorporates jet shear layer development analysis. The methodology involves establishing grid independence using the γ_θ–Re_θ transition model and validating numerical simulations against wind tunnel data. Key flow parameters, including the streamwise velocity and the density, were extracted from the near-wall region downstream of micro-jets injecting monatomic gases of varying molecular weights. Analysis of the evolving jet shear layers revealed how the molecular weight of the jet injectant influences the transition process and the wall heat flux. By examining the underlying mechanisms through the shear layer flow characteristics and vorticity theory, it was determined that higher molecular weights intensify the development of the jet shear layer and associated flow perturbations. These enhanced disturbances accelerate the boundary layer transition, leading to increased skin friction and wall heat flux. Compared to helium (the lightest gas), krypton (the heaviest) shifted the transition onset and completion locations upstream by up to 32.8 and 55.7%, respectively. Despite the transition promotion, the jets reduced wall skin friction relative to the no-jet case by diminishing the Reynolds stress and the wall-normal gradient of streamwise velocity, thereby partially counteracting the associated increase in heat flux. These findings provide valuable theoretical support for advancing active flow control strategies based on jet-induced transition.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Visualization Study of the Effects of Fuel Viscosity and Surface Tension on Cavitation Flow in Full-Scale Transparent Nozzles","authors":"J. C. Gu,&nbsp;Z. H. Feng,&nbsp;X. Yang,&nbsp;L. L. Tang,&nbsp;X. Q. Tian,&nbsp;Z. H. He","doi":"10.1134/S0015462826605486","DOIUrl":"10.1134/S0015462826605486","url":null,"abstract":"<p>The pursuit of cleaner combustion in engines has positioned alternative fuels as a critical enabler, yet their diverse range of viscosities and surface tensions poses a fundamental challenge to the regulation of nozzle internal flow behavior. In this study, full-scale transparent nozzles and high-speed microscopic imaging are employed to directly visualize the fuel internal flow. Additionally, glycerol–AES (sodium fatty alcohol ether sulfate)–aqueous solutions are formulated to decouple the effects of viscosity and surface tension, enabling a quantitative and independent investigation of their impact on cavitation flow. The results show that cavitation inside the nozzle undergoes clear temporal evolution during injection. Three distinct cavitation regimes were observed and defined, which are geometry-induced cavitation, needle-originated string cavitation, and hole-sac string cavitation. Their evolution is governed by the coupled effect of flow separation, vortex dynamics, and nozzle geometry. Surface tension is shown to have a negligible influence on string cavitation, in contrast, fuel viscosity plays a critical and non-monotonic role by modulating vortex evolution. Higher viscosity delays the inception of string cavitation while enhancing its stability and duration. Another key finding is that the relative position between the nozzle hole inlet and the conical surface of the needle valve tip significantly affect the initial position and reflux zone position of the fuel flow and separation in the sac, thereby determining whether increased viscosity enhances or suppresses the cavitation intensity. This study provides the experimental basis and the theoretical guidance for application of alternative fuels and design and optimization of nozzle structures.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149034694","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Possibilities of Simplified Numerical Modeling of the Stardust Sample Descent Capsule Flight","authors":"V. Batygina","doi":"10.1134/S0015462826605425","DOIUrl":"10.1134/S0015462826605425","url":null,"abstract":"<p>The flight of the Stardust descent capsule is examined. The possibility of simplified calculation of the capsule flow is studied using the perfect gas model when varying the specific heat ratio in the NERAT-2D software. This assumption makes it possible to quickly obtain the accurate flow pattern over a certain altitude range, but often it underestimates the heat flux to the capsule surface.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148903522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Study of the Unmanned Aerial Vehicle Propeller Performances Near Ceiling: Experimental, Numerical and CFD-based Approaches","authors":"S. C. De Silva,&nbsp;M. Phlernjai","doi":"10.1134/S001546282660505X","DOIUrl":"10.1134/S001546282660505X","url":null,"abstract":"<p>The ceiling effect is a significant factor for unmanned aerial vehicle (UAV) missions that require close flight in the proximity of top planar boundaries such as inverted docking, perching, and flight in a confined space. In this study, the ceiling effect on a 5.5-inch propeller of a small UAV and a 9-inch of a medium-sized UAV was modeled and simulated using computational fluid dynamics (CFD) with multiple reference frame (MRF) method. The result was then validated by an experimental method at propeller speeds ranging from 5000 to 9000 RPM. For the near-ceiling region, computational fluid dynamics and experiment setup results for the propeller thrust were compared with the Cheeseman and Bennett model, the Hayden model, and also using the Conyers model. The results showed a close agreement between the computational fluid dynamics and experimental results, as well to the theoretical models, with some errors. Further, the validated CFD results were used to investigate the extreme-near ceiling region, which is not currently covered by the theoretical models. Our contribution in this study wishes to provide more understanding of such effects in the extreme near ceiling on a single-rotor model by using the velocity streamlines, thus possibly expand to multi-rotor unmanned aerial vehicles (UAVs) of different sizes in future research.</p>","PeriodicalId":560,"journal":{"name":"Fluid Dynamics","volume":"61 5","pages":""},"PeriodicalIF":0.7,"publicationDate":"2026-09-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"148903523","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}