Article
Mechanics
An-Kang Gao, Chris D. Cantwell, Onur Son, Spencer J. Sherwin
Summary: In this study, the three-dimensional transition and force characteristics of plunging airfoils are investigated using experimental measurements, numerical simulations, and linear stability analysis. The interaction between the leading-edge vortex (LEV), the previous-cycle LEV (pLEV), and the trailing-edge vortex (TEV) is found to be the primary factor affecting the 3-D transition and associated forces. The results show that different interaction patterns and vortex pairs have different effects on the stability and lift of the LEV, depending on the range of the chord-based Strouhal number St(c).
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Cheng-Nian Xiao, Inanc Senocak
Summary: Stationary longitudinal vortical rolls can occur in shallow slope katabatic and anabatic Prandtl slope flows when the surface buoyancy flux is sufficiently large. The self-pairing of these rolls is a unique flow structure that resembles speaker-wires. Subharmonic modes dominate over fundamental modes, leading to the relative stability of a single vortex pair compared to multiple pairs.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Negar Hosseini, Martin D. Griffith, Justin S. Leontini
Summary: The study shows that when the pitch between two upstream cylinders is large, the downstream wake exhibits a two-row vortex structure, and the shape of the third body has minimal impact on this structure. However, in certain cases, the position of the third body can disrupt the original vortex structure and globally broadcast its presence.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ashwini Karmarkar, Jacqueline O'Connor
Summary: The study aims to analyze how increasing free-stream turbulence affects the flow response to longitudinal acoustic excitation. By studying the flow in the wake of a cylindrical bluff body under non-reacting and reacting conditions, we find that varying the level of free-stream turbulence can influence both the amplitude and symmetry of vortex shedding in the presence of longitudinal acoustic excitation.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Daniel Fuster, Maurice Rossi
Summary: The work focuses on the basic interactions between a vortex and an interface separating two incompressible fluids. It investigates how vorticity produced at an interface influences the dynamics of the interface and engenders small scales and small droplets. The study identifies critical Weber numbers that affect the rolling up of the interface around the vortex and trigger instabilities leading to the appearance of extremely small structures.
INTERNATIONAL JOURNAL OF MULTIPHASE FLOW
(2021)
Article
Mechanics
Yunxing Su, Monica M. Wilhelmus, Roberto Zenit
Summary: Vortex rings are crucial for generating thrust underwater. This study investigates the evolution of isolated vortex rings crossing a stable two-layer system and examines how their translation direction relative to gravity affects their behavior. The production of baroclinic vorticity is found to significantly impact the propagation of vortex rings at the density interface. The results highlight the breakdown of symmetry between vortex rings traveling from dense to light fluids and from light to dense fluids, with the maximum penetration depth occurring when the vortex propagates against the density gradient.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
Xinran Zhao, Carlo Scalo
Summary: In this study, the conservation of total helicity through viscous reconnection events in topologically complex vortex flows was investigated using direct numerical simulations. The results demonstrated a clear correlation between helicity annihilation and viscous circulation transfer processes, revealing fundamental hydrodynamic mechanisms responsible for the production/destruction of total helicity during reconnection events.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Bartosz Protas, Stefan G. Llewellyn Smith, Takashi Sakajo
Summary: In this study, the rotating and translating equilibria of open finite vortex sheets in two-dimensional potential flows were considered, and new results were obtained regarding their stability. The linear instability of these equilibria was shown, with different growth characteristics of unstable perturbations in time. Interestingly, the stability results were obtained entirely through analytical computations, and comparisons were made with existing results for unbounded, periodic, and circular vortex sheets.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
A. Castillo-Castellanos, S. Le Dizes
Summary: This study investigates the base flow in the far wake of a rotor, based on the research by Castillo-Castellanos et al. in 2021. The long-wave stability of these solutions is analyzed using a vortex filament framework, revealing different types of instability modes.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Ching Chang, Stefan G. Llewellyn Smith
Summary: This study extended the analysis of the curvature instability of thin vortex rings with different densities inside and outside the vortex core in the presence of surface tension, finding that the vortex rings are unstable to resonant waves in the presence of density variations and surface tension. The main modes are enhanced by density variations in the small axial wavenumber regime, while the effect of surface tension is marginal. The growth rates of non-principal modes were also examined, with long waves being the most unstable.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Ching Chang, Stefan G. Llewellyn Smith
Summary: The Moore-Saffman-Tsai-Widnall (MSTW) instability is a parametric instability that arises in strained vortex columns. Results show that the stationary resonant waves are more unstable when the density ratio approaches zero, and the growth rate is maximised near resonance. Surface tension suppresses the instability, with its effect being less significant than that of density. As the azimuthal wavenumber increases, the MSTW instability decays.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Suresh Behara, Venu Chandra, N. R. Prashanth
Summary: This study numerically investigates the three-dimensional transition in the wake of two tandem co-rotating cylinders. The results show that the rotation of the cylinders and the change of the streamwise gaps both affect the transition modes and the characteristics of the near-wake flow.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Xiao Zhang, Joseph D. Chung, Elaine S. Oran
Summary: Recent work has investigated the blue whirl, a soot-free hydrocarbon flame, and found that it is composed of a triple flame in a swirling flow undergoing vortex breakdown. This paper presents three-dimensional numerical simulations of triple flames in swirling flows with and without vortex breakdown, and discusses their relation to the blue whirl. The results show that the shape of the triple flame depends on the occurrence and location of vortex breakdown. The findings provide insights into the flow structure and flame shapes of the blue whirl.
COMBUSTION AND FLAME
(2022)
Article
Mechanics
Hongyi Jiang
Summary: This study identifies and explains the formation mechanisms of secondary vortex street in the far wake of a circular cylinder for different Reynolds numbers. It demonstrates that both hydrodynamic instability of the mean flow and merging of layered vortices play a role in the formation, with their dominance depending on the Reynolds number. The variation in streamwise locations for the emergence of secondary vortices with Reynolds number is quantified and explained.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Hongyi Jiang
Summary: The study investigates the three-dimensional wake transition for flow past a diamond cylinder at different Reynolds numbers, revealing variations in wake characteristics such as mode swapping between modes A and B, as well as the gradual disorganization of mode B. It is found that there are major differences in wake properties between a diamond and a circular cylinder, with the decomposition of flow properties aiding in the understanding of these differences. The complex interactions between streamwise and spanwise vortices, as well as the wake transition and base-flow transition, are identified as factors that excite mode B and suppress the subharmonic mode.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Mechanical
A. Rao, M. C. Thompson, T. Leweke, K. Hourigan
JOURNAL OF FLUIDS AND STRUCTURES
(2015)
Review
Mechanics
Thomas Leweke, Stephane Le Dizes, Charles H. K. Williamson
ANNUAL REVIEW OF FLUID MECHANICS, VOL 48
(2016)
Article
Engineering, Aerospace
Antoine Joulain, Damien Desvigne, David Alfano, Thomas Leweke
JOURNAL OF AIRCRAFT
(2017)
Article
Mechanics
H. Bolnot, S. Le Dizes, T. Leweke
FLUID DYNAMICS RESEARCH
(2014)
Article
Mechanics
L. Mununga, D. Lo Jacono, J. N. Sorensen, T. Leweke, M. C. Thompson, K. Hourigan
JOURNAL OF FLUID MECHANICS
(2014)
Article
Mechanics
M. Brons, M. C. Thompson, T. Leweke, K. Hourigan
JOURNAL OF FLUID MECHANICS
(2014)
Article
Mechanics
Hugo Umberto Quaranta, Mattias Brynjell-Rahkola, Thomas Leweke, Dan S. Henningson
JOURNAL OF FLUID MECHANICS
(2019)
Article
Mechanics
F. Y. Houdroge, T. Leweke, K. Hourigan, M. C. Thompson
JOURNAL OF FLUID MECHANICS
(2020)
Article
Mechanics
F. Y. Houdroge, J. Zhao, S. J. Terrington, T. Leweke, K. Hourigan, M. C. Thompson
Summary: This comprehensive investigation explores the motion and forces on spheres of different density ratios rolling down an incline in a fluid under gravity. Experimental, computational, and analytic methods are used, revealing the influence of Reynolds number, mass ratio, and surface roughness on the flow behavior. The study also highlights the transition to chaotic wake flow at lower Reynolds numbers and the presence of flow-induced vibrations.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
F. Y. Houdroge, T. Leweke, K. Hourigan, M. C. Thompson
JOURNAL OF FLUID MECHANICS
(2017)
Proceedings Paper
Mechanics
Farah Yasmina Houdroge, Mark C. Thompson, Thomas Leweke, Kerry Hourigan
ADVANCES IN FLUID-STRUCTURE INTERACTION
(2016)
Proceedings Paper
Energy & Fuels
S. Ivanell, T. Leweke, S. Sarmast, H. U. Quaranta, R. F. Mikkelsen, J. N. Sorensen
WAKE CONFERENCE 2015
(2015)
Proceedings Paper
Energy & Fuels
Hadrien Bolnot, Stephane Le Dizes, Thomas Leweke
WIND ENERGY - IMPACT OF TURBULENCE
(2014)
Proceedings Paper
Energy & Fuels
T. Leweke, H. U. Quaranta, H. Bolnot, F. J. Blanco-Rodriguez, S. Le Dizes
SCIENCE OF MAKING TORQUE FROM WIND 2014 (TORQUE 2014)
(2014)