Article
Mechanics
J. Sierra-Ausin, M. Lorite-Diez, J. I. Jimenez-Gonzalez, V. Citro, D. Fabre
Summary: This study examines the spatio-temporal pattern formation of wake flow past a streamwise rotating sphere from a dynamical system perspective. It reveals the connection between rotating waves and helical patterns within the wake. The research finds that, for low rotation rates, the flow field undergoes a transition similar to that of flow past a static sphere, but with a rapid variation in flow frequencies due to rotation. The transition from a single helix pattern to a double helix structure within the wake displays hysteric behavior in several regions. Eventually, the interaction between single and double helix structures leads to temporal chaos.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Kai-Xin Hu, Sheng Zheng, Qi-Sheng Chen
Summary: The external excitations in thermocapillary liquid layers are investigated through non-modal stability theory, with amplification depending on perturbation velocity and temperature. Large amplifications can occur in subcritical flows at both small and large Prandtl numbers, but the response properties differ significantly between small and large Pr. An optimal response is achieved when the perturbation is nearly a spanwise wave, and the amplification mechanisms also vary between small and large Pr.
Article
Mechanics
Yuping Bai, Peiwen Yan, Quanbin Zhao, Daotong Chong, Yifei Yu, Zhihui Zhang, Junjie Yan
Summary: The origin and relationship between initial streamwise vortices in braid regions and deformed spanwise vortices are studied using direct numerical simulation (DNS) in a compressible mixing layer. Through analysis of DNS data using fast Fourier transform, two low-rank velocity models (v(d) and v(s)) are developed to show that both deformed spanwise vortices and streamwise vortices originate from the linear superposition of several modes. Further investigations reveal that the increase in amplitude ratio between modes leads to the formation of deformed spanwise vortices in vortex regions and the generation of streamwise vortices in braid regions.
Article
Mechanics
S. F. Lewin, C. P. Caulfield
Summary: Motivated by the variation of local shear produced by internal waves in the ocean, this study investigates the effect of a time-dependent shear forcing on the evolution and mixing of turbulence produced by Kelvin-Helmholtz instability (KHI) through direct numerical simulations. The results demonstrate that turbulence produced by KHI with a decelerating shear mixes in a distinctly different way from the flow with constant background shear, with characteristics more in common with convectively driven flows.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Alexander Nepomnyashchy, Ilya Simanovskii
Summary: This study investigates the effect of vibration on Marangoni flows in a droplet on a liquid substrate. Numerical analysis using longwave amplitude equations shows that vibration can change the shape of the droplet, resulting in rhombic droplets. The shape of the droplet significantly influences its oscillations.
Article
Astronomy & Astrophysics
Jean-Francois Clouet, Olivier Soulard
Summary: This paper investigates the exchange of momentum between photons and material particles in a turbulent stellar flow, analyzing the radiative viscous stress and return-to-the-mean form of radiative force in different optical regimes. The results show that the radiative force dissipates kinetic energy, with an upper bound on dissipation in optically thin situations, and these findings hold true for frequency-dependent opacities.
ASTROPHYSICAL JOURNAL
(2021)
Article
Mechanics
Zhaobin Li, Guodan Dong, Xiaolei Yang
Summary: In this work, the effects of the side-to-side motion of a floating offshore wind turbine (FOWT) on wake dynamics were investigated. It was found that the motion frequency overlapping with the wake meandering frequency induced by the shear layer instability can lead to wake meandering with larger amplitudes. The onset of wake meandering is dominated by the inflow turbulence for high turbulence intensity. The probability density function of the spanwise instantaneous wake centers is non-Gaussian and closely related to the side-to-side motion. Linear stability analysis can accurately predict the least stable frequencies and the amplification factor for a certain motion amplitude, and nonlinearity affects the results when the motion amplitude increases.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Thermodynamics
Shatrughan Prasad Jaiswal, Madhusudhana Gavara
Summary: The study focuses on the Rayleigh-Taylor instability in viscosity varying fluid layers. The configuration becomes more unstable when the viscosity of the fluid layers varies with temperature, and the spike undergoes large deformations. The instability is affected by the viscosity ratio, temperature ratio, heating location, Prandtl number, and Weber number, with increasing viscosity ratio showing a stabilizing effect and increasing temperature ratio showing a destabilizing effect. The top wall heating configuration leads to earlier formation of mushroom shaped spike and skirt compared to the bottom wall heating configuration. The Prandtl number has an insignificant effect on the instability.
INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER
(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
Anna E. Samoilova, Alexander Nepomnyashchy
Summary: This study investigates pattern formation in a thin film heated from below due to oscillatory Marangoni instability, focusing on the stability of patterns produced by nonlinear interaction of two standing waves propagating at an angle phi between wave vectors. Weakly nonlinear analysis within amplitude equations revealed stable traveling rectangles and alternating rolls on a rhombic lattice, with coefficients of Landau equations defining pattern formation calculated across a wide range of governing parameters.
Article
Mechanics
Chuhan Wang, Lutz Lesshafft, Kilian Oberleithner
Summary: This study investigates the linear stability of a laminar premixed flame anchored on a square cylinder and confined inside a channel. The results show that linear instability analysis accurately predicts critical flow parameters for the onset of limit-cycle oscillations and indicates a stabilizing effect of flame ignition. The study also finds that instability in ignited wake flows occurs at high Reynolds numbers and is driven by hydrodynamic mechanisms similar to non-reacting wake flows. Linear eigenmode analysis can accurately retrieve the frequency of nonlinear limit-cycle flame oscillations if the full set of reacting flow equations is linearized.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Yajun Fan, Vladimir Parezanovic, Olivier Cadot
Summary: The paper experimentally investigates the sensitivity of aerodynamic force and body pressure distribution when the flow passes a flat-back, taller than wide Ahmed body in the context of ground vehicle aerodynamics. The study reveals significant non-trivial transitions and sharp base pressure gradients in the parameter spaces, which have important implications for the vehicle's performance. Furthermore, the steady near wake z-instability can be suppressed by using a rear cavity.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
G. Nastro, J. -C. Robinet, J. -C. Loiseau, P. -Y. Passaggia, N. Mazellier
Summary: In this study, the stability and sensitivity of two-and three-dimensional global modes developing on steady spanwise-homogeneous laminar separated flows around NACA 4412 swept wings were numerically investigated. It was found that the introduction of a sweep angle attenuates the growth of all unstable modes and entails a Doppler effect in the leading modes' dynamics. The sensitivity analysis revealed that a streamwise-oriented force on the suction side of the wing has a stabilizing effect, and a spanwise-homogeneous force can suppress the Hopf bifurcation and stabilize the entire branch of von Karman modes.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Mechanics
D. Bansal, D. Ghosh, S. Sircar
Summary: This study provides a detailed comparison of the linearized analyses of viscoelastic free shear flows under different constitutive equations, showing stability characteristics such as elastic stabilization at higher elasticity numbers and nonmonotonic instability patterns at low to intermediate values of elasticity number for the JS and PTT models. The impact of elasticity, Reynolds number, and viscosity on temporal stability curves of the PTT model is explored, revealing the effects of centerline shear rate on the behavior transition between JS and PTT models. The phase diagrams illustrate regions of inertial turbulence modified by elasticity, elastic turbulence, elastoinertial turbulence, and a stable region for intermediate values of Reynolds and elasticity number.
Article
Mechanics
V. V. Konovalov, D. Lyubimov, T. P. Lyubimova
Summary: The study focuses on resonance oscillations of a single liquid drop or gas bubble relative to their equilibrium spherical shape, investigating the effect of viscosity on resonance and revealing the equivalence of two methods in accounting for viscosity.
Article
Engineering, Multidisciplinary
Thomas Boeck, Dzulia Terzijska, Gabriele Eichfelder
JOURNAL OF ENGINEERING MATHEMATICS
(2018)
Article
Engineering, Multidisciplinary
Daniel Hernandez, Thomas Boeck, Christian Karcher, Thomas Wondrak
MEASUREMENT SCIENCE AND TECHNOLOGY
(2018)
Article
Mechanics
Sebastian Prinz, Thomas Boeck, Joerg Schumacher
EUROPEAN JOURNAL OF MECHANICS B-FLUIDS
(2018)
Article
Physics, Fluids & Plasmas
Vinodh Bandaru, Thomas Boeck, Joerg Schumacher
PHYSICAL REVIEW FLUIDS
(2018)
Article
Mechanics
Oleg Zikanov, Dmitry Krasnov, Thomas Boeck, Semion Sukoriansky
JOURNAL OF FLUID MECHANICS
(2019)
Article
Mechanics
D. Krasnov, Y. Kolesnikov, T. Boeck
Article
Thermodynamics
Sebastian Prinz, Joerg Schumacher, Thomas Boeck
INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW
(2019)
Article
Engineering, Multidisciplinary
Sebastian Prinz, Jana Thomann, Gabriele Eichfelder, Thomas Boeck, Joerg Schumacher
Summary: This paper introduces a novel trust-region method for optimizing multiple expensive functions, applied to a biobjective optimization problem in fluid mechanics. By using interpolation models and trust regions, computational time is minimized in finding descent directions.
OPTIMIZATION AND ENGINEERING
(2021)
Article
Engineering, Mechanical
Thomas Boeck, Seyed Loghman Sanjari, Tatiana Becker
NONLINEAR DYNAMICS
(2020)
Article
Engineering, Mechanical
Ze Lyu, Thomas Boeck, Christian Karcher
Summary: Experimental results show that the force sensor can detect a moving particle in a quiescent conducting liquid. The structure of the Fx signal can be reproduced with less variation and is less sensitive to the Reynolds number than the Fz signal. Furthermore, the structure and magnitude of time-dependent Lorentz force signals can be reasonably predicted by a numerical model.
EXPERIMENTS IN FLUIDS
(2021)
Article
Engineering, Mechanical
Thomas Boeck, Seyed Loghman Sanjari, Tatiana Becker
Summary: The article studies the behavior of vertically driven pendulum with additional electromagnetic interaction caused by eddy currents in a nearby thick conducting plate. The motion equation of the pendulum is derived and the conditions for equilibrium instability are obtained. Numerical analysis shows that strong electromagnetic interaction leads to significant differences between analytical and numerical results, and the area of harmonic instability can become doubly connected. Chaotic motions can also occur under moderately strong driving.
NONLINEAR DYNAMICS
(2022)
Article
Mechanics
Shashwat Bhattacharya, Thomas Boeck, Dmitry Krasnov, Joerg Schumacher
Summary: We investigate how fringing magnetic fields affect turbulent thermal convection in a horizontally extended rectangular domain. By controlling the gap between the magnetic poles and the convection cell, we vary the fringe width and observe the changes in large-scale structures and heat transport. We find that as the local vertical magnetic field strength increases, the structures become thinner and align perpendicular to the sidewalls.
JOURNAL OF FLUID MECHANICS
(2023)
Proceedings Paper
Engineering, Mechanical
Oleg Zikanov, Dmitry Krasnov, Thomas Boeck, Semion Sukoriansky
PROCEEDINGE OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019, VOL 1
(2019)
Proceedings Paper
Engineering, Electrical & Electronic
Ch. Karcher, Z. Lyu, Th. Boeck, N. Tran, U. Luedtke
9TH INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC PROCESSING OF MATERIALS (EPM2018)
(2018)
Proceedings Paper
Engineering, Electrical & Electronic
Z. Lyu, Ch. Karcher, Y. Kolesnikov, Th. Boeck
9TH INTERNATIONAL SYMPOSIUM ON ELECTROMAGNETIC PROCESSING OF MATERIALS (EPM2018)
(2018)