Article
Engineering, Marine
Jian Li, Peng Wang, Xiaoyi An, Da Lyu, Ruixuan He, Baoshou Zhang
Summary: This paper investigates the performance of flapping foils, showing that oncoming vortices facilitate the flapping motion while increasing heaving amplitude can lead to a decrease in propelling efficiency. Additionally, using a symmetric NACA0050 foil type and increasing thickness can result in higher efficiency. The research introduces a new parameter, the energy transforming ratio (R-ET), to explain the energy transforming procedure of the flapping foil.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(2021)
Article
Mechanics
Jianxun Zhu, Fengjian Jiang, Lars Erik Holmedal
Summary: The study investigates the three-dimensional flow past an elliptic cylinder with an aspect ratio of 0.5 near a moving bottom wall, analyzing the transition between two- and three-dimensional flow regimes for different gap ratios. The flow behavior shows a progression from two-dimensional to three-dimensional with various instabilities and vorticity patterns depending on the gap ratio and Reynolds number.
Article
Engineering, Marine
Sartaj Tanweer, Anupam Dewan, Sanjeev Sanghi
Summary: The study examined the three-dimensional wake transitions for a rectangular cylinder at different gap ratios and aspect ratios, finding that changes in flow rate near the cylinder and shear-layer interactions are the causes of wake transitions.
Article
Engineering, Marine
Jian Li, Xinjing Wang, Xiaoyi An, Baoshou Zhang, Da Lyu, Peng Wang
Summary: The interaction between a flapping foil and the oncoming von Karman wake significantly affects the hydrodynamic performance of the foil, and it can be utilized as an energy harvester. The highest propulsive efficiency and energy harvesting efficiency values are 50.33% and 20% respectively, and can be calculated using the energy transformation ratio (RET).
Article
Engineering, Marine
Quang Duy Nguyen, Chengwang Lei
Summary: This study investigates the hydrodynamics of a circular cylinder in confined flows, revealing significant increases in drag coefficient and Strouhal number due to confinement. The behavior of the lift coefficient varies in laminar and turbulent flow regimes. Additionally, a reverse Karman vortex street is observed at lower Reynolds numbers with specific arrangements.
Article
Physics, Multidisciplinary
Zhong-Hong Xi, Yong-Zhen Zhao, Yu-Ren Shi
Summary: This study investigates the Benard-von Karman vortex street in dipolar Bose-Einstein Condensate trapped by a harmonic potential using numerical simulations. It is found that under specific conditions, vortex pairs released from a moving obstacle potential in dipolar BEC can form a Benard-von Karman vortex street. The research also examines the effects of dipole interaction strength, obstacle potential width, and velocity on the vortex structure produced in the wake, and calculates the drag force on the obstacles potential.
PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS
(2021)
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
Sartaj Tanweer, Anupam Dewan, Sanjeev Sanghi
Summary: The study examines three-dimensional flow transitions near a square cylinder placed near a moving wall in the presence of buoyancy. The interactions between the shear-layers near the cylinder and the wall, as well as the baroclinic production of vorticity, play key roles in the onset of three-dimensionality. Different modes of varying wavelengths are formed for different values of Ri and G/D, with streamwise baroclinic vorticity strengthening three-dimensionality.
Article
Engineering, Marine
Fadong Gu, Yadong Huang, Desheng Zhang
Summary: This paper investigates the cavitation characteristics in the wake of a circular cylinder with multiscale vortices using Large Eddy Simulation (LES). It is found that cavitation can inhibit vortex shedding and induce the merging or splitting of cavities in the wake. The study provides insights into the interaction between cavitation and vortices in fluid dynamics.
JOURNAL OF MARINE SCIENCE AND ENGINEERING
(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
Thermodynamics
J. M. Perez, F. Sastre, S. Le Clainche, A. Velazquez, J. M. Vega
Summary: This paper presents a method for three-dimensional reconstruction of the velocity field in laminar flows using planar PIV data, which successfully reconstructs the streamwise velocity component with experimental data and processing tools.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2022)
Article
Mechanics
R. H. Hernandez
Summary: The objective of this work is to present a coherent detection method to determine the relationships between pressure fluctuations and wake velocity in the case of turbulent flow past a cylinder. Experimental results and pressure-velocity statistics are reported, showing the mutual influence between wall pressure and wake velocity fluctuations, as well as the correlation between large scale turbulent vortex shedding and surface pressure fluctuations.
Article
Mechanics
Junyi Mi, Xiaowei Jin, Hui Li
Summary: A network model called Cascade-Net is proposed, which combines machine learning techniques with fluid mechanics to accurately predict the spatiotemporal fluctuating velocity in the near-wall wake of a circular cylinder. The model utilizes a comprehensive dataset obtained through wind tunnel testing and applies convolutional neural networks to predict the velocity fluctuations. The results demonstrate that the Cascade-Net shows good generalization performance and accurately predicts fluctuating velocity fields and the second-order moments at various Reynolds numbers.
Article
Physics, Fluids & Plasmas
Premika S. Thasu, Subrahmanyam Duvvuri
Summary: Experimental investigation of flow oscillations in the near-wake region of a two-dimensional circular cylinder at Mach 6 reveals universal behavior in oscillation frequency and Strouhal number. Coherent oscillatory activity with a phase difference of pi radians is observed in time-resolved pressure measurements on the cylinder aft surface, similar to the low-speed counterpart of cylinder wake dynamics.
PHYSICAL REVIEW FLUIDS
(2022)
Article
Mechanics
Hongjun Zhu, Bing Xu, Quanhua Li, Yue Gao, Tongming Zhou
Summary: The study investigated the flow characteristics over a round-ended cylinder, finding that both drag and lift forces are sensitive to the incidence angle ranging from 0° to 90°. Additionally, asymmetric separation of boundary layers leads to a non-perpendicular time-mean pressure difference.
Article
Mechanics
Mathias Lemke, Vincenzo Citro, Flavio Giannetti
Summary: This paper discusses the active control of compressible flow past a bluff-body by means of external acoustic sources, successfully suppressing the transition leading to the von-Karman vortex street. The derived adjoint-based framework allows determination of acoustic sources for various bluff-body shapes, with optimal spatial position and associated temporal signal for control. The proposed methodology and results can be used to design a control strategy coupled with a continuation procedure to obtain unstable solutions beyond the critical threshold.
FLUID DYNAMICS RESEARCH
(2021)
Article
Physics, Fluids & Plasmas
Claudio Chicchiero, Antonio Segalini, Simone Camarri
Summary: The study investigates the effect of surface roughness on steady laminar flow induced by a rotating disk submerged in a fluid at rest. A theory with a triple-deck analysis is proposed to evaluate the flow modification due to rough surface at low computational cost. Numerical simulations with various roughness geometries validate the theory, showing that it quantifies flow modifications effectively.
PHYSICAL REVIEW FLUIDS
(2021)
Article
Computer Science, Interdisciplinary Applications
J. Sierra, P. Jolivet, F. Giannetti, V. Citro
Summary: In this study, an alternative methodology using the Fourier-Galerkin method is proposed for evaluating the sensitivity of periodic flows, with the stability of periodic states determined via Hill's method. The approach is applied to the Feigenbaum route to chaos in the Lorenz system and the transition to a three-dimensional state in the periodic vortex-shedding past a circular cylinder, with systematic comparisons to validate the sensitivity approach. The proposed iterative algorithm is also tested in the transition to a quasi-periodic state past two side-by-side cylinders.
JOURNAL OF COMPUTATIONAL PHYSICS
(2021)
Article
Mechanics
Pier Giuseppe Ledda, E. Boujo, S. Camarri, F. Gallaire, G. A. Zampogna
Summary: A formal framework is proposed to characterize and control/optimize the flow past permeable membranes using a homogenization approach. The study shows that the flow morphology is dominantly influenced by the filtrability of the membrane, and vortex shedding can be suppressed by employing large values of the filtrability number combined with specific slip numbers.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Mechanical
Wen-Zhen Fang, Francesco Viola, Simone Camarri, Chun Yang, Lailai Zhu
Summary: Due to an electro-hydrodynamic instability, a dielectric spherical particle can exhibit steady rotation in an electric field. Recent works have shown that using an elastic structure can generate self-oscillations through elasto-electrohydrodynamic instability. Simulations of a low-Reynolds number actuator demonstrate multiple behaviors depending on various factors, with a reduced-order model capturing the dynamics. Linear stability analysis predicts instability onset in agreement with numerical results.
NONLINEAR DYNAMICS
(2021)
Article
Mechanics
M. A. S. Al-Malki, S. J. Garrett, S. Camarri, Z. Hussain
Summary: This study investigates the effects of surface roughness on the convective stability behavior of boundary-layer flow over a rotating disk. Both anisotropic and isotropic surface roughness have different impacts on the instability properties of the flow. It was found that radial grooves have a destabilizing effect on type II mode, while concentric grooves and isotropic surface roughness stabilize the type I mode.
Article
Mechanics
Simone Camarri
Summary: In this paper, a simple strategy is proposed to connect multiple T-mixers together in order to increase flow rates. By aligning the mixers in a row and feeding them through shared inlet channels, the proposed devices exhibit engulfment flow regime for mixing. Results from numerical simulation and linear stability analysis show that this strategy can lead to compact devices with engulfment, although differences compared to isolated T-mixers may exist based on the spacing between inlet/outlet channels.
Article
Engineering, Multidisciplinary
Javier Sierra-Ausin, Vincenzo Citro, Flavio Giannetti, David Fabre
Summary: A systematic approach is proposed to analyze compressible time-periodic flows using a Fourier-Galerkin strategy. The method is free of numerical constraints and aliasing effects, and efficient algorithms are provided to solve the nonlinear problem.
COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING
(2022)
Article
Mechanics
J. Sierra-Ausin, D. Fabre, V. Citro, F. Giannetti
Summary: The mechanisms leading to acoustic whistling for a jet passing through a circular hole in a thick plate connecting two domains are investigated. Two generic situations are considered: one with a closed upstream cavity and an open downstream domain, and the other with both upstream and downstream regions considered open. A low Mach asymptotic model is used to derive a global impedance of the system, and the knowledge of this impedance provides an instability criterion and eigenvalue predictions. The method is validated against linearized fully compressible solutions and used to characterize the range of instabilities.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mathematics, Applied
I. Bochicchio, F. Giannetti, A. Sellitto
Summary: This study considers a model of nonlocal heat transfer at nanoscale in rigid bodies and analyzes three different strategies for setting up boundary conditions. The results suggest the influence of interactions on unknown fields and demonstrate the well-posedness of the problem.
ZEITSCHRIFT FUR ANGEWANDTE MATHEMATIK UND PHYSIK
(2022)
Article
Physics, Multidisciplinary
L. Leporini, V. Giannetti, M. M. Saravia, F. Califano, S. Camarri, T. Andreussi
Summary: In this study, a numerical model is used to investigate the mechanisms responsible for the breathing mode in Hall thrusters, emphasizing the importance of electron mobility fluctuations for the instability. By calibrating the model parameters against measured discharge current signals, the existence of the breathing mode is demonstrated, revealing a feedback loop involving electron mobility, neutral density, and electric field.
FRONTIERS IN PHYSICS
(2022)
Article
Mechanics
Alessandro Bongarzone, Francesco Viola, Simone Camarri, Francois Gallaire
Summary: In this study, a weakly nonlinear analysis method was used to successfully predict the impact of viscosity and static contact angle on the instability onset of viscous subharmonic standing waves under different wetting conditions. The interaction between wetting conditions and parametric waves was systematically quantified and explained.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Mechanics
Giovanni Vagnoli, G. A. Zampogna, S. Camarri, F. Gallaire, P. G. Ledda
Summary: This article investigates the stability of the vertical path of a permeable disk in a viscous fluid through linear stability analysis. It is found that as the disk permeability increases, the recirculation region associated with the flow velocity of the vertical steady path shrinks and eventually disappears. Additionally, the permeability progressively filters out the instability caused by wake dynamics, leading to the quenching of all linear instabilities.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Mechanical
Antonia Tirri, Alessandro Nitti, Javier Sierra-Ausin, Flavio Giannetti, Marco D. de Tullio
Summary: In this work, a novel approach for linear stability analysis of fluid-structure interaction problems is presented. The method combines a validated immersed boundary solver with Krylov-based techniques to obtain a robust and accurate global stability solver. The proposed algorithm avoids complex analytical linearization of equations while retaining all relevant aspects of the fully-coupled fluid-structure system. Testing on various cases demonstrates good quantitative agreement with literature results.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Engineering, Aerospace
Vittorio Giannetti, Manuel Martin Saravia, Luca Leporini, Simone Camarri, Tommaso Andreussi
Summary: This paper presents a synergic experimental and numerical investigation of the breathing mode in a 5 kW-class Hall thruster. The calibrated model can predict the spatio-temporal distributions of the plasma properties with reasonable accuracy based on the discharge current signal. The augmented data obtained through the combination of experiments and calibrated model provides insights into the breathing mode oscillations and the evolution of plasma properties.