Article
Mechanics
Xiangjun Shan
Summary: This study systematically investigates the fluid dynamics and flow structures around a cylinder with a smaller diameter placed in the wake of another cylinder with a larger diameter. The analysis focuses on how different ratios of d/D and L/D influence the Strouhal number, wake topology, and fluid forces on the downstream cylinder. The research identifies different vortex shedding modes and discusses the impact of secondary vortex shedding on the lift coefficient.
Article
Mechanics
Hamidreza Eizadi, Hongwei An, Tongming Zhou, Hongjun Zhu, Liang Cheng
Summary: This study uses direct numerical simulations to investigate the flow over six tandem circular cylinders at different Reynolds numbers and gap ratios. The aim is to understand the vortex transitions and explore the mechanisms behind them. Four flow regimes are identified based on vortex shedding frequency, flow patterns, and force coefficients. The transitions from primary to secondary vortices involve shear layer instabilities and vortex merging, while the transitions from secondary to tertiary vortices only involve vortex merging. The onset locations of the transitions are influenced by the Reynolds number and gap ratio.
Article
Mechanics
Ming Zhao, Abdullah-Al Mamoon, Helen Wu
Summary: The simulation of flow past two wall-mounted square cylinders in a tandem arrangement reveals significant effects of gap between the cylinders on the wake dynamics. A small gap leads to reattachment of free shear layers from the upstream cylinder onto the downstream cylinder, resulting in a downwash behind it, while a large gap results in weaker variation in downstream cylinder's wake due to lack of flow separation.
Article
Mechanics
Viet Dung Duong, Van Duc Nguyen, Van Tien Nguyen, Ich Long Ngo
Summary: The flow around three elliptic cylinders with equal spacing and aspect ratio in tandem arrangements was investigated through direct numerical simulation. The study found that the flow is highly sensitive to the spacing ratio and Reynolds number, resulting in five distinct flow regimes. In the latter two regimes, two vortex shedding frequencies for the middle and downstream cylinders were observed, indicating significant wake interference.
Article
Engineering, Mechanical
Xiantao Fan, Yang Wang, Wei Tan
Summary: The research focuses on the flow-induced vibration of tandem cylinders in an oncoming flow, proposing a mathematical model to simulate vibration responses and revealing the interference mechanism between the two cylinders, accurately predicting key vibration parameters.
INTERNATIONAL JOURNAL OF MECHANICAL SCIENCES
(2021)
Article
Mechanics
Jitao Zhang, Hongmiao Jing, Mengjiao Han, Chunfang Yu, Qingkuan Liu
Summary: This study investigates the influence of taper ratio on the aerodynamic characteristics of tandem square cylinders through large eddy simulations. The results show that the taper ratio significantly affects the mean force, fluctuating force, surface pressure, and vortex shedding frequency of the cylinders. The flow separation location of the upstream cylinder is not affected by the taper ratio, but the reattachment location and width of the shear layer on the leeward surface of the downstream cylinder are influenced.
Article
Mechanics
Bo Yang, Bingchen Liang, Qin Zhang, Xun Meng, Kraposhin Matvey, Andrey Epikhin
Summary: The study investigates the flow mechanisms around two cylinders in tandem arrangement above a scoured bed using numerical simulations. Different spacing ratios between cylinders result in distinct vortex shedding characteristics, hydrodynamic forces, and lift coefficients. The effects of the scoured bed and inlet boundary layer on the flow behavior are significant, leading to changes in lift forces and drag inversion compared to wall-free conditions.
Article
Nanoscience & Nanotechnology
Qingxiang Shui, Cuie Duan, Daguo Wang, Zhaolin Gu
Summary: The numerical study of flows around tandem square cylinders at Re = 100 revealed six distinct flow regimes, with investigations into the effects of L/D on flow structures and parameters. The study also analyzed variations in physical flow parameters for different L/D values, identifying significant jumps in parameters at L/D = 4.4-4.5 due to vortex impingement. Additionally, insights were derived from simulation results on the relationship between CL-upA, CL-up ', and phi, revealing how flow patterns change from in-phase to anti-phase vortex shedding.
Article
Engineering, Marine
Hongfu Zhang, Tingting Liu, Kam Tim Tse, Huanxiang Gao, Lei Zhou
Summary: A numerical investigation is conducted on the flow past two transversely oscillating cylinders in a tandem arrangement. The results show that the fluid forces and flow structures are sensitive to the oscillation amplitude and gap, and a competition of the lift forces and a transition of vortex modes are observed. This research enhances the fundamental understanding of flow-induced forces and the interaction between a flow and tandem square cylinders.
Article
Engineering, Civil
Tian Li, Takeshi Ishihara
Summary: In this study, the effects of mass ratio, spacing ratio, and helical wires on the wake galloping of tandem circular cylinders were investigated using LES turbulence model. It was found that helical wires can effectively suppress wake galloping and reduce vibration amplitude.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2021)
Article
Mechanics
Jia Tang, Yang Yang, Mingshui Li
Summary: This paper investigates the 2D AAFs of rectangular 5:1 cylinders within different turbulent flow fields. The 2D AAF is determined by removing the influence of the 3D effect from the traditional AAF, which can be derived based on the ratio of the one-dimensional fluctuating force spectrum to the one-dimensional turbulent wind spectrum. The traditional AAF values vary in response to the 3D effect and the dimensionless turbulent integral scale in different turbulent flow fields. The 2D AAF effectively reduces the discrepancies caused by the dimensionless turbulent integral scale.
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
Mechanics
Hongjun Zhu, Jiawen Zhong, Tongming Zhou
Summary: This study investigated the flow around three isodiametric circular cylinders in an in-line configuration and found that the wake structure evolves with increasing spacing ratio, leading to different flow regimes. The wake interference is observed in the latter flow patterns, affecting the lift fluctuation and vortex shedding characteristics. The transition between different regimes also results in variations in fluid forces and shedding frequencies.
Article
Mechanics
M. R. Rastan, Md Mahbub Alam
Summary: This paper investigates the flow transitions and regimes of two tandem cylinders under different Reynolds numbers and cylinder center-to-center spacing conditions. The study identifies the effects of flow interference on various flow transitions and provides guidance for future research.
Article
Mechanics
Bing Zhao, Mengmeng Zhang, Shixiao Fu, Xuepeng Fu, Tongxiao Sun, Bin Song
Summary: An experimental investigation was conducted on the vortex/wake-induced force of double unequal-diameter cylinders in tandem. The results revealed that the downstream cylinder has smaller wake-induced force and excitation coefficients compared to a single cylinder, while the added mass coefficient increases. Furthermore, the downstream cylinder can absorb a higher proportion of energy from the wake and exhibit larger vibration amplitudes, particularly in the in-line direction.
Article
Mechanics
Zaka Muhammad, Md Mahbub Alam, Bernd R. Noack
Summary: The thrust and efficiency of a pitching foil can be enhanced by adjusting the pitching waveform. Previous studies have shown that non-sinusoidal waveforms can improve either thrust or efficiency, but not both at the same time. Inspired by nature, researchers have developed a novel asymmetrical sinusoidal pitching motion that combines two sinusoidal motions with different periods. This motion enhances both thrust and efficiency, and displays similarities with fish locomotion and predator-prey interactions.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Marine
Hongjun Zhu, Quanyu Chen, Tao Tang, Md. Mahbub Alam, Tongming Zhou
Summary: This study numerically investigates the flow structures and dynamic characteristics around a circular cylinder with bilateral splitter plates at a low Reynolds number of 100. The results show the presence of five vortex shedding regimes, including 2S regime, single-sided regime, wake-flapping regime, steady regime, and irregular regime. Subordinate vortices, tip vortices, and persisted vortices are also observed. The introduction of splitter plates leads to lift reduction and increased drag coefficient when the inclination angle is larger than 15 degrees.
Review
Engineering, Marine
Shafiqur Rehman, Luai M. Alhems, Md. Mahbub Alam, Longjun Wang, Zakria Toor
Summary: This article reviews the feasibility of wind and ocean power technologies and shares the acceptance and challenges in their development. It also discusses the energy harvesting techniques for onshore and offshore wind energy, as well as various forms of ocean energy. The efficiency, availability, and costs of these technologies are compared and evaluated.
Article
Thermodynamics
Honglei Bai, Zepeng Lin, Md Mahbub Alam, Fuwang Zhao
Summary: Based on flow decomposition, this study investigates the near wake flow and forced convection heat transfer around sinusoidal wavy cylinders, aiming to deepen the understanding of the relationship between near wake flow and heat transfer. Large eddy simulations are conducted for different wavelengths of the wavy cylinders, revealing intrinsic characteristics of the near wake flow and heat transport. The results show that heat transport in the near wake is mainly associated with coherent spanwise vortices and the temporal random stresses. Moreover, the contributions of spatiotemporal random and temporal dispersive heat fluxes are analyzed in the near wake of different wavy cylinders.
INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER
(2023)
Article
Engineering, Marine
Md. Mahbub Alam
Article
Multidisciplinary Sciences
Talaat Abdelhamid, Ahmed G. Rahma, Md. Mahbub Alam, Rongliang Chen, Md. Islam, Qiang Zhou, Hongjun Zhu
Summary: The aim of this study is to investigate the fluid flow and heat transfer characteristics of an isothermal cylinder with a curved corner radius ratio of 0.5, and an attack angle (α) ranging from 0° to 45°. The cylinder is exposed to airflow at a Reynolds number (Re) of 180 and Prandtl number (Pr) of 0.7. The study focuses on the impact of α on fluid forces, Strouhal number, Nusselt number, flow structure, and wake bubble size. The study found that the time-mean drag and lift forces are most sensitive at critical angles of 5° and 12° respectively, and increasing α from 0° to 45° enhances heat transfer from the cylinder by approximately 12.9%.
SN APPLIED SCIENCES
(2023)
Article
Mechanics
Xiaoyu Shi, Honglei Bai, Md. Mahbub Alam, Chunning Ji, Hongjun Zhu
Summary: The effects of the spanwise wavelength of a sinusoidal wavy cylinder with an elliptic cross-section on wake structures and fluid forces were investigated numerically. Based on vortical structures, Strouhal number, wake closure length, fluid forces, streamline topologies, and spatio-temporal evolutions, five distinct flow patterns were identified. Pattern III had the minimum drag force and zero fluctuating lift force was observed in patterns III and IV. Flow pattern IV showed alternate vortex shedding over half of the wavelength of the wavy elliptic cylinder, leading to zero fluctuating lift over one complete wavelength. A thorough comparison was made between the wakes of the wavy elliptic cylinder and wavy circular or square cylinders, revealing the underlying flow physics behind the observed behaviors.
JOURNAL OF FLUID MECHANICS
(2023)
Article
Engineering, Mechanical
Md. Mahbub Alam, Guanghao Chen, Yu Zhou, Longjun Wang, Jiasong Wang, M. D. Islam
Summary: This study experimentally investigates the flow-induced vibration of a cantilevered circular cylinder in the wake of another cylinder. Measurements are conducted to simultaneously capture the downstream cylinder's vibration, vortex shedding frequency, surface pressure distribution, and flow structures. It is found that the downstream cylinder with smaller ratios of diameter and spacing is more prone to galloping vibration and hysteresis in the galloping response. The importance of effective mass and damping in initiating and sustaining the vibrations is revealed. The variations in flow structures are discussed in detail in both streamwise and spanwise directions, along with fluid-structure interactions.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Engineering, Marine
Hongjun Zhu, Bing Xu, Md Mahbub Alam, Yue Gao, Tongming Zhou
Summary: This paper numerically investigates the two-degree-of-freedom VIV response of a round-ended cylinder, comparing with a circular cylinder of the same mass-damping ratio. The results indicate that the development and separation of boundary layers determine the appearance of the minimum pressure coefficient, the vortex shedding mode, and the characteristic sizes of wake structure. The reattachment and second separation of boundary layers in the round-ended cylinder contribute to a much downstream final separation point as compared to the circular cylinder.
Article
Engineering, Marine
Yu Shen, Jiasong Wang, Md. Mahbub Alam
Summary: Research on utilizing piezoelectric fiber composites to capture energy from the surrounding environment and power network nodes or micro-sensors is gaining attention. This study investigates the performance of a vertical cantilever piezoelectric water energy harvester with different cross-sections and finds that the equilateral triangular cross-section demonstrates excellent performance, achieving the best energy efficiency.
Article
Engineering, Marine
Guanghao Chen, Md. Mahbub Alam, Yu Zhou, Chunning Ji, Hongjun Zhu
Summary: This study investigates vortex-induced vibrations of an elastically supported circular cylinder under wall interference. It is found that a smaller wall-cylinder gap height ratio increases the added mass, reduces the maximum vibration amplitude, and shortens the vibration range, while enhancing the quality factor of the vibration. Decreasing the gap height ratio significantly impacts the flow structure and vortex shedding modes.
Article
Mechanics
Md. Mahbub Alam
Summary: This paper numerically investigates the optimal spacing between tubes in a tube bundle and its effects on heat transfer density. The results show that the optimum spacing depends on the tube orientations, with values of g(*)=0.5 or g(*)=0.6 yielding the maximum heat transfer density. The paper also discusses the effects of spacing on fluid forces, vortex shedding frequencies, and wake structure.
Article
Mechanics
Chongyu Zhao, Hanfeng Wang, Zhiwei Liu, Md. Mahbub Alam, Hui Tang
Summary: This paper presents an experimental study on the flow around a wall-mounted finite square cylinder with a vertically clamped flapping film. The study reveals the effects of the flapping induced vortex (FIV) on the cylinder near wake, showing that the FIVs induce more high-speed flow downwards into the wake.
Article
Construction & Building Technology
Haicheng Zhang, Qiang Zhou, Ming Li, Mingshui Li, Jingkai Xie
Summary: A novel piecewise Johnson transformation model (PJTM) is proposed to enhance the accuracy and efficiency of the estimation of non-Gaussian peak factor. The proposed PJTM, derived from the analytical formula of the unbounded system (SU system) and the semi-analytical formula of the bounded system (SB system), is applied to estimate the peak factors of non-Gaussian wind pressures on a long-span roof. The results show that the proposed PJTM has superior accuracy and efficiency compared to the commonly used models.
JOURNAL OF BUILDING ENGINEERING
(2023)
Article
Robotics
Md. Mahbub Alam
Summary: Fish, especially carps, are excellent at controlling fluid and have great maneuverability. When faced with external stimuli, fish try to escape either forward or backward, with different tail oscillations and shapes. The results provide useful insights for designing and simulating bionic fish.
INTERNATIONAL JOURNAL OF ADVANCED ROBOTIC SYSTEMS
(2023)