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Suppression of vortex-induced vibration of a circular cylinder by Lorentz force

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Science China(Physics,Mechanics & Astronomy) 2011年第12期54卷 2248-2259页

作者： ZHANG Hui fan baochun LI HongZhi Science and Technology on Transient Physics Laboratory Nanjing University of Science and Technology Nanjing 210094 China

The electro-magnetic control of vortex-induced vibration (VIV) of a circular cylinder is investigated numerically in the exponential-polar coordinates attached on the moving cylinder for Re=150 in the paper. Compared with the fixed cylinder, the vibration of cylinder leads to the shift of stagnation point, the shear layer strength and the inertial force, which affects the hydrodynamic forces on the cylinder. The effects of the instantaneous wake geometries and the corresponding cylinder motion on the hydrodynamic forces for one entire period of vortex shed are discussed in the drag-lift phase diagram. The Lorentz force for controlling the vibration cylinder is classified into the field Lorentz force and the wall Lorentz force. The field Lorentz force decreases the lift oscillation, and in turn, suppresses the VIV, whereas the wall Lorentz force has no effect on the lift.

关键词： flow control vortex-induced vibration electro-magnetic control hydrodynamic force

Experimental and numerical studies on interactions of a spherical flame with incident and reflected shocks

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Acta Mechanica Sinica 2009年第2期25卷 173-179页

作者： Mingyue Gui baochun fan Gang Dong Jingfang Ye State Key Laboratory of Transient Physics Nanjing University of Science and Technology210094 Nanjing China State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology 100081 Beijing China

Observations are presented from experiments and calculations where a laminar spherical CH4/air flame is perturbed successively by incident and reflected shock waves. The experiments are performed in a standard shock tube arrangement, in which a high-speed shadowgraph imaging system is used to record evolutions of the flame. Numerical simulations are conducted by using second-order wave propagation algorithms, based on two-dimensional axisymmetric Navier-Stokes equations with detailed chemical reactions. Qualitative agreements are obtained between the experimental and numerical results. Under actions of incident shock waves, Richtmyer-Meshkov instability responsible for the flame deformation is induced in the flame, and the distoned flame takes a barrel shape. Then, under subsequent actions of the shock wave reflected from a planar wall, the flame takes an inclined non-symmetrical kidney shape in a symmetric cross section, which means a mushroom-like shape of the flame comes finally into being. The vorticity direction in the ring cap has been altered by the reflected shock＇s action, which makes the head of the mushroom-like flame extend quickly to the side wall.

关键词： Shock-flame interaction Flame instability -Vorticity Shock reflection

Drag reduction in turbulent channel flow using bidirectional wavy Lorentz force

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Science China(Physics,Mechanics & Astronomy) 2014年第11期57卷 2133-2140页

作者： HUANG LePing CHOI KwingSo fan baochun CHEN YaoHui Xi'an Aerospace Propulsion Institute Science and Technology on Transient Physics Laboratory Nanjing University of Science & Technology Faculty of Engineering University of Nottingham

Turbulent control and drag reduction in a channel flow via a bidirectional traveling wave induced by spanwise oscillating Lorentz force have been investigated in the *** results based on the direct numerical simulation(DNS)indicate that the bidirectional wavy Lorentz force with appropriate control parameters can result in a regular decline of near-wall streaks and vortex structures with respect to the flow direction,leading to the effective suppression of turbulence generation and significant reduction in skin-friction *** addition,experiments are carried out in a water tunnel via electro-magnetic(EM)actuators designed to produce the bidirectional traveling wave excitation as described in *** a result,the actual substantial drag reduction is realized successfully in these experiments.

关键词： bidirectional Lorentz turbulence suppression Figure vortex turbulent traveling visualization realized

Cellular structure of detonation utilized in propulsion system

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Science China(Physics,Mechanics & Astronomy) 2012年第10期55卷 1915-1924页

作者： ZHANG XuDong fan baochun GUI MingYue PAN ZhenHua Science and Technology on Transient Physics Laboratory Nanjing University of Science and TechnologyNanjing 210094China

How to confine a detonation in a combustor is a key issue of detonation applications in propulsion *** on achieving schemes,detonations applied in the combustor,including pulse detonation wave(PDW),oblique detonation wave(ODW) and rotating detonation wave(RDW),are different from that described by the classic CJ theory in fine structures and its self-sustaining *** this work,the cellular structures and flow fields of ODW and RDW were obtained numerically,and the fundamental characteristics and self-sustaining mechanisms of the detonations were analyzed and *** front consists of three parts:the ZND-like front,the single-headed triple point front and the dual-headed triple point *** structures of RDW are heterogeneous,and the cell size near the outer wall is smaller than that near the inner wall.

关键词： propulsion system fundamental characteristics self-sustaining mechanisms classic CJ theory

Numerical study of the turbulent channel flow under space-dependent electromagnetic force control at different Reynolds numbers

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Applied Mathematics and Mechanics(English Edition) 2019年第4期40卷 435-448页

作者： Daiwen JIANG Hui ZHANG baochun fan Zijie ZHAO Jian LI Mingyue GUI Science and Technology on Transient Physics Laboratory Nanjing University of Science and Technology Department of Mathematics Imperial College London

In this paper, the control of turbulent channel flow by space-dependent electromagnetic force and the mechanism of drag reduction are investigated with the direct numerical simulation(DNS) methods for different Reynolds numbers. A formulation is derived to express the relation between the drag and the Reynolds shear stress. With the application of optimal electromagnetic force, the in-depth relations among characteristic structures in the flow field, mean Reynolds shear stress, and the effect of drag reduction for different Reynolds numbers are discussed. The results indicate that the maximum drag reductions can be obtained with an optimal combination of parameters for each case of different Reynolds numbers. The regular quasi-streamwise vortex structures, which appear in the flow field, have the same period with that of the electromagnetic *** structures suppress the random velocity fluctuations, which leads to the absolute value of mean Reynolds shear stress decreasing and the distribution of that moving away from the wall. Moreover, the wave number of optimal electromagnetic force increases,and the scale of the regular quasi-streamwise vortex structures decreases as the Reynolds number increases. Therefore, the rate of drag reduction decreases with the increase in the Reynolds number since the scale of the regular quasi-streamwise vortex structures decreases.

关键词： flow control drag reduction electromagnetic force turbulent channel flow

Open-loop and optimal control of cylinder wake via electromagnetic fields

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Chinese Science Bulletin 2008年第19期53卷 2946-2952页

作者： ZHANG Hui fan baochun CHEN ZhiHua DONG Gang ZHOU BenMou Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China

The experimental and numerical investigations on electromagnetic control of cylinder wake have been performed in this paper. Experiments were conducted in a rotating annular tank filled with a low-conducting electrolyte. A cylinder with an electromagnetic actuator mounted on the surface was placed into the electrolyte. Force measurements have been carried out by strain gages attached to a fixed beam to which the hydrofoil is suspended and flow fields are visualized by dye markers. Based on the Navier-Stokes equations considering the electromagnetic body force, i.e. Lorentz force, in the ex- ponential-polar coordinates, the numerical investigations were carried out by means of an Alterna- tive-Direction Implicit algorithm and a Fast Fourier Transform algorithm. Experimental results have shown the same tendency with the numerical results. For the constant Lorentz forces, called open-loop control, the vortex shedding was fully suppressed. Meanwhile, the weak street disappeared and the drag force was reduced. Based on the Navier-Stokes equations, an adjoint-based ensemble optimiza- tion of control algorithms was developed and adjoint equations in the exponential-polar coordinates were derived. The equations were solved by numerical algorithm as mentioned above. The evolutions of the flow field in the control process were discussed according to the calculated variable optimal interaction parameters.

关键词：圆柱尾流电磁流最佳控制设计电磁域

Mechanism of drag reduction by spanwise oscillating Lorentz force in turbulent channel flow

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Theoretical & Applied Mechanics Letters 2012年第1期2卷 67-70页

作者： Leping Huang baochun fan Dongjie Mei Science and Technology on Transient Physics Laboratory Nanjing University of Science and TechnologyNanjing 210094China

Numerical simulations and experimental research are both carried out to investigate the controlled effect of spanwise oscillating Lorentz force on a turbulent channel flow. The variations of the streaks and the skin friction drag are obtained through the PIV system and the drag measurement system, respectively. The flow field in the near-wall region is shown through direct numerical simulations utilizing spectral method. The experimental results are consistent with the numerical simulation results qualitatively, and both the results indicate that the streaks are tilted into the spanwise direction and the drag reduction utilizing spanwise oscillating Lorentz forces can be realized. The numerical simulation results reveal more detail of the drag reduction mechanism which can be explained, since the spanwise vorticity generated from the interaction between the induced Stokes layer and intrinsic turbulent flow in the near-wall region can make the longitudinal vortices tilt and oscillate, and leads to turbulence suppression and drag reduction.

关键词： turbulent control channel flow drag reduction Lorentz force direct numerical simulation

Influences of Lorentz force on the hydrofoil lift

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Acta Mechanica Sinica 2009年第5期25卷 589-595页

作者： Yaohui Chen baochun fan Zhihua Chen Hongzhi Li Laboratory of Transient Physics,Nanjing University of Science and Technology,210094 Nanjing, China Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing China

In this paper, Lorentz forces are proved to be able to suppress separation in flows over hydrofoils. Furthermore, a differential equation of pressure distributions on the hydrofoil surface is derived, from which it is found that BVF （boundary vortex flux） σ is a suitable criterion for describing the lift coefficient variations during the electromagnetic control process. According to our numerical results, the periodic variations of lift for a hydrofoil at an attack angle of 17 ° are analyzed and its inherent mechanism is discussed in detail with the concept of BVE On the other hand, the effects of Lorentz force on the hydrofoil＇s lift are investigated both experimentally and numerically for different magnitudes and locations.

关键词： Lorentz force Lift coefficient Hydrofoil

Flow pattern and lift evolution of hydrofoil with control of electro-magnetic forces

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Science China(Physics,Mechanics & Astronomy) 2009年第8期52卷 1364-1374页

作者： CHEN YaoHui fan baochun CHEN ZhiHua LI HongZhi National Key Laboratory of Transient Physics Nanjing University of Science&TechnologyNanjing 210094China

The initial responses and evolutions of the flow pattern and lift coefficient of a hydrofoil under the action of electro-magnetic (Lorentz) force have been studied experimentally and numerically, and trace particle methods are employed for them. With the introduction of BVF (boundary vortex flux), the quantitative relation among Lorentz forces, BVF and lifts is deduced. The influences of flow patterns on the hydrofoil lift coefficient have been discussed based on the BVF distribution, and the flow control mechanism of Lorentz force for a hydrofoil has been elucidated. Our results show that the flow pattern and lift of the hydrofoil vary periodically without any force. However, with the action of streamwise Lorentz forces, the separation point on the hydrofoil surface moves backward with a certain velocity, which makes the flow field steady finally. The streamwise Lorentz force raises the foil lift due to the increase of BVF intensity. On the other hand, Lorentz force also increases the hydrofoil surface pressure, which makes the lift decrease. However, the factor leading to the lift enhancement is determinant, therefore, the Lorentz force on the suction side can increase the lift, and the stronger the Lorentz force, the larger the lift enhancement. Our results also show that the localized Lorentz force can also both suppress the flow separation and increase the hydrofoil lift coefficient, furthermore, the Lorentz force located on the tail acts better than that located on the front.

关键词： Lorentz force hydrofoil wake flow control

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