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Journal of Hydrodynamics 2023年第6期35卷 1089-1100页

作者： Bing Zhu Yue Li Wen-jun Xu Wei Zhang School of Energy and Power Engineering University of Shanghai for Science and TechnologyShanghai200093China National Key Laboratory of Marine Engine Science and Technology Shanghai201108China Marine Design and Research Institute of China Shanghai200011China

We have investigated the hydrodynamic and acoustic performance of a hydrofoil with a wave leading edge that is being ingested in a cylindrical wake,to explore the interaction and noise reduction mechanism with the use of near flow field and far field noise decoupled prediction methods of large eddy simulation(LES)and Ffowcs Williams-Hawkings(FW-H).Our results indicate that the wave leading edge has minimal effect on the hydrodynamic performance,however,it has demonstrated the ability to significantly improve the acoustic performance.Through the comparison of sound pressure level(SPL)and acoustic directivity,we have observed that the wave leading edge can significantly reduce the broadband noise in the far field.This is due to its ability to break the large-scale structure of the incoming flow,which weakens the direct impact and therefore reduces the tone noise.Additionally,the interaction between the broken vortex and the boundary layer around the hydrofoil surface is weakened,leading to a reduction in surface pressure pulsation and broadband noise intensity.The wave structure primarily affects the flow structure near the leading edge,resulting in a reduction in flow disturbance and sound source intensity,and an improvement in the acoustic feedback loop between the foil and the fore-cylinder.

关键词： Wave leading hydrofoil cylinder wake ingesting turbulence noise reduction large eddy simulation(LES)

CENTRIFUGAL INSTABILITY AND THE RIB VORTICES IN THE cylinder wake

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Acta Mechanica Sinica 1998年第2期14卷 104-112页

作者：张洪泉 Department of Mechanics Tianjin University Tianjin China 300072

The physical mechanism for generation of streamwise vortices (or rib vortices) in the cylinder wake was numerically investigated with a finite-difference scheme. Rayleigh's theory of centrifugal instability for inviscid axisymmetric flow was extended to analyze the 2-D primary flows. Centrifugal instability occurs when Ray greater than 0. Stability analyses were carried out with this discriminant for primary flows at different time levels in a half shedding period of the von Karman (or vK) vortices. Unstable areas were identified and the locations of rib vortices were coincident well with the unstable areas within the first wavelength of vK vortices behind the cylinder. The numerical results also show that rib vortices experience amplification in this region. (Edited author abstract) 17 Refs.

关键词： centrifugal instability rib vortex cylinder wake

Evolution of global enstrophy in cylinder wake controlled by Lorentz force

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Applied Mathematics and Mechanics(English Edition) 2008年第11期29卷 1505-1516页

作者：张辉范宝春陈志华 Laboratory of Transient Physics Nanjing University of Science and TechnologyNanjing 210094P. R. China

The Okubo-Weiss function is correlated with the fluid particle compression, deformation and vorticity, which provides a simple way to characterize different regions of a flow-field. In the present paper, it shows mathematically that the global integration of Okubo-Weiss function is always equal to zero for a two dimensional incompressible flow with no-slip boundaries. To validate the conclusion, a flow passing a circular cylinder con- trolled by the electromagnetic force is calculated numerically as an example. Distributions of global enstrophy, total squared strain and Okubo-Weiss function in the controlled flow field are discussed. The influence of Lorentz force on the distribution is analyzed.

关键词： enstrophy strain cylinder wake electro-magnetic force

Three-Dimensional Direct Numerical Simulation of Flow past A Near-Wall Circular cylinder:Combined Effects of Gap Ratio and Boundary Layer Thickness on Flow Profiles and Pressure Distribution

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China Ocean Engineering 2023年第6期37卷 948-961页

作者： YING Chao HUA Yang WEI Yu-han JI Chun-ning Zhejiang Institute of Hydraulics&Estuary(Zhejiang Institute of Marine Planning and Design) Hangzhou 310020China Shanghai Investigation Design&Research Institute Co.Ltd.Shanghai 200335China State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China

Three-dimensional direct numerical simulations of the wake flow downstream of a near-wall circular cylinder at different gap ratios and boundary layer thicknesses are carried out by using the iterative immersed boundary method.The non-dimensional gap between the cylinder and the wall,G/D=0.2,0.6 and 1.0,the non-dimensional boundary layer thickness,δ/D=0.0,0.7 and 1.6,the Reynolds number,Re=350,and the aspect ratio of the cylinder,L/D=25are adopted.High-resolution visualizations of the complex vortex structures at differentδ/D and G/D are presented.The transition of the streamwise vortex mode,the combined effects ofδ/D and G/D on the flow statistics,the pressure and shear stress distribution and the hydrodynamic forces are analyzed.Results show that with decreasing G/D and increasingδ/D,the gap flow and its vortex-shedding are significantly weakened,together with an elongated wake and an enlarged low-velocity area near the wall,leading to the wake mode transition from the two-sided to one-sided vortex-shedding.Different relative positions of the cylinder regarding the boundary layer alter the flow features of the shear layers.With an increase inδ/D,the front stagnation point shifts to the upper surface,and the distance between the flow divergence point and the maximum pressure position increases.The mean drag coefficient and r.***.s.values of drag and lift coefficients decrease with a decrease in G/D and an increase inδ/D,while the mean lift coefficient increases with decreasing G/D but decreases with increasingδ/D.

关键词： cylinder wake near-wall effect direct numerical simulation boundary layer thickness gap ratio

Underlay mechanism in lift-drag phase diagrams for shear flow over cylinder

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Applied Mathematics and Mechanics(English Edition) 2014年第2期35卷 221-228页

作者：张辉范宝春陈志华李艳玲 Science and Technology of Transient Physics Laboratory Nanjing University of Science and Technology

The characteristics of a uniform-shear flow over a circular cylinder are in- vestigated numerically by using the alternative-direction implicit （ADI） algorithm and a fast Fourier transform （FFT） one in the exponential-polar coordinates for Re = 150 and 0 ≤ K ≤ 0.46. The diagram of lift-drag phase, implying the detail information about the fluctuations of drag and lift as well as the flow patterns in the wake and fluctuating pres- sure on the cylinder surface, is used to describe the effects of the shear rate on the flow. Results show that the upper （or lower） closed curve of a phase diagram corresponds to the first （or second） half shedding cycle. The lift-drag phase diagram will move down-left with the increase of shear rate K such that the lift is exerted from the upper side to the lower side, and the drag on the first half shedding cycle is smaller than that on the second half.

关键词： shear flow cylinder wake hydrodynamic force vortex shedding

Experimental Research on the Mechanism of Lift Amplification and Vibration Suppression of Lorentz Force

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Defence Technology（防务技术） 2013年第2期9卷 110-116页

作者： ZHANG Hui FAN Baochun CHEN Zhihua LI Hongzhi LI Baoming Science and Technology on Transient Physics Laboratory Nanjing University of Science and Technology

The Lorentz force generated by electromagnetic field on the surface of the cylinder in the electrolyte solution may modify the structure of the flow boundary layer effectively. The transient control process of Lorentz force is investigated experimentally for lift amplification and vibration suppression. The experiments are conducted in a rotating annular tank filled with a low-conducting electrolyte. A cylinder with an electro-magnetic actuator is placed into the electrolyte. The lift force of cylinder is measured using the strain gages attached to a fixed beam, and the flow fields are visualized by the dye markers. The results show that the upper vortex on the cylinder is suppressed, and the wake becomes a line and leans to the lower side under the action of upside Lorentz force while the lower vortex on the cylinder is suppressed and limited in a small region. Therefore, the value of lift increases with the variation of flow field. However, the vortexes on the cylinder are suppressed fully under the action of symmetrical Lorentz force which leads to the suppression of lift oscillation and then the vibration of cylinder are suppressed fully.

关键词： hydromechanics flow control Lorentz force vortex-induced vibration cylinder wake

Experimental Study of Flow around a Circular cylinder inside a Bubble Plume

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Advances in Chemical Engineering and Science 2016年第3期6卷 269-280页

作者： Tomomi Uchiyama Yukihiro Ishiguro Institute of Materials and Systems for Sustainability Nagoya University Furo-cho Nagoya Japan Graduate School of Information Science Nagoya University Furo-cho Nagoya Japan

This study experimentally explores the flow around a cylinder with circular cross-section placed inside a bubble plume. Small gas bubbles with diameter smaller than 0.06 mm are released from electrodes on the bottom of a water tank by electrolysis of water. The bubbles induce water flow around them as they rise because of buoyancy. Inside the generated bubble plume, a cylinder with diameter D of 30 mm is placed at 6.5D above the electrodes. The bubbles and water flow around the cylinder are visualized, and the bubble velocity distribution is measured. The experiments elucidate the bubble behavior around the cylinder, the separated shear layers originating at the cylinder surface, their roll-up, the bubble entrainment in the resultant large-scale eddies behind the cylinder, and the vortex shedding from the cylinder.

关键词： Bubble Plume Separated Shear Layer cylinder wake Flow Visualization PIV