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Three-Dimensional Instability of Flow Around Two Circular Cylinders in tandem arrangement

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China Ocean Engineering 2005年第1期19卷 73-82页

作者：邓见任安禄邹建锋 Department of Mechanics Zhejiang University Hangzhou 310027 China

The spatial evolution of vortices and transition to three-dimensionality in the wake of two circular cylinders in tandem arrangement have been numerically studied. An improved virtual body method developed from the virtual boundary method is used here. A Reynolds number range between 220 and 270 has been considered, and the spacing between two cylinders is selected as L/D=3 and L/D=3.5. When L/D=3, the secondary vortices of Mode-A are seen to appear at Re=240 and persist over the range of the Reynolds number of 240～270. When L/D=3.5, the similar critical Reynolds number has been found at Re=250. No obvious discontinuity has been found in the Strouhal-Reynolds number relationship, and this is different from three-dimensional flow around a single cylinder at the critical Reynolds number. The spanwise wavelength is about four times the diameter of the cylinder, and it is the characteristic wavelength for Mode-A instability. This paper can give some foremost insight into the three-dimensional instability of flow by complicated geometrical configuration.

关键词： three-dimensional instability Mode-A instability virtual boundary method flow circular cylinders tandem arrangement

Experimental Study on Interference Effect of Three Risers Arranged in tandem with Variable Spacing Ratios

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China Ocean Engineering 2023年第3期37卷 408-419页

作者： ZHANG Peng LIU Li-hua LIU Ming REN Xiao-hui WANG Yu School of Civil Engineering Qingdao University of TechnologyQingdao 266520China College of Civil Engineering and Architecture Shandong University of Science and TechnologyQingdao 266590China Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation Qingdao 266590China School of Petroleum Engineering China University of Petroleum(East China)Qingdao 266580China

Taking the three-riser group arranged in tandem as the research subject,an experimental study was carried out on the risers arranged in tandem.The purpose is to explore the sensitivity of the dynamic response of each riser to spacing ratio and reveal the physical mechanism of riser groups under the interference effect.The spacing ratios of the adj acent risers are 4.0,5.0,6.0,and 8.0.At the spacing between the risers of 4.0D,the strong feedback effect increases the cross-flow(CF) displacement amplitude of the upstream riser.The shielding effect is the key factor affecting the interference effect on the midstream and downstream risers.At low reduced velocities,the shielding area initially appears,the displacement amplitude of the midstream and downstream risers varies greatly,the vibration of the two risers is still dominated by the first-order mode,and the transition between adjacent vibration modes is restrained.The multi-frequency superposition phenomenon is very significant at high reduced velocities.The most sensitive interference spacing under the test conditions is obtained.Due to the separation of the incoming flow and the double shielding effect of the upstream and midstream risers,the regular vortex-induced vibration in the wake area of the downstream riser is broken,and the vibration in the two directions is weakened.In general,the interference effect is more significant for the CF vibration of the three-riser groups than the in-line(IL) vibration.

关键词： three-riser group tandem arrangement vortex-induced vibration wake interference variable spacing ratios

Experimental Study on Vortex-Induced Vibration Coupling Wake Interference of Multi-Riser Groups with Sensitive Spacing

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China Ocean Engineering 2022年第3期36卷 333-347页

作者： WANG Yu LI Peng LIU Yu CHEN Xin LOU Min GUO Hai-yan College of Architecture and Civil Engineering Shandong University of Science and TechnologyQingdao 266590China Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation Qingdao 266590China School of Petroleum Engineering China University of Petroleum(East China)Qingdao 266580China College of engineering Ocean University of ChinaQingdao 266100China

The“riser group−fluid between risers”is taken as the carrier,and the experiment on vortex-induced vibration of tandem riser groups coupling interference effect under sensitive spacing is performed.The least-square method is used to linearly fit the reduced velocity and main frequency,and the rule of Strouhal numbers is analyzed.Each mode is separated based on the mode decomposition theory,and the mode conversion mechanism is also explored.The concept of“interference efficiency”is introduced to study the dynamic characteristics and response evolutions of different riser groups.The results show that the wake shielding effect widely exists in tandem riser groups,and the interference effect of midstream and downstream risers on their upstream risers is significantly lower than that of upstream risers on midstream and downstream risers.The trajectories of midstream and downstream risers lag behind their upstream risers due to multiple shadowing effects,the vibration frequency range of downstream riser is widened and the dominant frequency is extremely unstable.Compared with the isolated riser,wake interference suppresses the vibration dis-placement of the midstream and downstream risers in the in-line direction,and enhances the displacement of upstream and midstream risers in the cross-flow direction.The interference effect of the fluid between risers at low velocities is stronger than that at higher velocities,and the cross-flow displacements of upstream risers are always in the interference enhancement region.It is urgent to pay attention to the cross-flow displacement of upstream and midstream risers in tandem riser groups considering the safety design.

关键词： vortex-induced vibration interference effect multi-riser groups sensitive spacing tandem arrangement dynamic response

Alluvial channel hydrodynamics around tandem piers with downward seepage

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Frontiers of Structural and Civil Engineering 2020年第6期14卷 1445-1461页

作者： Rutuja CHAVAN Wenxin HUAI Bimlesh KUMARC Department of Civil Engineering Maulana Azad National Institute of Technology BhopalBhopalMadhya Pradesh 462003India Department of Harbor School of Water Resources and Hydropower EngineeringWuhan UniversityWuhan 430072China Department of Civil Engineering Indian Institute of Technology GuwahatiGuwahati 781039India

In this paper,we report the turbulent flow structures and the scour geometry around two piers with different diameters.An experiment was conducted on a non-uniform sand bed with two types of tandem arrangements,namely,pier(T1)with a 75 mm front and 90 mm rear,and pier(T2)with a 90 mm front and 75 mm rear,with and without-seepage flows,respectively.A strong wake region was observed behind the piers,but the vortex strength diminished with downward seepage.Streamwise velocity was found to be maximum near the bed downstream of the piers and at the edge of the scour hole upstream of the piers.Quadrant analysis was used to recognize the susceptible region for sediment entrainment and deposition.Upstream of the piers near the bed,the moments,turbulent kinetic energy(TKE),and TKE fluxes were found to decrease with downward seepage,in contrast to those in a plane mobile bed without piers.The reduction percentages of scour depth at the rear pier compared with the front one were approximately 40%for T1 and 60%for T2.Downward seepage also resulted in restrained growth of scouring with time.

关键词： scour seepage Strouhal number tandem arrangement turbulent characteristics

Experimental and Numerical Study of Penguin Mode Flapping Foil Propulsion System for Ships

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Journal of Bionic Engineering 2017年第4期14卷 770-780页

作者： Naga Praveen Babu Mannam Parameswaran Krishnankutty Harikrishnan Vijayakumaran Richards Chizhuthanickel Sunny Ocean Engineering Indian Institute of Technology Madras Chennai 600036 India Texas A&M University College Station TX 77840 USA

The use of biomimetic tandem flapping foils for ships and underwater vehicles is considered as a unique and interesting concept in the area of marine propulsion. The flapping wings can be used as a thrust producing, stabilizer and control devices which has both propulsion and maneuvering applications for marine vehicles. In the present study, the hydrodynamic per- formance of a pair of flexible flapping foils resembling penguin flippers is studied. A ship model of 3 m in length is fitted with a pair of counter flapping foils at its bottom mid-ship region. Model tests are carried out in a towing tank to estimate the propulsive performance of flapping foils in bollard and self propulsion modes. The same tests are performed in a numerical environment using a Computational Fluid Dynamics （CFD） software. The numerical and experimental results show reasonably good agreement in both bollard pull and self propulsion trials. The numerical studies are carried out on flexible flapping hydrofoil in unsteady conditions using moving unstructured grids. The efficiency and force coefficients of the flexible flapping foils are determined and presented as a function of Strouhal number.

关键词： biomimetic propulsion flapping foil penguin locomotion Strouhal number tandem arrangement thrust coefficient

Flow characteristics of the two tandem wavy cylinders and drag reduction phenomenon

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Journal of Hydrodynamics 2013年第5期25卷 737-746页

作者：邹琳郭丛波熊灿 School of Mechanical and Electronic Engineering Wuhan University of Technology

This paper presents an extensive numerical study of 3-D laminar flow around two wavy cylinders in the tandem arrangement for spacing ratios （L/Dm） ranging from 1.5 to 5.5 at a low Reynolds number of 100. The investigation focuses on the effects of spacing ratio （L / D,,） and wavy surface on the 3-D near wake flow patterns, the force and pressure coefficients and the vortex shedding frequency for the two tandem wavy cylinders. Flows arotmd the two tandem circular cylinders are also obtained for comparison. With the spacing ratio in the range of L/Dm = 1.5 - 5.5, unlike two tandem circular cylinders, the wavy cylinders in the tandem arrangement do not have the wake interference behaviour of three basic types. The vortex shedding behind the upstream wavy cylinder occurs at a further downstream position as compared with that of the upstream circular cylinder. This leads to the weakening of the effect of the vibration of the cylinders as well as a distinct drag reduction. The effects of the drag reduction and the control of the vibration of the two wavy cylinders in tandem become more and more evident when L/Dm ≥ 4.0, with a distinct vortex shedding in the upstream cylinder regime for the two circular cylinders in tandem.

关键词： wavy cylinders tandem arrangement spacing ratio drag reduction vibration