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Chinese Journal of Aeronautics 2023年第5期36卷 18-32页

作者： Zhuming RAO Ruichao LI Peizhe ZHAO Bing WANG Dan ZHAO Qiaofeng XIE School of Aerospace Engineering Tsinghua UniversityBeijing 100084China Department of Mechanical Engineering University of CanterburyChristchurch 8041New Zealand

In this study,flame responses to acoustic disturbances with different frequencies and amplitudes were experimentally investigated in a lean premixed swirl-stabilized combustor operating at different bulk velocities.The total heat release rate fluctuations and spatial CH*chemiluminescence distributions were captured using a photomultiplier tube and high-speed camera,respectively.The results indicate that the heat release rate exhibits a relatively drastic oscillation and high-order harmonics for low-frequency disturbances.When the bulk velocity and forcing frequency were doubled simultaneously,similar flame structures were observed in the CH*chemiluminescence distributions.As the bulk velocity increases,the gain of the Flame Describing Function(FDF)extends toward the higher frequencies,and the delay time of the flame response decreases.The similarity among FDFs at different bulk velocities was effectively captured by introducing a non-dimensional parameter,defined as the ratio of the flame response delay to the forcing time scale,to replace the dimensional forcing frequency.Furthermore,the availability of the newly defined non-dimensional parameter was verified for flames with different swirl numbers,as this played an important role in determining the flame structures and associated unsteady heat release rate.

关键词： Bulk velocity Combustion instability Flame describing function strouhal number Swirling flame Swirl number

Numerical Investigation of the Pulsatile Flow of Viscous Fluid in Constricted Wall Channel with Thermal Radiation

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Advances in Applied Mathematics and Mechanics 2023年第4期15卷 1001-1022页

作者： Amjad Ali Zainab Bukhari Hamayun Farooq Zaheer Abbas Centre for Advanced Studies in Pure and Applied Mathematics(CASPAM) Bahauddin Zakariya UniversityMultan 60800Pakistan Department of Mathematics Islamia University of BahawalpurBahawalpur 63100Pakistan

The main theme of the current article is to investigate the heat transfer in the pulsatile flow of an electrically conducting viscous fluid in a constricted channel under the effect of the magnetic field and thermal radiation.The unsteady governing equations simplified for low conducting fluids are solved numerically by finite difference method using stream-vorticity function formulation.The influence of the flow parameters such as the Hartmann number(magnetic parameter),strouhal number(flow pulsation parameter),Prandtl number,and radiation parameter is studied on the relevant flow profiles.The influence of different emerging parameters on the skin friction coefficient and Nusselt number are examined,as well.In general,the profiles are observed to exhibit a relatively more regular pattern upstream of the construction than that downstream of the constriction.

关键词： Constricted channel pulsatileflow thermal radiation magneticﬁeld strouhal number Prandtl number

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

Numerical Study on the 3-D Complex Characteristics of Flow Around the Hull Structure of TLP

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China Ocean Engineering 2015年第4期29卷 535-550页

作者：谷家扬朱新耀杨建民卢燕祥肖龙飞 School of Naval Architecture and Marine Engineering Jiangsu University of Science and Technology State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University

Vortex-induced motion is based on the complex characteristics of the flow around the tension leg platform （TLP） hull. By considering the flow field of the South China Sea and the configuration of the platform, three typical flow velocities and three flow directions are chosen to study the numerical simulation of the flow field characteristics around the TLP hull. Reynolds-averaged Navier-Stokes equations combined with the detached eddy simulation turbulence model are employed in the numerical study. The hydrodynamic coefficients of columns and pontoons, the total drag and lift coefficients of the TLP, the formation and development of the wake, and the vorticity iso-surfaces for different inlet velocities and current directions are discussed in this paper. The average value of the drag coefficient of the upstream columns is considerably larger than that of the downstream columns in the inlet direction of 0°. Although the time history of the lift coefficient demonstrates a ＂beating＂ behavior, the plot shows regularity in general. The strouhal number decreases as the inlet velocity increases from the power spectral density plot at different flow velocities. The mean root values of the lift and drag coefficients of the front column decrease as the current direction increases. Under the symmetrical configuration of 45°, the streamwise force on C4 is the smallest, whereas the transverse force is the largest. The broken vortex conditions in current directions of 22.5° and 45° are more serious than that in the current direction of 0°. In addition, turbulence at the bottom of the TLP becomes stronger when the current direction changes from 0° to 45°. However, a high inlet velocity indicates a large region influenced by the broken vortex and shows the emergence of the wake behind the TLP under the same current angle.

关键词： TLP flow characteristic strouhal number hydrodynamic coefficient vorticity ISO surface

Effect of an Artificial Caudal Fin on the Performance of a Biomimetic Fish Robot Propelled by Piezoelectric Actuators

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Journal of Bionic Engineering 2007年第3期4卷 151-158页

作者： Seok Heo Tedy Wiguna Hoon Cheol Park Nam Seo Goo Artificial Muscle Research Center Konkuk UniversitySeoul 143-701Korea Department of Advanced Technology Fusion Konkuk UniversitySeoul 143-701Korea Department of Advanced Technology Fusion Artificial Muscle Research Center and Smart Robot CenterKonkuk UniversitySeoul 143-701Korea

This paper addresses the design of a biomimetic fish robot actuated by piezoeeramic actuators and the effect of artificial caudal fins on the fish robot＇s performance. The limited bending displacement produced by a lightweight piezocomposite actuator was amplified and transformed into a large tail beat motion by means of a linkage system. Caudal fins that mimic the shape of a mackerel fin were fabricated for the purpose of examining the effect of caudal fm characteristics on thrust production at an operating frequency range. The thickness distribution of a real mackerel＇s fin was measured and used to design artificial caudal fins. The thrust performance of the biomimetic fish robot propelled by fins of various thicknesses was examined in terms of the strouhal number, the Froude number, the Reynolds number, and the power consumption. For the same fm area and aspect ratio, an artificial caudal fin with a distributed thickness shows the best forward speed and the least power consumption.

关键词： LIPCA biomimetic fish robot caudal fro strouhal number Froude number Reynolds number

Evaluation of pressure oscillations by a laboratory motor

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Chinese Journal of Aeronautics 2020年第3期33卷 805-825页

作者： Roohollah TAHERINEZHAD Gholamreza ZAREPOUR Department of Mechanical Engineering University of GuilanRasht 51665-315Iran

Aeroacoustic pressure oscillation is one of the important challenges in segmented solid rocket motors with high slenderness ratio.The reason for these oscillations can be searched in vortex shedding due to grain burning surfaces, holes and slots.In this paper, a novel sub-scaled motor was used for evaluation of aeroacoustic pressure oscillations.First, the related parameters to scale down using Buckingham's Pi-theorem were determined and then the sub-scaled motor was designed and manufactured.After this, strouhal number in various grain forms and vortex shedding prediction criteria have been discussed.Then, one-dimensional linear and non-linear solution approaches have been presented.To understand the motor internal flow and vortex shedding formation, steady state computational fluid dynamic performed for seven regression steps and finally, two static tests have been performed.Results show that various definitions for strouhal number are useful only for primarily glance on vortex shedding and pressure oscillations and so CFD solution and the test program are inevitable for a correct understanding of the ballistic operational condition of the motor.Experimental results demonstrated the existence of such oscillations with frequencies nearly equal to axial modes.It seems that non-linear parameters have small effects on aeroacoustic pressure oscillation and therefore the linear solution is acceptable to obtain approximate data.Of course,it should be emphasized that linear solution represents oscillations on overall motor action time,whereas the output of non-linear solution depends on thermochemistry properties of solid propellant and combustion products.Therefore, with a non-linear solution, oscillations maybe occur in some intervals of action time.FFT(Fast Fourier Transformation) results demonstrated that although both first and second acoustic modes have been excited, the position of longitudinal oscillation has an important role on which one is dominant.

关键词： Aeroacoustic Pressure oscillation Solid rocket motor strouhal number Sub-scale Vortex shedding

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

Influence of fluid-structure interaction on vortex induced vibration and lock-in phenomena in long span bridges

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Frontiers of Structural and Civil Engineering 2016年第4期10卷 363-384页

作者： Nazim Abdui NARIMAN Institute of Structural Mechanics Faculty of Civil Engineering Bauhaus University Weimar Weimar 99423 Germany

In this paper, deck models of a cable stayed bridge are generated in ABAQUS-finite element program once using only CFD model （one-way fluid-structure interaction） and another by using both the CFD model and the CSD model together （two-way fluid-structure interaction） in a co-simulation. Shedding frequencies for the associated wind velocities in the lock-in region are calculated in both approaches. The results are validated with Simiu and Scanlan results. The lift and drag coefficients are determined for the two approaches and the latter results are validated with the flat plate theory results by Munson and coauthors. A decrease in the critical wind velocity and the shedding frequencies considering two-way approach was determined compared to those obtained in the one-way approach. The results of the lift and drag forces in the two-way approach showed appreciable decrease in their values. It was concluded that the two-way approach predicts earlier vortex induced vibration for lower critical wind velocities and lock-in phenomena will appear at lower natural frequencies of the long span bridges. This helps the designers to efficiently plan and consider for the design and safety of the long span bridge against this type of vibration.

关键词： vortex-induced vibration fluid-structure interaction strouhal number lock-in kinetic energy

Blockage effects on viscous fluid flow and heat transfer past a magnetic obstacle in a duct

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Chinese Physics B 2013年第7期22卷 346-351页

作者：张喜东黄护林 Academy of Frontier Science Nanjing University of Aeronautics and Astronautics

The effect of lateral walls on fluid flow and heat transfer is investigated when a fluid passes a magnetic obstacle. The blockage ratio β that represents the ratio between the width of external magnet M y and the spanwise width L y is employed to depict the effect. The finite volume method （FVM） based on the PISO algorithm is applied for the blockage ratios of 0.2, 0.3, and 0.4. The results show that the value of strouhal number St increases as the blockage ratio β increases, and for small β , the variation of St is very small when the interaction parameter and Reynolds number are increasing. Moreover, the cross-stream mixing induced by the magnetic obstacle can enhance the wall-heat transfer and the maximum value of the overall heat transfer increment is about 50.5%.

关键词： magnetic obstacle blockage ratio strouhal number heat transfer