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Preface: mechanical perturbations induced quench: a challenge of superconductor mechanics

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National Science Review 2023年第3期10卷 7-8页

作者： Xiaojing Zheng research center for Applied mechanics Xidian University

Superconducting materials have been gradually applied in many areas including energy,transportation,medical imaging and communication.Among them,superconducting magnets that can generate a strong magnetic field above 10 Tesla with absolute advantages of higher quality,lower energy loss,and smaller volume,have become key to the performance improvement of cutting-edge science and large-scale engineering devices such as high-energy accelerators,thermonuclear fusion reactors,

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加速管道流瞬态壁面摩擦阻力及湍流行为实验研究

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四川大学学报（工程科学版） 2012年第2期44卷 21-25页

作者：王峰 HE S ARIYARATNE C 四川大学建筑与环境学院四川成都610065 Dept. of Mechanical Eng. Univ. of Sheffield Sheffield S1 3JD UK Thermo-Fluid Mechanics Research Center Univ. of SussexBrighton BN1 9QTUK

通过对加速管道流瞬态壁面摩擦阻力及湍流行为的实验研究,并将改进的统计平均法应用于实验数据的处理。结果表明,加速管道流瞬态时均壁面切应力较稳态壁面切应力存在明显差异,工况1中最大差值接近于稳态值的2倍。流动加速率的降低和初... 详细信息

通过对加速管道流瞬态壁面摩擦阻力及湍流行为的实验研究,并将改进的统计平均法应用于实验数据的处理。结果表明,加速管道流瞬态时均壁面切应力较稳态壁面切应力存在明显差异,工况1中最大差值接近于稳态值的2倍。流动加速率的降低和初始流量的增加缩短了湍流的滞后段,减小了瞬态壁面切应力与稳态值的差别。瞬态壁面切应力及湍流的发展可分为4个典型阶段,前2个阶段为湍流的滞后期,流动惯性占据主导地位,后2个阶段为湍流的发展阶段。

关键词：加速管道流动壁面切应力湍流实验

Geometric Constraints for Global Regularity of 3D Shear Thickening fluids

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Acta Mathematicae Applicatae Sinica 2024年第1期40卷 205-210页

作者： Jia-qi Yang research&Development Institute of Northwestern Polytechnical University in Shenzhen Shenzhen518063China Key Laboratory for mechanics in fluid Solid Coupling Systems Institute of MechanicsChinese Academy of SciencesBeijing100190China

We consider the relation between the direction of the vorticity and the global regularity of 3D shear thickening fluids.It is showed that a weak solution to the non-Newtonian incompressible fluid in the whole space is... 详细信息

关键词： direction of the vorticity non-Newtonian fluid global regularity

The extractable hydrokinetic power from an oscillating membrane-based harvester

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Theoretical & Applied mechanics Letters 2019年第2期9卷 66-70页

作者： Francisco J.Arias Salvador De Las Heras Department of fluid mechanics University of Catalonia

The extractable hydrokinetic power from an oscillating membrane in standing motion and induced by a water flow and its possible significance with regard energy harvesting is discussed.The main attractiveness of such an energy harvester lies in the possibility of an inexpensive technology able to be used in those water flows which either because limitation of space(narrow channels) or a limited differential pressure drop with the surrounding but yet with a non negligible velocity are not well suited to be turbined. Utilizing a simplified geometrical model, an estimate of the extractable output density power per area of membrane was derived. Preliminary experiments were performed using a rectangular thin rubber membrane and for a typical domestic water intake as source. The experimental data quantitatively agree very well with the theoretical prediction where it was found that for water flows around 2 m/s the output power density from the membrane may be around 30 mW/cm^2 of membrane. Additional research and development is required in order to arrive at a reliable practical and commercial design.

关键词： Energy harvesting Residual waters Waste waters

Effect of pitch angle on initial stage of a transport airplane ditching

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Chinese Journal of Aeronautics 2013年第1期26卷 17-26页

作者： Guo Baodong Liu Peiqing Qu Qiulin Wang Jiawen Institute of fluid mechanics Beihang University Key Laboratory of fluid mechanics Ministry of Education Beihang University

Airworthiness regulations require that the transport airplane should be proved to ensure the survivability of the ditching for the passengers. The planned ditching of a transport airplane on the calm water is numerically simulated. The effect of pitch angle on the impact characteristics is especially investigated by a subscaled model. The Reynolds-averaged Navier-Stokes （RANS） equations of unsteady compressible flow are solved and the realizable j-e equations are employed to model the turbulence. The transformation of the air-water interface is tracked by volume of fluid （VOF） model. The motion of the rigid body is modeled by dynamic mesh method. The initial ditching stage of the transport airplane is analyzed in detail. The numerical results show that as the pitching angle increases, the maximal normal force decreases and the pitching motion becomes much gentler. The aft fuselage would be sucked down by the water and lead to pitching up, whereas the low horizontal tail prevents this trend. Consequently, the transport aircraft with low horizontal tail should ditch on the water at an angle between 10 and 12 as a recommendation.

关键词： Crashworthiness fluid structure interaction Hydrodynamics Multiphase flow Transport aircraft Water landing

Design and analysis of an untethered micro flapping robot which can glide on the water

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Science China(Technological Sciences) 2022年第8期65卷 1749-1759页

作者： CHEN YanHong LIU YiDe LIU TaiShan LI Hua QU ShaoXing YANG Wei State Key Laboratory of fluid Power&Mechatronic System Key Laboratory of Soft Machines and Smart Devices of Zhejiang ProvincesCenter for X-MechanicsDepartment of Engineering MechanicsZhejiang UniversityHangzhou 310027China

Flapping-wing flying insects possess various advantages,such as high agility and efficiency.The design and manufacture of insect-scale flapping-wing micro aerial vehicle(FWMAV)have attracted increasing attention in recent decades.Due to the limitations of size and weight,the FWMAV with an onboard battery which can fully mimic insect flight has not been achieved.In this work,we design and fabricate a highly integrated flapping-wing microrobot named Robomoth.The Robomoth consists of a carbon chassis,customized power and control devices,and two piezoelectric ceramic actuators symmetrically distributed in the thorax and controlled individually.It weighs 2.487 g,spans 5.9 cm in length,possesses 9 cm of wingspan,and carries a 0.355 g rechargeable lithium battery.We demonstrate the mobility of the Robomoth through untethered gliding and making turns on the water surface.A simplified dynamic model of the flapping system is proposed to explain the relationship between the driving frequency and the flapping amplitude.The Robomoth is one new untethered bioinspired flapping-wing robot that can perform stable water surface motion,which holds potential applications such as search and rescue on the water.The robot can also provide insight for designing insect-scale flying vehicles.

关键词： micro/nanorobots biologically inspired robots flapping-wing flying piezoelectric ceramic actuator

Numerical investigations on performance improvement mechanism of a high-power vertical centrifugal pump with special emphasis on hydraulic component matching

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Journal of Hydrodynamics 2023年第4期35卷 649-667页

作者： Gang Yang Xi Shen De-sheng Zhang Wen-hua Luo Jia Meng Xu-tao Zhao research center of fluid Machinery Engineering and Technology Jiangsu UniversityZhenjiang212013China Key Laboratory of fluid Machinery and Engineering Xihua UniversityChengdu610039China

The purpose of this paper is to investigate the performance improvement mechanism of a high power vertical centrifugal pump by using numerical calculations.Therefore,a comparative study of energy losses and internal flow characteristics in the original and optimized models was carried out with special attention to the hydraulic component matching.The optimized model(model B)was obtained by optimizing the vaned diffuser and volute based on the original model(model A),mainly the diffuser inlet diameter,diffuser inlet vane angle,volute channel inlet width and volute throat area were changed.Firstly,the comparative results on performance and energy losses of two models showed that the efficiency and head of model B was significantly increased under design and part-load conditions.It is mainly due to the dramatic reduction of energy loss PL in the diffuser and volute.Then,the comparisons of PL and flow patterns in the vaned diffuser showed that the matching optimization between the model B impeller outlet flow angle and diffuser inlet vane angle resulted in a better flow pattern in both the circumferential and axial directions of the diffuser,which leads to the PL3 reduction.The meridian velocity Vm of model B was significantly increased at diffuser inlet regions and resulted in improvements of flow patterns at diffuser middle and outlet regions as well as pressure expansion capacity.Finally,the comparisons of PL and flow characteristics in the volute showed that the turbulence loss reduction in the model B volute was due to the flow pattern improvement at diffuser outlet regions which provided better flow conditions at volute inlet regions.The matching optimization between the diffuser and volute significantly reduced the turbulence loss in volute sections 1–4 and enhanced the pressure expansion capacity in sections 8–10.

关键词： High-power vertical centrifugal pump performance improvement mechanism hydraulic component matching flow pattern energy balance equation

Predicting near-wall turbulence with minimal flow units in compressible turbulent channel flows

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Chinese Journal of Aeronautics 2023年第8期36卷 24-31页

作者： Ming YU Yalu FU Zhigong TANG Xianxu YUAN Chunxiao XU State Key Laboratory of Aerodynamics China Aerodynamics Research and Development CenterMianyang 621000China Key Laboratory of Applied mechanics of Ministry of Education Institute of Fluid MechanicsDepartment of Engineering MechanicsTsinghua UniversityBeijing 100084China

Mach number effects on the near-wall turbulence in the absence of outer motions remain unclear so far.The present study extends the Minimal Flow Units(MFUs),a widely applied method to investigate near-wall turbulence free from the impact of large-scale motions in the outer region in incompressible channel flows,to compressible wall-bounded turbulence.The compressible near-wall turbulence in MFU proves accurate in replicating near-wall statistics,independent of Mach number and statistically equivalent to the universal signals extracted from the full-sized channel.It is further utilized as universal signals in the predictive models of compressible near-wall turbulence,which is capable of accurately predicting variances and joint probability density functions of velocity and temperature fluctuations.

关键词： Turbulent flow Direct numerical simulation Supersonic flow Boundarylayerflow Mach number effects

Three-dimensional human thermoregulation model based on pulsatile blood flow and heating mechanism

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Chinese Physics B 2018年第11期27卷 278-288页

作者：党思娜薛红军张晓燕瞿珏钟诚文陈思宇 Department of fluid mechanics School of Aeronautics Northwestern Polytechnical University

A three-dimensional thermoregulation mathematical model of temperature fluctuations for the human body is developed based on predecessors＇ thermal models. The following improvements are necessary in real situations： ellipsoids and elliptical cylinders are used to adequately approximate body geometry, divided into 18 segments and five layers; the core layer consists of the organs; the pulsation of the heart cycle, the pulsatile laminar flow, the peripheral resistance, and the thermal effect of food are considered. The model is calculated by adopting computational fluid dynamics（CFD） technology, and the results of the model match with the experimental data. This paper can give a reasonable explanation for the temperature fluctuations.

关键词： thermoregulation pulsating laminar flow heat transfer computational fluid dynamics （CFD）