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A Liutex based definition and identification of vortex core center lines 预览
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作者 Yi-sheng Gao Jian-ming Liu +1 位作者 Yi-fei Yu Chaoqun Liu 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第3期445-454,共10页
Six core issues for vortex definition and identification concern with (1) the absolute strength,(2) the relative strength,(3) the rotational axis,(4) the vortex core center,(5) the vortex core size, and (6) the vortex... Six core issues for vortex definition and identification concern with (1) the absolute strength,(2) the relative strength,(3) the rotational axis,(4) the vortex core center,(5) the vortex core size, and (6) the vortex boundary (Liu C. 2019). However, most of the currently popular vortex identification methods, including the Q criterion, the criterion and the Acj criterion etc., are Eulerian local region-type vortex identification criteria and can only approximately identify the vortex boundary by somewhat arbitrary threshold. On the other hand, the existing Eulerian local line-type methods, which seek to extract line-type features such as vortex core line, are not entirely satisfactory since most of these methods are based on vorticity or pressure minimum that will fail in many cases. The key issue is the lack of a reasonable mathematical definition for vortex core center. To address this issue, a Liutex (previously named Rortex) based definition of vortex core center is proposed in this paper. The vortex core center, also called vortex rotation axis line here, is defined as a line where the Liutex magnitude gradient vector is aligned with the Liutex vector, which mathematically implies that the cross product of the Liutex magnitude gradient vector and the Liutex vector on the line is equal to zero. Based on this definition, a novel three-step method for extracting vortex rotation axis lines is presented. Two test cases, namely the Burgers vortex and hairpin vortices, are examined to justify the proposed method. The results demonstrate that the proposed method can successfully identify vortex rotation axis lines without any user-specified threshold, so that the proposed method is very straightforward, robust and efficient. 展开更多
关键词 VORTEX DEFINITION VORTEX IDENTIFICATION flow visualization Liutex Liutex MAGNITUDE GRADIENT VORTEX core LINES
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Mechanism of wavy vortex and sign laws in flow past a bluff body:vortex-induced vortex 预览
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作者 L.M.Lin S.Y.Shi +1 位作者 X.F.Zhong Y.X.Wu 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第1期1-14,I0001共15页
As reported in a previous work by Lin et al.(Acta Meeh Sin, 2018. https://doi.org/10.1007/s 10409-018-0758-z), an interesting phenomenon was discovered based on the analysis of wavy vortex and vorticity distribution i... As reported in a previous work by Lin et al.(Acta Meeh Sin, 2018. https://doi.org/10.1007/s 10409-018-0758-z), an interesting phenomenon was discovered based on the analysis of wavy vortex and vorticity distribution in the shear layers and near wake of a peak-perforated conic shroud, and two sign laws were summarized. In the present paper, the theory of a vortex-induced vortex is introduced to explore mechanisms in a wavy vortex and applicable sign laws for uniform and incompressible flow past a fixed bluff body. Based on the analysis of the nearest-wall How, two vortex-induced models for streamwise and vertical vortex pairs, respectively, are proposed under two boundary cases, denoting the induced vorticity introduced or distributed on and near the walls. As a result, the first sign law, for only streamwise and vertical components of vorticity, and the second sign law, for three components of vorticity, are obtained under their own particular conditions. The first sign law reveals the intrinsic physical relationship between streamwise and vertical vorticities, independent of the distribution of spanwise vortices in the whole flow field. It is also confirmed that the spanwise vortices, as well as the shear layers and wake width, distributed wavily across the span, are attributed to the introduced streamwise or vertical vortices. The two sign laws for vorticity are independent of the disturbed spanwise wavelength and the Reynolds number. Through the analysis of flow past the conic shroud, the two sign laws are successfully used to summarize typical spacial distributions of vorticity in three flow regions: on and near the front cylinder surfaces, the separated shear layers and the near wake. 展开更多
关键词 Wavy VORTEX SIGN LAW Vortex-induced VORTEX WAKE Bluff body
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The applicability of vortex identification methods for complex vortex structures in axial turbine rotor passages 预览
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作者 Yu-fan Wang Wei-hao Zhang +1 位作者 Xia Cao Hong-kai Yang 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第4期700-707,共8页
The complex vortex structures in the flow around turbine rotor passages, with weak or strong, large or small vortices, interacting with each other, often generate most of aerodynamic loss in turbomachines. Therefore, ... The complex vortex structures in the flow around turbine rotor passages, with weak or strong, large or small vortices, interacting with each other, often generate most of aerodynamic loss in turbomachines. Therefore, it is important to identify the vortex structures accurately for the flow field analysis and the aerodynamic performance optimization for turbomachines. In this paper, by using 4 vortex identification methods (the Q criterion, the Q method, the Liutex method and the Q -Liutex method), the vortices are identified in turbine rotor passages. In terms of the threshold selection, the results show that the D method and the Q -Liutex method are more robust, by which strong and weak vortices can be visualized simultaneously over a wide range of thresholds. As for the display consistency of the vortex identification methods and the streamlines, it is shown that the Liutex method gives results coinciding best with the streamlines in identifying strong vortices, while the Q -Liutex method gives results the most consistent with the streamlines in identifying weak vortices. As to the relationship among the loss, the vortices and the shear, except for the Q criterion, the other three methods can distinguish the vortical regions from the high shear regions. And the flow losses in turbine rotor passages are often related to high shear zones, while there is a small loss within the core of the vortex. In order to obtain the variation of vortices in the turbine rotor passages at different working points, the Liutex method is applied in 2 cases of a turbine with different angles of attack. The identification results show that the strengths of the tip leakage vortex and the upper passage vortex are weaker and the distance between them is closer at a negative angle of attack. This indicates that the Liutex method is an effective method, and can be used to analyze the vortex structures and their evolution in turbine rotor passages. 展开更多
关键词 VORTEX identification tip LEAKAGE VORTEX turbine ROTOR PASSAGE Liutex METHOD Q -Liutex METHOD
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基于速度梯度张量特征值的陷窝内旋涡分析 预览
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作者 刘静 李杰 张恒 《力学学报》 EI CSCD 北大核心 2019年第3期826-834,共9页
作为一种新型的涡流发生器,陷窝具有流动阻力小、综合传热性能高的特点,是现代高性能涡轮叶片内部冷却新技术.旋涡的定量分析是陷窝强化传热优化设计的重要依据.针对在不同陷窝模型下的旋涡结构、分离方式和背景压力变化引起的旋涡强度... 作为一种新型的涡流发生器,陷窝具有流动阻力小、综合传热性能高的特点,是现代高性能涡轮叶片内部冷却新技术.旋涡的定量分析是陷窝强化传热优化设计的重要依据.针对在不同陷窝模型下的旋涡结构、分离方式和背景压力变化引起的旋涡强度无法定量分析的问题,本文提出采用涡核速度和涡核速度梯度张量特征值来定量分析旋涡的方法.通过采用涡核处局部坐标系表示的速度矢量和速度梯度张量,得到了涡核的轴向速度、径向速度、旋转角速度、轴向加速度和径向加速度,并在此基础上简化出了用最大轴向速度、最大轴向加速度和最大旋转角速度综合表示的旋涡强度的定量分析方法.用该方法分析了不同深宽比陷窝诱导的旋涡结构,随着深宽比的增大,最大轴向速度、最大轴向加速度和最大旋转角速度均呈现明显的增大趋势,旋涡强度增大.研究表明此方法具有数据处理简单、通用性强、不受分离方式限制、不受背景压力影响的特点,且提取到的数据具有明确的物理意义,适用于各类旋涡定量分析. 展开更多
关键词 陷窝 旋涡分析 速度梯度张量 旋转角速度 旋涡强度
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Third generation of vortex identification methods:Omega and Liutex/Rortex based systems 预览
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作者 Chaoqun Liu Yi-sheng Gao +5 位作者 Xiang-rui Dong Yi-qian Wang Jian-ming Liu Yu-ning Zhang Xiao-shu Cai Nan Gui 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第2期205-223,共19页
A vortex is intuitively recognized as the rotational/swirling motion of fluids,but a rigorous and universally-accepted definition is still not available.Vorticity tube/filament has been regarded equivalent to a vortex... A vortex is intuitively recognized as the rotational/swirling motion of fluids,but a rigorous and universally-accepted definition is still not available.Vorticity tube/filament has been regarded equivalent to a vortex since Helmholtz proposed the concepts of vorticity tube/filament in 1858 and the vorticity-based methods can be categorized as the first generation of vortex identification methods.During the last three decades,a lot of vortex identification methods,including 0,A,and Aci criteria,have been proposed to overcome the problems associated with the vorticity-based methods.Most of these criteria are based on the Cauchy-Stokes decomposition and/or eigenvalues of the velocity gradient tensor and can be considered as the second generation of vortex identification methods.Starting from 2014,the Vortex and Turbulence Research Team at the University of Texas at Arlington(the UTA team)focus on the development of a new generation of vortex identification methods.The first fruit of this effort,a new Omega(/2)vortex identification method,which defined a vortex as a connected region where the vorticity overtakes the deformation,was published in 2016.In 2017 and 2018,a Liutex(previously called Rortex)vector was proposed to provide a mathematical definition of the local rigid rotation part of the fluid motion,including both the local rotational axis and the rotational strength.Liutex/Rortex is a new physical quantity with scalar,vector and tensor forms exactly representing the local rigid rotation of fluids.Meanwhile,a decomposition of the vorticity to a rotational part namely Liutex/Rortex and an anti-symmetric shear part(RS decomposition)was introduced in 2018,and a universal decomposition of the velocity gradient tensor to a rotation part(7?)and a non-rotation part(NR、was also given in 2018 as a counterpart of the traditional Cauchy-Stokes decomposition.Later in early 2019,a Liutex/Rortex based Omega method called Omega-Liutex,which combines the respective advantages of both Liutex/Rortex and Omega methods,was dev 展开更多
关键词 VORTEX definition VORTEX identification OMEGA Liutex/Rortex direct NUMERICAL simulation TURBULENCE
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PowerDrive Archer+VorteX旋转导向技术在页岩气开发中的应用 预览
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作者 霍阳 朱艳 +1 位作者 魏凯 宋波凯 《长江大学学报:自然科学版》 CAS 2019年第1期39-43,49,I0003共7页
页岩气水平井具有造斜点深、造斜率高、大井斜角、水平段长等特点,对常规定向工具提出了新的挑战。为了加快页岩气开发速度,提高机械钻速,降低井下风险,在长宁区块试验使用斯伦贝谢PowerDrive Archer+VorteX旋转导向系统。该系统搭配斯... 页岩气水平井具有造斜点深、造斜率高、大井斜角、水平段长等特点,对常规定向工具提出了新的挑战。为了加快页岩气开发速度,提高机械钻速,降低井下风险,在长宁区块试验使用斯伦贝谢PowerDrive Archer+VorteX旋转导向系统。该系统搭配斯伦贝谢PowerDrive Archer旋转导向,既能实现全旋转高造斜率导向钻进,又能通过螺杆钻具提供额外的井下动力,在提高机械钻速的前提下避免了常规螺杆钻具定向过程中摩阻过高、滑动钻进慢、容易产生不规则井眼等问题,极大地降低了后期完井作业的风险,为页岩气开发提供了新的解决方案。介绍了该系统的构成、工作原理以及现场应用情况,分析了该设备在页岩气开发的应用效果以及提速方案。 展开更多
关键词 页岩气 水平井 高造斜率 旋转导向 PowerDrive Archer VORTEX
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Safety assessment of approximate segregated parallel operation on closely spaced parallel runways
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作者 Fei LIU Xinze LIU +1 位作者 Mingjiang MOU Zhiqiang WEI 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第2期463-476,共14页
With the continuous growth of air traffic flow, some airports in China or other countries begin to construct Closely Spaced Parallel Runways(CSPR) to meet the capacity requirement of civil aviation. In this paper, the... With the continuous growth of air traffic flow, some airports in China or other countries begin to construct Closely Spaced Parallel Runways(CSPR) to meet the capacity requirement of civil aviation. In this paper, the simulation and calculation method of flight trajectory is developed,as well as the collision risk calculation method and wake vortex encounter risk calculation method.New methods for departure and go-around procedures are proposed to achieve approximate segregated parallel operation in an attempt to obtain approximately the same results on closely spaced parallel runways as on widely spaced parallel runways. By comparing with the independent parallel departure and segregated parallel operation in ICAO Doc. 9643, it is found that the lateral separation between aircraft in this proposal is not less than the separations in the other two cases. Based on the simulation calculation of flight trajectories under different conditions, the probabilities of collision conflict and encountering wake vortex are lower than those in current operation plan.The proposed plan has no special requirements in pilot operation, control command procedures,airport facilities, or meteorological observation and prediction, so it is convenient to promote and implement at the airports with closely spaced parallel runways. 展开更多
关键词 AIR traffic control AIR transportation Closely spaced PARALLEL runways Segregated PARALLEL operation WAKE VORTEX ENCOUNTER WAKE VORTEX separation standards
Diffraction of relativistic vortex harmonics with fractional average orbital angular momentum
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作者 李沙沙 沈百飞 +4 位作者 王文鹏 步志刚 张浩 张辉 翟树华 《中国光学快报:英文版》 SCIE EI CAS CSCD 2019年第5期1-5,共5页
Vortex harmonics with fractional average orbital angular momentum are genera ted when a relativistic fractional vortex beam is incident on and reflected from an over-dense plane plasma target. A two-step model is pres... Vortex harmonics with fractional average orbital angular momentum are genera ted when a relativistic fractional vortex beam is incident on and reflected from an over-dense plane plasma target. A two-step model is presented to explain the far-field patterns of the harmonics. In the Erst step, a fundamental spot-shaped hole is produced during the hole-boring stage, and harmonics are genera ted simultaneously. In the second step, differen t oTder harmonics are diffracted by the hole and propagate to the far field. This process can be accurately described by the Fraunhofer diffraction theory. This work facilitates a basic recognition of fractional vortex beams. 展开更多
关键词 RELATIVISTIC VORTEX HARMONICS FRACTIONAL AVERAGE ORBITAL angular momentum RELATIVISTIC FRACTIONAL VORTEX
电脱水器绝缘棒圆柱绕流数值模拟研究 预览
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作者 于进 杜炘洁 《油气田地面工程》 2019年第8期29-35,39共8页
使用FLUENT软件数值模拟研究原油电脱水器绝缘棒的三维圆柱绕流问题,旨在寻找合适的原油流速,使得漩涡区域最小。采用标准k-ε模型对来流速度为0.5、1.0和2.0m/s三种情况进行了模拟计算,并详细分析了计算结果,包括压力云图和速度云图等... 使用FLUENT软件数值模拟研究原油电脱水器绝缘棒的三维圆柱绕流问题,旨在寻找合适的原油流速,使得漩涡区域最小。采用标准k-ε模型对来流速度为0.5、1.0和2.0m/s三种情况进行了模拟计算,并详细分析了计算结果,包括压力云图和速度云图等。对不同流速下三维圆柱体绕流的各个截面漩涡脱落形式和速度、压力的变化情况进行分析,从而研究圆柱体绕流问题的三维效应,研究发现,通过改变区域的速度就可达到改变甚至消除卡门涡街的目的,同时也证明了FLUENT软件对不可压缩绕流计算的可行性和准确性。 展开更多
关键词 电脱水器 绝缘棒 三维圆柱绕流 FLUENT软件 数值模拟 漩涡 卡门涡街
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Cavitation vortex dynamics of unsteady sheet/cloud cavitating flows with shock wave using different vortex identification methods 预览
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作者 Chang-chang Wang Ying Liu +3 位作者 Jie Chen Fu-yi Zhang Biao Huang Guo-yu Wang 《水动力学研究与进展:英文版》 SCIE EI CSCD 2019年第3期475-494,共20页
Cavitation is a complex multiphase flow phenomenon with an abrupt transient phase change between the liquid and the vapor, including multiscale vortical motions. The transient cavitation dynamics is closely associated... Cavitation is a complex multiphase flow phenomenon with an abrupt transient phase change between the liquid and the vapor, including multiscale vortical motions. The transient cavitation dynamics is closely associated with the evolution of the cavitation vortex structures. The present paper investigates the cavitation vortex dynamics using different vortex identification methods, including the vorticity method, the Q criterion method, the Omega method (Ω), the method and the Rortex method. The Q criterion is an eigenvalue-based criterion, and in the Ω method, the parameter is normalized, is independent of the threshold value and in most conditions Ω= 0.52 . The Rortex method is based on an eigenvector-based criterion. Numerical simulations are conducted using the implemented compressible cavitation solver in the open source software OpenFOAM for the sheet/cloud cavitating flows around a NACA66 (mod) hydrofoil fixed at a = 6°,= 1.25 and Re = 7.96 × 10^5 . The flow is characterized by the alternate interactions of the re-entrant flow and the collapse induced shock wave. Results include the vapor structures and the vortex dynamics in the unsteady sheet/cloud cavitating flows, with emphasis on the vortex structures in thecavitation region, the cavity interface, the cavity closure, the cavity wakes, and the foil wakes with the shedding cavity. The comparisons of the various methods, including that the vorticity method, the Q criterion method, the Ω method, the λ2 method and the Rortex method, show the performances of different methods in identifying the cavitation vortex structures. Generally, during the attached cavity growth stage, the Q criteria can well predict the vortex structures in the cavitation region and at the foil trailing edge in the pure liquid region, while with the Ω method and the Rortex method, the vortex structures outside the attached cavity and on the foil pressure side can also be predicted. The λ2 method can well predict the vortex structures in the cavity closure region. During the re 展开更多
关键词 CAVITATION VORTEX dynamics VORTEX identification sheet/cloud cavitating flow RE-ENTRANT jet shock wave OPENFOAM
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多相混输泵叶轮不同区域增压性能 预览
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作者 史广泰 王志文 《排灌机械工程学报》 CSCD 北大核心 2019年第1期13-17,共5页
为了改善多相混输泵叶轮域的增压性能,提高混输泵叶轮的做功能力,选用标准的k-ε湍流模型,分别在纯水条件不同流量下和设计流量不同含气率下进行了数值计算,对多相混输泵叶轮不同区域的增压性能展开了研究.结果表明:从叶轮进口到出口,... 为了改善多相混输泵叶轮域的增压性能,提高混输泵叶轮的做功能力,选用标准的k-ε湍流模型,分别在纯水条件不同流量下和设计流量不同含气率下进行了数值计算,对多相混输泵叶轮不同区域的增压性能展开了研究.结果表明:从叶轮进口到出口,各级叶轮叶片工作面和吸力面压差大的区域主要集中在叶轮的前半段,且在叶轮前半段,越靠近轮缘,叶轮的增压性能越强,越靠近轮毂,叶轮的增压性能越弱,在叶轮后半段,越靠近轮缘,叶轮的增压性能越差,越靠近轮毂,叶轮的增压性能越强;在不同流量下,随着流量的增大,叶片工作面和吸力面的压差逐渐减小,流量对叶轮前半段叶轮叶片工作面和吸力面压差的影响先增大后减小,流量对叶轮后半段叶轮叶片工作面和吸力面压差的影响逐渐减小;在不同含气率下,含气率越高,对混输泵叶轮的增压性能影响越大,且随着含气率的升高,叶片工作面和吸力面压差下降越快.研究结果对多相混输泵叶轮的进一步优化设计提供重要的理论依据. 展开更多
关键词 多相混输泵 多工况 增压性能 旋涡 数值计算
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A combined application of micro-vortex generator and boundary layer suction in a high-load compressor cascade
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作者 Shan MA Wuli CHU +2 位作者 Haoguang ZHANG Xiangjun LI Haiyang KUANG 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第5期1171-1183,共13页
In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex ge... In the current study, the effects of a combined application between micro-vortex generator and boundary layer suction on the flow characteristics of a high-load compressor cascade are investigated. The micro-vortex generator with a special configuration and the longitudinal suction slot are adopted. The calculated results show that a reverse flow region, which is considered the main reason for occurring stall at 7.9° incidence, grows and collapses rapidly near the leading edge and leads to two critical points occurring on the end-wall with the increasing incidence in the baseline. As the micro-vortex generator is introduced in the baseline cascade, the corner separation is switched to a trailing edge separation by the thrust from the induced vortex. Meanwhile, the occurrence of failure is delayed due to the mixed low energy fluid and main flow. The synergistic effects between the micro-vortex generator and the boundary layer suction on the performance of the cascade are superior to the baseline at all the incidence conditions before the occurrence of failure, and the sudden deterioration of the cascade occurs at 10.3° incidence. The optimal results show that the farther upstream suction position, the lower total pressure loss of the cascade with vortex generator at the near stall condition. Moreover, the induced vortex with a leg can migrate the accumulated low energy fluid backward to delay the occurrence of stall. 展开更多
关键词 Boundary layer SUCTION Flow control strategies High-load COMPRESSOR CASCADE Numerical simulations VORTEX generators
大跨度桥梁近距离拉索风载作用的数值模拟 预览
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作者 孙亭亭 杨吉新 +1 位作者 黎建华 史言稳 《济南大学学报:自然科学版》 CAS 北大核心 2019年第2期95-100,共6页
为了研究大跨度桥梁中近距离并列拉索在脉动风场下的响应,建立桥梁并列拉索三维实体数值模型,采用MATLAB软件模拟随机脉动风场并导入流体力学计算软件Fluent中,选择计算精度较高的重整化群组理论(RNG)k-ε湍流模型作为计算模型,对近距... 为了研究大跨度桥梁中近距离并列拉索在脉动风场下的响应,建立桥梁并列拉索三维实体数值模型,采用MATLAB软件模拟随机脉动风场并导入流体力学计算软件Fluent中,选择计算精度较高的重整化群组理论(RNG)k-ε湍流模型作为计算模型,对近距离并列拉索的3种不同高度处风压分布和风速分布进行数值分析。结果表明:风压力随着高度的增加而增大,在上游拉索前端正压力最大,两侧负压力最大;最大风速出现在两索之间,在下游拉索后端不断减小,随着高度的不同,风速变化呈现规律性;在上游拉索和下游拉索之间区域的风速出现紊乱现象,主要原因是拉索距离较近,两索之间相互影响效应比较明显。 展开更多
关键词 大跨度桥梁 涡流 数值计算 并列拉索 重整化群组理论k-ε湍流模型
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Experimental investigation on aero-heating of rudder shaft within laminar/turbulent hypersonic boundary layers
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作者 Qiang LI Liang NIE +3 位作者 Kouli ZHANG Yu LI Suyu CHEN Guangsheng ZHU 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第5期1215-1221,共7页
The aero-heating of the rudder shaft region of a hypersonic vehicle is very harsh, as the peak heat flux in this region can be even higher than that at the stagnation point. Therefore, studying the aero-heating of the... The aero-heating of the rudder shaft region of a hypersonic vehicle is very harsh, as the peak heat flux in this region can be even higher than that at the stagnation point. Therefore, studying the aero-heating of the rudder shaft is of great significance for designing the thermal protection system of the hypersonic vehicle. In the wind tunnel test of the aero-heating effect, we find that with the increase of the angle of attack of the lifting body model, the increasement of the heat flux of the rudder shaft is larger under laminar flow conditions than that under turbulent flow conditions. To understand this, we design a wind tunnel experiment to study the effect of laminar/turbulent hypersonic boundary layers on the heat flux of the rudder shaft under the same wind tunnel freestream conditions. The experiment is carried out in the ?2 m shock tunnel(FD-14 A) affiliated to the China Aerodynamics Research and Development Center(CARDC). The laminar boundary layer on the model is triggered to a turbulent one by using vortex generators, which are 2 mm-high diamonds. The aero-heating of the rudder shaft(with the rudder) and the protuberance(without the rudder) are studied in both hypersonic laminar and turbulent boundary layers under the same freestream condition. The nominal Mach numbers are 10 and 12, and the unit Reynolds numbers are2.4 × 106 m-1 and 2.1 × 106 m-1. The angle of attack of the model is 20°, and the deflection angle of the rudder and the protuberance is 10°. The heat flux on the model surface is measured by thin film heat flux sensors, and the heat flux distribution along the center line of the lifting body model suggests that forced transition is achieved in the upstream of the rudder. The test results of the rudder shaft and the protuberance show that the heat flux of the rudder shaft is lower in the turbulent flow than that in the laminar flow, but the heat flux of the protuberance is the other way around,i.e., lower in the laminar flow than in the turbulent flow. The wind tunnel test results is 展开更多
关键词 Heat flux HYPERSONIC boundary layer RUDDER Shock tunnel Transition Vortex generator
Experimental Study on Influences of Surface Materials on Cavitation Flow Around Hydrofoils
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作者 Jiafeng Hao Mindi Zhang Xu Huang 《中国机械工程学报:英文版》 SCIE EI CAS CSCD 2019年第3期55-65,共11页
In order to resist on the cavitation erosion, many researchers try to change the solidity and tenacity of the coatings, but ignore the influence of surface characteristics of materials on cavitation flow and the inter... In order to resist on the cavitation erosion, many researchers try to change the solidity and tenacity of the coatings, but ignore the influence of surface characteristics of materials on cavitation flow and the interaction with each other. In this paper, high speed visualization system is used to observe the cavitation flow patterns in different stage. After comparing the characteristics of cavitation flow around hydrofoils made of aluminum (Foil A), stainless steel (Foil B) and the hydrofoil painted with epoxy coating (Foil C), the study shows that material has a significant effect on the cavitation flow. Firstly, when the incipient cavitation occurs, cavitation number of Foil A is highest among three hydrofoils, generating horseshoe vortex randomly. For Foil B and Foil C, it shows in the form of free bubbles. When the sheet cavitation occurs, Foil A has the highest cavitation number and shortest period, which is contrary to Foil C. And cavity consists of lots of small finger-like cavities. For Foil B and Foil C, it both constitutes with many bubbles. Compared with the high-density and small-scale cavities over surface of Foil C, the cavity of Foil B has larger scale and less density, which causes a minimal scope of influence of the re-entrant jet and strong randomness. When the cloud cavitation occurs, Foil C has the lowest cavitation number and shortest period. Secondly, compared with aluminum, both of stainless steel and epoxy coating restrains the occurrence and development of cavitation, and stainless steel and epoxy coating performs better than aluminum. For inception and sheet cavitation, stainless steel performs better than epoxy coating and aluminum. For cloud cavitation, epoxy coating performs better than stainless steel and aluminum. The objective of this paper is applied experimental method to investigate the effect of surface materials on cavitation around Clark-Y hydrofoils. 展开更多
关键词 CAVITATION Coating HYDROFOIL HORSESHOE VORTEX EXPERIMENT
厚度对扑动平板气动特性的影响分析 预览
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作者 陈好 石兴 蔡志俊 《工业控制计算机》 2019年第1期82-84,共3页
自然界中很多飞鸟采用扑翼飞行方式。利用二维平板模拟翅膀扑动运动,研究厚度对平板气动性能的影响。在给定的雷诺数Re、斯特劳哈数St和运动形式下,分析平板与涡的相互作用。研究发现,厚度的改变影响了涡脱落的时间以及脱落涡的强度。... 自然界中很多飞鸟采用扑翼飞行方式。利用二维平板模拟翅膀扑动运动,研究厚度对平板气动性能的影响。在给定的雷诺数Re、斯特劳哈数St和运动形式下,分析平板与涡的相互作用。研究发现,厚度的改变影响了涡脱落的时间以及脱落涡的强度。在一定厚度变化范围内,平板升力系数和推力系数幅值随厚度的增加而降低。 展开更多
关键词 扑翼 厚度 气动特性 推力系数
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Review of theoretical achievements for starting flow problem for all Mach numbers
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作者 Chenyuan BAI Juan LI +2 位作者 Sheng LI Sicheng LI Ziniu WU 《中国航空学报:英文版》 SCIE EI CAS CSCD 2019年第1期78-91,共14页
The typical behavior of unsteady flow and force evolution in a number of applications,such as aero-elastics, gust-wing interaction, flapping flight and flight maneuvering, can be understood using the starting flow mod... The typical behavior of unsteady flow and force evolution in a number of applications,such as aero-elastics, gust-wing interaction, flapping flight and flight maneuvering, can be understood using the starting flow model. Starting flow model is obtained either by setting rapidly an angle of attack for a wing moving at constant speed, or by accelerating a wing to a constant speed while gaining an angle of attack. In the limiting case of impulsively starting flow, the wing is assumed to gain suddenly an angle of attack in an initially uniform flow. Theories have been developed for impulsively starting flow at small angle of attack long before and at large angle of attack only recently, especially for incompressible and supersonic flow. This paper intends to provide a state-of-art overview of the typical flow phenomena, force evolution characteristics and developed theories for impulsively starting flow at any angle of attack and for both lower speed flow(vortex dominated) and high speed flow(compressible wave dominated). This review also provides some new topics that deserve further studies. 展开更多
关键词 Shock-shock interaction Shock WAVES STARTING FLOW UNSTEADY FLOW VORTEX
Ground-state vortex structures of a rotating binary dipolar Bose–Einstein condensate confined in harmonic plus quartic potential
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作者 陈光平 乔昌兵 +3 位作者 郭慧 王林雪 王雅君 谭仁兵 《中国物理B:英文版》 SCIE EI CAS CSCD 2019年第1期251-256,共6页
We consider a binary dipolar Bose–Einstein condensate confined in a rotating harmonic plus quartic potential trap.The ground-state vortex structures are numerically obtained as a function of the contact interactions ... We consider a binary dipolar Bose–Einstein condensate confined in a rotating harmonic plus quartic potential trap.The ground-state vortex structures are numerically obtained as a function of the contact interactions and the dipole–dipole interaction in both slow and rapid rotation cases. The results show that the vortex configurations depend strongly on the strength of the contact interactions, the relative strength between dipolar and contact interactions, as well as on the orientation of the dipoles. A variety of exotic ground-state vortex structures, such as pentagonal and hexagon vortex lattice,square vortex lattice with a central vortex, annular vortex lines, and straight vortex lines, are observed by turning such controllable parameters. Our results deepen the understanding of effects of dipole–dipole interaction on the topological defects. 展开更多
关键词 Bose–Einstein condensate dipolar–dipolar interaction HARMONIC PLUS QUARTIC POTENTIAL trap vortex structure
华南暖区暴雨事件的筛选与分类研究 预览
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作者 刘瑞鑫 孙建华 陈鲍发 《大气科学》 CSCD 北大核心 2019年第1期119-130,共12页
利用逐小时降水资料,采用客观方法对1982~2015年华南地区暖区暴雨进行了筛选和分类研究。主要结果如下:华南区域暖区暴雨事件共计177例,暖区暴雨占筛选的暴雨事件的16.86%,表明暖区暴雨是华南非常重要的降水过程。暖区暴雨主要出现在4~7... 利用逐小时降水资料,采用客观方法对1982~2015年华南地区暖区暴雨进行了筛选和分类研究。主要结果如下:华南区域暖区暴雨事件共计177例,暖区暴雨占筛选的暴雨事件的16.86%,表明暖区暴雨是华南非常重要的降水过程。暖区暴雨主要出现在4~7月,6月份最多,平均持续11.58 h。暖区暴雨事件发生位置主要集中在广东、广西的沿海地区和粤北山区,有四个降雨中心。产生华南暖区暴雨的天气形势主要有四类,切变线型、低涡型、南风型和回流型,不同类型的暖区暴雨对华南地区的内陆和沿海的作用不同,且南风影响下的暖区暴雨发生频率较高,影响较大,是一类较为重要的暖区暴雨。 展开更多
关键词 华南暖区暴雨 空间滤波 切变线 低涡
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β型斯特林发动机有限体积建模及热力学分析研究 预览
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作者 邱文会 闫春杰 王小军 《真空与低温》 2019年第3期202-208,共7页
为了研究斯特林发动机内部腔室流体流动规律,探讨不同工况对斯特林发动机做功的影响,使用基于Fluent流体计算软件的动网格模型模拟活塞和配气活塞的运动,对于回热器,采用层流流态的多孔介质模型,其他腔室使用标准k-ε模型。结果表明,在... 为了研究斯特林发动机内部腔室流体流动规律,探讨不同工况对斯特林发动机做功的影响,使用基于Fluent流体计算软件的动网格模型模拟活塞和配气活塞的运动,对于回热器,采用层流流态的多孔介质模型,其他腔室使用标准k-ε模型。结果表明,在运行周期内,腔室的局部区域存在多个涡流,这会消耗部分能量,降低热功转换效率;增加充气压力和加热器温度可以有效增加净输出功。 展开更多
关键词 斯特林发动机 动网格 有限体积 涡流
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