INFLUENCE OF NOSE PERTURBATIONS ON BEHAVIORS OF ASYMMETRIC VORTICES OVER SLENDER BODY

The influence of nose perturbations on the behaviors of asymmetric vortices over a slender body with a three-caliber ogive nose is studied in this paper. The tests of a nose-disturbed slender body with surface pressure measurement were conducted at a low speed wind tunnel with subcritical Reynolds number of 1×105 at angle of attack α=50°. The experiment results show that the behaviors and structure of asymmetric vortices over the slender body are mainly controlled by manual perturbation on the nose of body as compared with geometrical minute irregularities on the test model from the machining tolerances. The effect of the perturbation axial location on asymmetric vortices is the strongest if its location is near the model apex. There are four sensitive circumferential locations of manual perturbation at which bistable vortices over the slender body are switched by the perturbation. The flowfield near the reattachment line of lee side is more sensitive to the perturbation, because the saddle point to saddle point topological structure in this reattachment flowfield is unstable. Various types of perturbation do not change the perturbation effect on the behaviors of bistable asymmetric vortices.

ASYMMETRIC VORTICES FLOW OVER SLENDER BODY AND ITS ACTIVE CONTROL AT HIGH ANGLE OF ATTACK

The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant importance for both academic field and engineering area.This paper attempts to provide an update state of art to the investigations on the fields of forebody asymmetric vortices.This review emphasizes the correlation between micro-perturbation on the model nose and its response and evolution behaviors of the asymmetric vortices.The critical issues are discussed, which include the formation and evolution mechanism of asymmetric multi-vortices;main behaviors of asymmetric vortices flow including its deterministic feature and vortices flow structure;the evolution and development of asymmetric vortices under the perturbation on the model nose;forebody vortex active control especially discussed micro-perturbation active control concept and technique in more detail.However present understanding in this area is still very limited and this paper tries to identify the key unknown problems in the concluding remarks.

Recent progress on the study of asymmetric vortex flow over slender bodies

The investigations of forebody vortex flow and its flow control have great importance in both academic field and engineering application areas. A large number of papers and many review papers have been published. However in this research field of forebody asymmetric vortices, three problems such as tip perturbation effect, Reynolds number effect and flow instability are less studied and thus not understood completely. So many researches are still working on the issues in recent years. The present paper attempts to provide a review of recent research progress on first two problems. The first problem is mainly concerned with how the vortex flow evolves after tip perturbation; how to solve the problem of repeatability and reproducibility of wind tunnel testing data; how to develop a conception of active flow control technique with tip perturbation based on the study of vortex flow response to tip perturbation. For the second problem one is mainly concerned that how the asymmetric vortices are developed with the increase of Reynolds number; how to classify the vortex flow patterns in different Reynolds number regimes; how to develop an appropriate boundary layer transition technique to simulate flows at high Reynolds number in the convention wind tunnels. Finally, some important ques- tions that deserve answers are proposed in the concluding remarks.

Effect of body position on the pathogenesis of asymmetric primary open angle glaucoma

AIM： To explore the pathogenesis of asymmetric primary open angle glaucoma（POAG） in both eyes by comparing the intraocular pressure（IOP） of patients who sleep in different positions and to investigate the relationship between IOP variations and sleep positions.METHODS： One hundred and thirty-one patients with asymmetric POAG and forty-six healthy volunteers were enrolled. All participants completed a questionnaire that provided information about their sleep laterality. The cup disc ratio（C/D） and visual field defect established binocular asymmetry. The IOP of both eyes was measured using i Care parameters after the patients were asked to change body position. The ＂worse＂ and ＂better＂ eyes were identified according to the diagnosis, whereas the ＂dependent＂ and ＂independent＂ eyes were defined according to the lateral position. RESULTS： No significant difference in sleep laterality was observed between healthy people and patients with POAG（F=3.195, P=0.362）. Among the enrolled patients, the IOP of the dependent eye was always greater than that of the independent eye in the lateral position（P〈0.05）. In the patients with binocular asymmetric POAG, the questionnaire clearly showed that 85.7% of left side preferences were found their left eyes to be the worse eyes and the right eyes of 71.4% patients with a right side preference were the more serious. When the asymmetric C/D ratio was greater than or equal to 0.2, the worse eye of patients with POAG and a preferred sleeping position was the dependent eye（χ~2=16.762, P=0.001）.CONCLUSION： A higher IOP was measured in the dependent eye in the lateral position. The long-term tendency to choose a lateral sleeping position might lead the dependent eye to manifest more severe symptoms than the independent eye. Thus, the lateral sleeping position might be one cause of asymmetric POAG.

Effects of Microscopic Three-body Forces in Asymmetric Nuclear Matter

The efiects of microscopic three-body forces on the equatioil of state(EOS)and the single particle properties of isospin asymmetric nuclear matter have been studied within Brueckner-Hartree-Fock framework~[1]The microscopic three-body force model constructed from meson exchange current approach in Ref.~[2] has been extended to isospin asymmetric nuclear

Extremum Values of Asymmetric Lp-Difference Bodies for Quermassintegrals and Dual Quermassintegrals

Based on Lutwak＇s the notion of Lp-difference bodies, Wang and Ma introduced asymmetric Lp-difference bodies and gave their extremum values for volumes. In this paper, we establish the extremum value inequalities for the quermassintegrals and dual quermassintegrals of asymmetric Lp-difference bodies and their polars, respectively.

绕回转体空泡稳定性及流动控制研究与进展综述

回转体水下带攻角高速运动时,诱发附着在物面的大尺度非对称云状空泡流动,空泡末端云状局部空泡界面失稳诱发高量值脉动压力对回转体结构强度产生重要影响,是工程研制面临的重要基础性难题。本文对绕回转体非对称云状空泡流相关研究情况进行梳理,详细地介绍在非对称云状空泡流实验和数值模拟方法、非对称云状空泡流场结构与界面稳定性、流动调控机制等方面的研究情况,并分析未来发展趋势,给出后续需要重点关注的研究方向的建议。

三馆合一项目复杂体型建筑结构设计难点与对策

广东省三馆合一项目外形宛如一艘满载艺术宝盒的巨轮扬帆起航。新颖的建筑造型使结构具有不对称复杂连体、高大空间斜幕墙、大跨度转换等结构设计难点,结构采用钢桁架与钢筋混凝土框架-剪力墙结构相结合的结构体系。分析了地震作用下连体结构连接体变形协调和塔楼间内力分配特点,并提出一系列有针对性的设计措施;结合高大空间斜幕墙的特点,利用幕墙立柱和横梁共同组成双向受力刚性结构体系,提出H型钢梁空间斜交网格幕墙结构体系,分析了幕墙结构对主体结构侧向刚度及竖向构件内力的影响,并提出设计对策;针对由于道路隧道下穿地下一层造成托换结构跨度大、托换层数多的特点,采用合理的结构形式,并提出合理的抗震性能要求及节点构造形式。

A physical model of asymmetric vortices flow structure in regular state over slender body at high angle of attack

In subcritical Reyolds number flow region, the repeatable and determinate asymmetric vortices flow at regular state can be obtained by manually setting mini-perturbation on the nose of a pointed ogive-cylinder model at high angle of attack and zero side slip. Test results of this study involve surface pressure distributions, sectional-side-force distributions and flow visualizations. The analyses of these results revealed a complicated multi-vortices system at regular state inwhich asymmetric twin vortices with inception region and fully developed region, asymmetric triple vortices, four vortices region, five vortices region and Karman-vortex-street-like flow region aredeveloped along the slender body. The correlation between multi-vortices system structures and corresponding sectional-side-force distribution is given. The behaviors of multi-vortices flow struc-ture at the peculiar points of sectional-side-force distributions and characteristics of corresponding pressure distribution are analysed. Finally, a physical model of asymmetric multi-vortices flowstructure in regular state over slender body is developed.

Mechanism of perturbation-combined active control technique for asymmetric vortex flow over slender body at high angle of attack

Based on the determinability of asymmetric vortices flow over slender body under changeless round grain at high angle of attack,the effect of microblowing set in special position on the behaviors of asymmetric flow is discussed in this paper,including blowing momentum and circumferential locations of the microblowing hole of 0.5 mm in diameter on nose tip.A new kind of active control technique,named perturbation-combined active control technique,which combines the micro-grain and micro-blowing perturbation,was proposed on the basis of the above.This control technique can not only change the sign of side force of slender body arbitrarily through changing the vortices positions between yaw-left and yaw-right configuration,but also can make the magnitude of side force variable gradually even at bistable state of asymmetric vortex.Finally,the interferential mechanism of the perturbation-combined active control technique has also been concluded from this paper.The tests have been conducted at low speed wind tunnel with subcritical Reynolds number of 1.05×10~5 at angle of attack α=50° in Beihang University,Beijing,China.

细长体大迎角非对称涡流的数值研究

通过数值方法对大迎角细长体低速湍流流场的模拟,探讨头部顶端极小扰动对细长体非对称绕流形成与发展的影响.结果表明在细长体顶端附近施加极小扰动可以模拟出实验观测到的非对称流场,非对称的涡系结构沿轴向是逐步发展的,截面侧向力沿轴向的分布呈现正弦型曲线的变化特征,扰动能量经过指数增长后达到饱和,有效扰动的规模影响涡流非对称性的大小及分布,单侧扰动产生的流场非对称性随扰动周向位置的变化呈现单周期性规律.小扰动诱发非对称的数值算例表明非对称绕流的形成是源于流场的空间不稳定性机制.

滨江水体水环境容量计算研究

针对滨江水体感潮特性明显、水流运动复杂等特点,考虑污染物质输运过程平面分布的不均匀性,提出了基于非均匀分布系数的水环境容量计算方法;以镇江内江为研究区域,建立了二维水流水质耦合数学模型.通过对内江2004年4月及8月两个典型全日潮流场特征及相应污染物迁移扩散过程的数值模拟,建立了排污量与污染带响应关系曲线,求得内江洪、枯两季非均匀分布系数分别为0.18与0.25;对内江不同水位条件及不同典型年水环境容量进行计算.结果表明,内江维持水位对其水环境容量影响较大,洪季维持平均水位4m时的容量值约比1m时增加了33.5%;不同典型年,内江水环境容量相差也较大,丰水年容量值较平水年增加了110%,而枯水年则比平水年减少了32.8%;各年内总容量的84%主要分布在5月至10月.该方法运用非均匀分布系数综合体现了滨江水体水动力条件复杂及潮汐作用下污染物迁移扩散规律多变对水环境容量的影响.

Re数对细长旋成体非对称涡及气动力特性影响的实验研究

通过对细长拱柱旋成体大迎角绕流不同截面测压结果分析,探讨了绕流Re数对非对称涡结构和气动特性的影响,得出Re数不仅影响分离线位置和绕流流态结构,而且影响边界层的绕流特征及其分离涡的强度,非对称性的出现与细长体两侧边界层的绕流特征和分离涡的强度不等存在密切的关系。特别是在同种流态下,两侧边界层的绕流特征和分离涡强度不等是造成侧向力的主要原因;在两侧不同的流态下,转捩不对称是产生大侧向力的主要原因。

“麦莎”台风暴雨落区非对称分布的诊断分析

利用FY-2C气象卫星资料、常规资料和NCEP再分析资料,对2005年第9号台风"麦莎"登陆后暴雨落区非对称分布的成因进行诊断分析,并讨论其动力学和热力学特征。结果表明:(1)FY-2C红外一通道辐射亮温(TBB)场能够清晰地揭示台风暴雨落区的分布以及造成这种非对称分布的云系结构特征;(2)水汽图像展示了此次降水过程中,对流层中上层主要的水汽型,来自南海和东海强盛的热带水汽羽直抵台风中心东部,中纬度地区的极锋水汽羽东移,其尾端并入台风北部,受二者共同作用,台风降水呈非对称分布;(3)台风中心附近的垂直流场、涡度、假相当位温和整层积分的水汽通量散度等物理量的非常规分布以及低层冷空气的契入,共同解释了台风云系的非对称结构及强雨区非对称分布的形成原因。

摇滚/PIV/压力同步测控技术的发展及其在机翼摇滚研究中的应用

在北航D4风洞已研制的机翼摇滚运动/流动研究组合装置的基础上,为实现在一次实验中同步测量机翼摇滚运动角位移和相应的物面压力分布及空间流动参数,发展了机翼摇滚/PIV/物面压力分布同步测控技术。基于该同步测控技术,进一步研究了前体涡诱导机翼摇滚过程中流动特性及演化规律。此外,还对同步PIV技术中粒子材料的选用进行了研究。

头部钝度对大迎角非对称多涡流动特性的影响

在西北工业大学NF 3风洞通过表面测压和物面油流实验以及在北京航空航天大学1.2m水洞利用染色线显示和激光片光技术,对尖头和钝头拱形细长体大迎角绕流结构和气动特性进行了研究。结果表明,尖头拱形细长体在大迎角下(45°≤α≤60°)表现出非对称多涡的复杂涡系流动现象,相应的截面侧向力CZ沿轴向呈现出类似正弦曲线形式的减幅振荡,并且侧向力幅值较大(1<CZ<3.5);而将尖头改为钝头,CZ的幅值比原来减小2/3(CZ<1),而且在某些滚转角下呈现侧向力分布基本为零的现象。文中分析了侧向力大幅度减小的机理,认为尖拱头部顶端变钝后,物面分离线由开式分离变为闭式分离,并且在顶端背风侧形成U形马蹄涡结构;马蹄涡的作用是约束背风侧2个主涡,抑制非对称的出现。

利用DES方法对大迎角细长旋成体气动特性受俯仰振荡影响的数值研究

采用DES(Detached-Eddy Simulation)对大攻角下细长旋成体俯仰振动的气动特性进行了数值模拟,分析俯仰振动对细长旋成体流场与气动力特性的影响。通过对背风面分离涡的强度和位置,流场形态,截面压强系数和侧向力系数的观察与分析,发现施加小振幅、特定频率的俯仰振动对大迎角细长旋成体背风面流场有明显的控制能力,将改变流场结构,使背风面非对称流场趋于对称。

头部几何微扰对流动不对称性影响的数值研究

使用低耗散的Roe格式，数值模拟了头部几何微扰对细长体不对称绕流的影响。计算发现，周向网格的加密本身也是一种微扰动，会对流场产生很大的影响。如果再加上头部几何微扰，随其高度的变化，侧向力分布显示出类似于几何扰动周向角变化时产生的双稳态现象。在对应的攻角下，头部扰动的方式决定了头部分离的方向，进而决定了后体的流场发展情况。

亚临界雷诺数细长体绕流流态随迎角的变化和分区

通过在北航1.2m水洞中利用染色液显示和激光片光技术的显示实验以及在西工大NF-3风洞中进行的表面测压实验,对拱形头部细长旋成体在无侧滑条件下的流场结构和流动特性随着迎角的变化进行了实验研究。在流动显示和测压结果分析的基础上,对迎角从0°到90°范围内绕细长体的流动进行了流态分区,即细长体绕流经历6种流态:极小迎角下(0°≤α≤3°)物面附着绕流流态、小迎角下(3°<α≤25°)背部对称旋涡流态、中等迎角下(25°<α≤40°)背部2个非对称旋涡流态、大迎角下(40°<α≤60°)的非对称多涡系复杂流态、特大迎角下(60°<α<75°)背部多个旋涡依次破裂的流态、极大迎角下(75°≤α≤90°)背部类卡门涡街(或随机尾迹)流态。阐述了不同区域的流动特性和气动特性。

细长体大迎角非对称流动的高速PIV风洞试验研究

具有细长前体构型的飞行器在大迎角绕流中会出现明显的非对称涡系流动及其伴随而来的非对称力，该现象受多种因素影响，而其中对压缩性效应的研究相对较少。在0．6m 亚跨超声速风洞中，采用 PIV 测量技术，对尖拱细长旋成体大迎角非对称流动开展了试验研究。试验 M 数范围为0．4～1．2，迎角为40°。试验结果表明：细长体模型在高速情况下仍然存在非对称多涡流动结构；Re 数和压缩性均对非对称涡流动产生明显影响；模型头尖部人工微扰动与非对称涡之间存在确定的响应关系。