Particle image velocimetry （PIV） measurements of tip vortex wake structure of wind turbine

Large-view flow field measurements using the particle image velocimetry (PIV) technique with high resolution CCD cameras on a rotating 1/8 scale blade model of the NREL UAE phase VI wind turbine are conducted in the engineering-oriented Φ3.2 m wind tunnel.The motivation is to establish the database of the initiation and development of the tip vortex to study the flow structure and mechanism of the wind turbine.The results show that the tip vortex first moves inward for a very short period and then moves out...     

The numerical solution for problems of turning point without resonance

In this paper the uniform convergence of Il in scheme to the turning point problems without resonance is provedby means of Kellogg’s method The given estimation is shown to be optimal.     

Effect of Volume Energy Supply on the Stability of a Subsonic Vortex Flow

Calculations of the stability of an axisymmetric vortex flow of viscous heat-conducting gas with volume energy supply are presented. The unperturbed axisymmetric vortex flow was found numerically using a quasi-cylindrical approximation of the Navier-Stokes equations under the assumption of constant peripheral-velocity circulation in the ambient co-current flow. The volume energy supply in the viscous vortex core was modeled by an additional source term in the energy equation. The stability characteristics of the viscous vortex flow in a longitudinal vortex with respect to both axisymmetric and non-axisymmetric three-dimensional waves traveling along the vortex axis and corresponding to both positive and negative values of the azimuthal wave number were found using the time-dependent formulation of the linear stability theory for compressible three-dimensional plane-parallel flows.     

Comparison of Two Unsteady Intermittency Models for Bypass Transition Prediction on a Turbine Blade Profile

The present paper evaluates two unsteady transition modelling approaches: the prescribed unsteady intermittency method PUIM, developed at Cambridge University and the dynamic unsteady intermittency method developed at Ghent University. The methods are validated against experimental data for the N3-60 steam turbine stator profile for steady and for unsteady inlet flow conditions. The characteristic features of the test case are moderately high Reynolds number and high inlet turbulence intensity, which causes bypass transition. The tested models rely both on the intermittency parameter and are unsteady approaches. In the prescribed method, the time-dependent intermittency distribution is obtained from integral relations. In the dynamic method, the intermittency distribution follows from time-dependent differential equations. For unsteady computations, self-similar wake profiles are prescribed at the inlet of the computational domain. Joint validation of the prescribed and the dynamic unsteady intermittency models against experimental data shows that both methods are able to reproduce the global features of the periodical evolution of the boundary layer under the influence of a periodically impinging wake. The overall quality of the dynamic method is better than that of the prescribed method.     

环空流道液流失速水击特性及其成因的研究

环空流道与圆管的结构差异,使得其失速水击特性及其成因亦有不同。为了对其进行分析研究,利用PIV对套管环空和圆管流水击流场进行拍摄,并通过Tecplot显示流场,提取轴向速度和径向速度、等速度线等参数加以分析;同时采用高精度智能动态压力传感器采集了套管环空内、外壁及内管内壁压力,对环空中水击特性进行了进一步研究。结论是:水击发生时环空断面外壁面水击压力大于内壁面水击压力;同初速情况下环空液流水击压力大于圆管流水击压力;环空中水击压力衰减速度快于圆管中;涡流是水击压力衰减以及速度变化的主要因素;水击压力振荡变化主要是压力涡流引起的断面能量的相互转化形成的。     

The existence and uniqueness of the screw tensor for the finite displacement of a rigidbody

The existence and uniqueness theorem of the screw tensor for the finite displacement of a rigidbody is proposed and then proved using the screw calculus. As a consequence, formulae are obtained for determining the screw tensor in terms of the finite displacement data of the rigidbody.     

TOPOLOGY AND VORTEX STRUCTURES OF A CURVING TURBINE CASCADE WITH TIP CLEARANCE (Ⅱ)- TOPOLOGICAL FLOW PATTERN AND VORTEX STRUCTURE IN THE TRANSVERSE SECTION OF A BLADE CASCADE

By means of ink trace visualization of the flows in conventional straight, positively curved and negatively curved cascades with tip clearance, and measurement of the aerodynamic parameters in transverse section, and by appling topology theory, the topological structures and vortex structure in the transverse section of a blade cascade were analyzed. Compared with conventional straight cascade, blade positive curving eliminates the separation line of the upper passage vortex, and leads the secondary vortex to change from close separation to open separation, while blade negative curving effects merely the positions of singular points and the intensities and scales of vortex. Foundation items: 973 Project of China; the Doctoral Foundation of Education Ministry of China (EDAF24403003) Biography: YANG Qing-hai (1969−)     

光检测器参数对相位—多普勒粒子分析系统特性的影响

应用几何光学近似理论模型计算了激光相位多普勒系统中微粒的光散射特性,得到了散射光强与粒径关系、检测器表现的散射光强分布、相位差与粒径特性中的非线性跃变以及检测器形状对特性的影响。     

Effect of Sinkhole Position Symmetry on the Formation of Nonstationary Vortex Funnels

The effect of the sinkhole position on the formation of nonstationary vortex funnels during fluid outflow from a tank whose diameter is much greater than the sinkhole diameter is studied experimentally. The devices for filling the tank were so designed that the opening of a sinkhole on the axis of a cylindrical tank immediately after it had been filled did not lead to the formation of a vortex funnel during fluid outflow. The formation of vortex funnels, when before the sinkhole was opened a disk immersed in the fluid was rotated, is investigated. In this case, a certain time after the outflow started, above the sinkhole a vortex funnel was formed. This time measured by means of digital filming depended on the sinkhole position and increased with the distance between the sinkhole and the axis. The results obtained make it possible to conclude that the symmetry strongly affects the process of vortex funnel formation.     

Asymptotic Theory of the Viscous Interaction Between a Vortex and a Plane

The problem of the viscous interaction between a flow induced by a vortex filament and an orthogonal rigid surface is solved for high Reynolds numbers using the method of matched asymptotic expansions. In view of the impossibility of matching the principal terms of the asymptotic expansions directly for the near-axial boundary layer and the main flow zone, the solution is obtained by introducing two intermediate zones. In this case a logarithmic singularity of the axial velocity arises inevitably on the vortex filament. In the near-axial and intermediate zones the solution is obtained numerically and analytically, respectively, while in the main zone the problem reduces to the problem of the flow induced by a line of weakly swirled vortex-sinks.     

The warp and stress transmission in the joint of an open thin wall beam

The regularities of the warp in the sections of an open thin-wall beam have been discussed using the MODERN ENGINEERING THEORY OF BEAM. Thus, the transmission relationship between the warp displacements and the double-moments in the joints of open thin-wall beams which are connected in different ways has been deduced. Meanwhile, experiments conducted by the author and some conclusions reached from these experiments as well as the tentative idea for further perfection are briefly presented here.Communicated by Chou Li.     

接触状态对叶根轮槽应力分布影响的研究

汽轮机叶片叶根、轮槽连接区域常因加工误差及磨损等原因导致接触状态的改变,从而改变整个区域应力分布并大大降低汽轮机的使用寿命。本文运用数字光弹性技术实验测试了长叶片叶根、轮槽在不同接触状态下的应力分布情况,同时结合有限元进行了仿真计算。结果表明,叶根、轮槽对称接触时,全部齿同时接触的应力集中系数最小且分布较均匀;而当部分接触齿产生间隙时,接触状态发生显著变化,应力集中系数明显增大;尤其是当左右齿非对称接触时,最大应力集中系数明显增大且应力分布不均匀。本文研究可为叶根、轮槽的优化设计、加工以及叶片的装配、维护提供实验依据。     

Effect of mini-flaps on the structure of the near wake behind a model half-wing

The effect of mini-flaps on the vortex structure of the near wake flow behind a model of a half-wing, rectangular in plan, is investigated. In a subsonic wind tunnel the time-average flow parameters are measured in several sections behind a model with flaps mounted on both upper and lower surfaces near the trailing edge. The wake flow parameters are compared with those for a model with no flaps. The considerable effect of the flaps on the flow structure in the viscous core of a tip vortex formed behind the model half-wing is established.     

基于PIV测量的超声波流量计内流场特性研究

采用PIV(Particle Image Velocimetry)测量手段,考察了小口径超声波流量计的流动特性。首先针对前端安装直管段时,不同流量条件下的流场特性建立基本认识,实验结果表明,在低流量条件下,流量计内流场存在明显的不稳定演变和非定常流动特征。进一步以上游前端安装球阀为典型案例,考察了安装条件对超声波流量计响应特性和测量偏差的影响。结合直管段的实验观测结果,发现此种结构超声波流量计的适应性与其流场非定常性的关系具有很好的一致性,即流场结构稳定则适应性强。此外,综合多参数的实验结果表明,雷诺数是判断小口径超声波流量计测量准确性的重要无量纲参数。     

偏转矢量喷流对双三角翼前缘涡破裂影响的实验研究

本文应用染色液流动显示技术对后缘偏转喷流情况下76°/40°双三角翼前缘涡破裂位置的变化进行了观测,实验结果表明偏转喷流主要推迟与喷流方向相同一侧前缘涡的破裂,而使另一侧前缘涡破裂略有提前.随着喷流偏转角度的增大,喷流使两前缘涡破裂位置差逐渐增大.另外,随着模型攻角的增大,前缘涡涡核与双三角翼翼面的夹角逐渐增大,导致偏转喷流的作用逐渐减弱.     

水击谐波流场中乳化油液滴粒径的PIV测量

为了掌握乳化油液滴在水击谐波流场中的碰撞、破裂、聚集和变形等微观形态的变化规律,采用粒子图像测速(PIV)技术对水平方管中乳化油液滴的水击谐波流场进行了测量,分析了在水击谐波流场中,不同激振力作用下乳化油液滴的粒径变化。测量结果表明,在水击谐波流场作用下,乳化油液滴平均粒径的增长率随着激振力的减小而减小,随着作用时间的增大呈增加趋势,直至粒径处于一种动态平衡;乳化液滴随着激振力增大到达波节聚集位置的时间减少,可见增大水击谐波激振力有利于乳化液滴的聚集并合并为大尺度的液滴,从而有效地提高了水击谐波流场作用下的油水分离效果。     

Induced flow and ascent of heavy particles when an air intake operates near a surface

The structure and the properties of the air flow developing when an intake system (in particular, a turbojet engine) operates near a surface are studied. On the basis of numerical calculations, the conditions of onset, the intensity, and the structure of the vortex flow ascending from the surface toward the intake are determined. From an analysis of the particle transport toward the intake by the vortex flow, the main factors responsible for the rise of large particles and objects are determined and the conditions of minimization of the probability of large particles entering the intake are found.     

Turbulent flow past a bubble and an ellipsoid using shadow-image and PIV techniques

An experimental investigation on flow around an oscillating bubble and solid ellipsoid with a flat bottom was conducted. A single air bubble (equivalent diameter D_e=9.12 mm) was attached to a small disk (1 mm) at the end of a needle and suspended across a vertical square channel (100 mm) by wire wherein water flowed downward at a constant flowrate. The solid ellipsoid (D_e9.1 mm) was suspended across the square channel in the same manner. The equivalent diameter-based Reynolds and Eotvos number range, 1950<Re<2250 and 11<Eo<11.5, placed the bubble in the ‘wobbly’ regime while the flow in its wake was turbulent. A constant flowrate and one bubble size was used such that flow in the wake was turbulent. Velocity measurements of the flow field around the bubble or solid were made using a one CCD camera Digital Particle Image Velocimetry (DPIV) system enhanced by Laser Induced Fluorescence (LIF). The shape of the bubble or solid was simultaneously recorded along with the velocity using a second CCD camera and an Infrared Shadow Technique (IST). In this way both the flow-field and the boundary of the bubble (solid) were measured. The velocity vector plots of flow around and in the wake of a bubble/solid, supplemented by profiles and contours of the average and root-mean-square velocities, vorticity, Reynolds stress and turbulent kinetic energy, revealed differences in the wake flow structure behind a bubble and solid. One of the significant differences was in the inherent, oscillatory motion of the bubble which not only produced vorticity in the near-wake, but as a result of apparent vorticity stretching distributed the turbulent kinetic energy associated with this flow more uniformly on its wake, in contrast to the solid.     

Flow induced on a salt waterbody due to the impingement of a freshwater drop or a water source

The particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques are used to study the flow induced on the surface of a body of saltwater when a drop impinges on its surface or when a source is present on the surface. The measurements show that the impingement of a fresh water drop causes a strong axisymmetric solutocapillary flow about the vertical line passing through the center of impact. The fluid directly below the center of impact rises upward, and near the surface it moves away from the center of impact. The flow, which develops within a fraction of second after the impact, persists for several seconds. In comparison, when a freshwater drop falls on a body of freshwater, the flow induced on the surface is much weaker and persists for a relatively shorter duration of time and the volume of water circulated is two orders of magnitude smaller. Similarly, when a fresh water source is present on a body of saltwater there is a solutocapillary flow which on the surface is away from the source and below the surface is towards the source.