线圈形状及几何参数对电涡流传感器性能的影响

针对电涡流传感器探头线圈形状及其参数对传感器灵敏度和线性范围的影响问题，本文以Biol-Savart定律为基础，推导了具有梯形截面的矩形柱线圈和圆形柱线圈对称轴上任一点的磁场分布，确定了在以位移为检测量的电涡流传感器中采用圆柱线圈更合理，并通过有限元法研究和分析了在线圈匝数密度不变和变化2种情况下圆柱线圈内径、外径、厚度、截面形状（矩形、梯形和倒梯形）对传感器灵敏度和线性范围的影响，为合理选择线圈参数和优化传感器性能提供参考。     

掩模偏转方向对硅尖形状影响的研究

为制备高纵横比的纳米硅尖,研究了掩模的偏转方向对硅尖形状的影响。设计了硅尖制备的工艺流程,采用KOH溶液湿法各向异性腐蚀制备硅尖,将实验和{411}晶面模型相结合,分析了硅尖的成型机理,讨论了掩模偏转方向对硅尖形状的影响,得到制备高纵横比纳米硅尖的工艺参数。实验结果表明：硅尖侧壁是由与(100)面夹角为76.37°的{411}晶面组成;利用正方形掩模的偏转,可以制备出八面体和四面体的硅尖。当正方形掩模边缘沿<110>晶向时,在78℃、浓度40%的KOH溶液中腐蚀的硅尖,经980℃氧化削尖,可以得纵横比大于2的八面体纳米硅尖阵列。     

大型风机叶片气动外形参数计算及三维建模方法

结合工程实践,基于Schmitz理论计算出风机叶片气动外形参数并利用三维坐标变换原理计算截面翼型空间分布位置,在此基础上,以大型三维设计软件UG为工作平台建立了叶片三维气动外形,并完全满足五轴数控加工制造要求,从而验证了该方法的可靠性.这一方法简化了复杂曲面的设计过程,提高了工作效率,为后续的数控加工、模具制作、结构设计及计算奠定了基础.     

Enhancement of wind turbine aerodynamic performance by a numerical optimization technique

Sectional aerodynamic design optimization was performed to enhance the aerodynamic performance of horizontal axis wind turbine rotor blades based on a computational fluid dynamics technique. The proposed sectional optimization framework consists of airfoil section contour modeling by the PARSEC shape function and a modified feasible direction search algorithm. To enhance the aerodynamic performance of wind turbine rotor blades, the objective of the design framework was set to maximize the lift-over-drag ratio for each design section. A two-dimensional Navier-Stokes flow solver coupled with a transition turbulence model was used to evaluate the aerodynamic performance during the iterative design optimization procedure. The sectional flow conditions were extracted from the flow of a three-dimensional rotor blade configuration. The design framework was applied to the National Renewable Energy Laboratory Phase VI rotor blade. The design optimization was conducted at nine spanwise sections of the rotor blade. To validate the present methodology, the aerodynamic performances of the original baseline rotor and the rotor after the design optimization were compared by using a three-dimensional Navier-Stokes flow solver. It was found that approximately 11% of torque enhancement was achieved after the aerodynamic shape design optimization.     

Ti-14Nb-4Sn形状记忆合金的性能研究

为了验证Ti-14Nb-4Sn(at%)合金用于制备压力管道管接头的可行性,研究了该合金的超弹性和形状记忆效应。针对淬火温度对形状记忆合金性能具有重要影响的特点,采用了不同的淬火工艺对合金进行热处理,由弯曲试验确定了合金获得良好性能的淬火温度。通过拉伸试验对合金的超弹性进行了进一步研究与分析,发现了400℃淬火合金具有接近完全的超弹性,得到了循环拉伸可以明显改善合金超弹性的结论。研究结果表明,经过特定温度淬火后的Ti-14Nb-4Sn合金具有良好的超弹性和形状记忆效应,可作为压力管道管接头的优良选材。     

Temperature fields in the fusion zone induced by a moving electron beam

An analytical model is developed to investigate the heat transfer in the fusion zone during electron-beam welding. The keyhole produced by an electron-beam is assumed to be a paraboloid of revolution and the profile of the intensity of an electron beam is supposed to be Gaussian distribution. In order to obtain an analytical solution, a quasi-steady heat conduction Eq. is utilized to analyze the heat transfer in the workpiece and the parameter approximating convection is proposed to account for the effect of heat convection of molten metal. Considering the momentum balance at the bottom of the keyhole but neglecting the absorption in the plume, an analytical solution is obtained for semi-infinite workpieces. The effects of various parameters on the temperature distribution are also discussed in this study.     

Characteristic flow patterns and aerodynamic performance on a forward-swept wing

This investigation elucidates the effects of Reynolds number (Re) and angle of attack (??) on the boundary-layer flow patterns, aerodynamic performance, flow behaviors and vortex shedding. This investigation applies a finite NACA 0012 forward-swept wing with the forward-sweep angle (??) of 15°. The Reynolds numbers were tested in the range of 4.6 × 10⁴ < Re < 10⁵. The wing chord length is 6 cm and the semi-wing span is 30 cm, such that the full-span wing aspect ratio is 10. The surface oil-flow scheme was utilized to visualize the boundary-layer flow structures. The hot-wire anemometer was applied to measure the vortex-shedding frequency behind the forwardswept wing. Furthermore, a force-moment sensor was applied to measure the aerodynamic loadings. The surface oil-flow patterns are classified into six characteristic flow modes ?? separation, separation bubble, secondary separation, leading-edge bubble, bubble extension and bluff-body wake modes. Additionally, the output of force-moment sensor and the visualized boundary-layer flow configurations indicate that the aerodynamic performance is closely related to the boundary-layer flow behaviors. Furthermore, the boundary-layer flow stalled in the leading-edge bubble mode. Moreover, the vortex-shedding frequency behind the forward-swept wing shows that the vortexshedding frequency at low ?? exceeds that at high ??.     

车钩间隙对货运列车车钩力的影响研究

分析了一定车钩间隙下牵引杆的使用对车钩力的影响。根据讨论得出,同样工况下,车钩间隙越大车钩力越大,对列车运行越不利。牵引杆的使用可有效降低车钩力。并结合实际运用情况,给出了牵引杆的使用建议     

The aerodynamic performance of flexible wing in plunge

Inspired by the fact that flexible wing in nature possesses advance aerodynamic performance, a numerical experiment is applied to investigate the aerodynamic performance of flexible wing in plunge motion, where the incompressible Navier-Stokes (N-S) equations coupled with the structural dynamic equation for the motion of the wing is solved. A two-dimensional, elastic and inextensible beam model wing is considered at Re = 1256. The harmonic plunge motion is specified at the leading edge of wing, and the other part of wing is responded passively deforming by the aerodynamic force. By analyzing the flow field, aerodynamic force and energy efficiency of different flexibility wings, it is found that the flexibility influences the aerodynamic characteristics of the plunge wing greatly and when the plunge frequency is less than the structural frequency the flexibility can increase the thrust force and the energy efficiency of the wing, and the maximum energy efficiency is obtained when the wing plunge near the resonance. Moreover, a lighter wing possesses larger energy efficiency than a heavier wing, but it may not be functioning for too light wing. The results obtained in this study will provide physical insight into the understanding of fluid and structure interaction problem.     

尾缘厚度对压气机叶栅气动性能的影响研究

针对不同尾缘厚度对压气机叶栅气动性能影响的问题,采用尾缘对称加厚的方法,在保证弦长、最大厚度、最大厚度相对位置、前缘半径、安装节距和安装角等参数不变的条件下,使尾缘厚度相对于弦长在0.1%~8.0%范围变化。根据Baldwin-Lomax模型建立了压气机叶栅二维湍流流动模型,并对模型近壁面进行了网格加密处理,通过隐式多重网格法加速计算的收敛,利用NUMECA软件,对叶型原型和对称加厚尾缘叶型的总压损失系数、叶型气流转折角和升阻比进行了数值计算。研究结果表明,尾缘厚度在一定范围内增大时,气流转折角减小,升阻比呈先增后降的趋势,而尾缘厚度较大时,推迟了叶型失速的出现,但尾迹损失和总压损失系数较大。     

The effect of the recess shape on performance analysis of the gas-lubricated bearing in optical lithography

Gas-lubricated bearings are widely used in the optical lithographic manufacturing of wafers to realize nearly zero friction for the motion of the stage. As the extreme precise positioning accuracy of these equipments has reached nanometer level, and almost approaches the physical limit, the effect of the recess shape of the gas bearings cannot be neglected any longer. This paper studies the effect of the recessed shape of the bearing on the performance analysis through numerical method. The pressure distribution, as well as the loading capacity and mass flow rate for the case of different shape (no pocketed bearing, rectangular shape and spherical shape bearing, respectively) of the bearing is achieved with the well-known CFD-control element procedures in Quad meshes. The results show that the average loading capacity reduces as the following sequence: rectangular recessed bearing, spherical recessed bearing and non-recessed bearing. The mass flow rate in the bearing with spherical recess is smaller than that of with rectangular recess, and bigger than that of with non-recess. Vortexes, which can cause higher temperature in gas film, are also found in the spherical recess or rectangular recess. It means that only the bearing with non-recess is fitted to use in ultra-high precision equipments.     

Prediction of weld zone shape with effect of tool pin profile in friction stir welding process

Journal of Mechanical Science and Technology - This article investigates the effect of tool pin profile on weld zone shape using computational fluid dynamics techniques in friction stir welding...     

蟹型悬臂梁对光栅平动式光调制器性能的影响

基于MOEMS(Micro-opto-electro-mechanical Systems)的光栅平动式光调制器依靠结构中的蟹型悬臂梁在静电力作用下的上下运动来改变可动光栅和下反射面的距离,从而实现对光能量的调制。本文依据傅里叶光学对光栅平动式光调制器(Grating Moving Light Modulator, GMLM)工作状态的光学特性进行了详细的理论分析和计算机仿真。分析了可动光栅的光栅周期数为偶数和奇数时,由于几何中心的不同,使得采用傅里叶光学分析时透过率函数不同的问题,并对GMLM衍射光能量的分布进行了详细的理论推导;重点讨论了GMLM结构中边框和蟹型悬臂梁对对比度的影响。结果表明,为了得到较高的对比度,应减小边框宽度、悬臂梁的宽度和长度,文章用图形给出了直观说明。     

高速列车头形的设计几何学方法与气动仿真分析

面向国内高速列车外形设计方案推演过程中家族化语言延续性不足,美学性与实用性不匹配,设计概念与设计实施相脱节等问题,运用设计几何学理论中黄金矩形及黄金分割比的设计方法对国内高速列车头形案例进行分析,寻找造型设计的几何比例规律,总结列车头形设计的几何设计框架,形成高速列车头形衍生化方案.运用计算流体力学(CFD)方法时生成...     

Effect of meridional shape on performance of axial-flow fan

In this study, the effect of impeller meridional shape on the performance of axial-flow fan is investigated by CFD method. Three axialflow fan impellers with different meridional shapes are designed. The blade angle, blade stacking condition and other structure factors of the impellers are all remained consistent. The performance curves of the three impellers are calculated and compared. In almost all the interested flowrate range, the impeller W3 with an inverted-isosceles-trapezoid meridional shape and the longer blade camber achieves both the higher pressure rise and the higher efficiency than the other two impellers. A two-stage axial-flow fan designed on basis of W3 is manufactured and tested. Test results show good agreement with the calculated performance curves. Further, analyses of the CFD results are conducted to reveal the reasons for the different performance. A newly-defined Local Euler head (LEH) is introduced to represent the distribution of the major Euler work in the axial-flow fan. And the LEH distributions in the three impellers are obtained. W3 achieves the highest LEH at blade Trailing edge (TE), because it could perform the most Euler work to the fluid with the longest blade camber. Then losses in the impellers are analyzed by means of the entropy generation. Among the losses in impeller, the tip leakage loss and endwall friction loss are dominated at design flowrate. The generation condition of the tip leakage loss shows significant differences among the three impellers. And the whole power loss in impeller of W3 is slightly higher than those of the other two models. However, the power loss difference among the three impellers is negligible. And due to the highest shaft power, the efficiency loss of W3 is the lowest of all.     

对旋轴流风机结构尺寸参数对气动性能的影响

针对FBD No. 8.0矿用对旋轴流风机内部流场不稳定、压力损失较大等问题,对风机内部的集流器和整流罩的几何尺寸参数进行了优化研究。首先,选择集流器入口直径、长度和整流罩的两段水平长度作为正交试验因素,全压效率为试验的评价指标,探究集流器和整流罩的共同作用对风机气动性能的影响;然后,根据L₉（3⁴）的正交试验表,设计了9种试验方案,并进行了数值计算;最后,采用极差分析的方法,得出了几何参数对风机效率的主次影响顺序,确定了对旋轴流风机最优的尺寸参数组合。研究结果表明:相比于原型风机,优化后的对旋轴流风机在流量点750 m³/min时,全压和效率分别提高了2.64%和1.74%;在全流量工况下,全压和效率平均提高了2.12%和2.31%;同时,优化后的风机能够有效缓解入口处的涡团现象,降低风筒前端内部的压力差值,改善进气情况,减小叶片表面的涡量,提高风机的性能。     

叶片后缘加厚对轴流风机性能的影响

为解决NACA65系列翼型叶片后缘轮廓线内切圆半径收敛至0引起的铸造工艺问题,采用三次多项式函数生成叶片后缘厚度函数,精确调整叶片后缘末端厚度.基于Ansys软件对不同叶片后缘厚度的风机进行流体仿真,并分析其气动性能与静力结构特性.结果表明叶片后缘增厚使得叶片附面层分离损失增加,尾迹与叶栅主流区的掺混损失增大.叶片载荷...     

时速400 km高速动车齿轮箱润滑分析

针对时速400 km高速动车齿轮箱润滑设计开展数值仿真研究.首先对时速400 km高速动车齿轮箱总体设计方案中的润滑机理做了简要分析与阐述,明确了数值仿真研究的对象与仿真工况.再对齿轮箱内油浴润滑多相流场特性开展了仿真计算,分析了流场动态特性规律,获得了齿轮箱的润滑特性.最后对所开展的齿轮箱润滑特性研究做出总结,并深入...     

Numerical study on the effect of the tip clearance of a 100 HP axial fan on the aerodynamic performance and unsteady stall characteristics

In this study, a numerical analysis was conducted to investigate the effect of the tip clearance on the aerodynamic performance, internal flow characteristics, and stall region characteristics of an axial fan. Three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes (RANS) calculations were conducted with a shear stress transport (SST) turbulence model. Tip clearance ratios of 0, 0.01, and 0.02 were applied to the impeller. As the tip clearance ratio increased, the aerodynamic performance of the axial fan decreased at both the design and the off-design conditions. The correlation between the tip leakage vortex (TLV) and the flow angle of the velocity triangle was presented for the difference in the tip clearance and flow rate. As the flow rate increased, the differences in the aerodynamic performance induced by the tip clearance ratio decreased. As the tip clearance ratio increased, the size of the TLV increased and gradually moved in the circumferential direction to interfere with the main flow at the low flow rate. Meanwhile, the size of the TLV was similar and gradually moved in the axial direction even if the tip clearance ratio increased at the high flow rate. The pressure fluctuations were observed by the fast Fourier transformation (FFT) analysis to compare and analyze internal flow characteristics at the stall region and design point. The static pressure was converted to the appropriate magnitude. The locations of the highest magnitude were shown to be different at the stall region and the design point, respectively.