Aerodynamic topology optimization on tip configurations of turbine blades

Journal of Mechanical Science and Technology - The topology optimization (TopOpt) is adopted in this article to design tip geometries of a turbine blade. Its principle is to modify the porosity,...     

空气动力套件对汽车气动性能影响的研究

随着计算机技术不断地高速发展,在越来越多的汽车以及车身附件的开发设计过程中运用了计算流体力学(CFD)方法。以计算流体力学为理论基础,以简化处理后的某型SUV模型作为研究对象,以CATIA、ICEM-CFD以及ANSYS-FLUENT作为研究工具对汽车的气动性能进行研究。通过仿真计算得到了原始模型和三种加装气动套件模型的车身阻力系数和升力系数。综合动力性、经济性、稳定性对计算结果进行对比,分析了加装不同气动套件汽车的气动性能差异以及产生这些差异的主要原因,并根据不同需求选出合适的加装方案。     

Tip gap flow and aerodynamic loss generation in a turbine cascade equipped with suction-side winglets

The tip gap flow and aerodynamic loss generation over a plane tip equipped with a “constant-width suction-side” (CWSS) winglet and a “varying-width suction-side” (VWSS) winglet have been investigated in a turbine cascade. For a fixed tip gap of h/c = 2.0%, three different winglet widths of w/p = 5.28, 10.55, and 15.83% are tested for the CWSS winglet. The VWSS winglet is designed based on flow visualization and has almost the same winglet area as the CWSS winglet of w/p = 15.83%. In general, the suction-side winglets have a role to increase aerodynamic loss in the tip leakage vortex region but reduce aerodynamic loss in the passage vortex region. For the CWSS winglet, the total-pressure loss coefficient mass-averaged all over the measurement plane has no appreciable changes with increasing w/p from 0.0 to 10.55%, but tends to decrease with further increment of w/p. The VWSS winglet performs better in reducing aerodynamic loss in the passage vortex region than the CWSS winglet of w/p = 15.83% but leads to a little bit higher aerodynamic loss in the tip leakage vortex region. The aerodynamic loss reduction by the VWSS winglet is 7.4% in comparison with the plane tip without winglet, and is about 60% lower than that by the widest CWSS winglet.     

微型扑翼飞行机器人气动力测试系统

微型扑翼飞行机器人飞行时的气动力是主要的性能指标,低雷诺数下的空气动力学还没有成熟的理论和经验公式可以遵循,因此需要设计并验证了一个微型扑翼飞行机器人气动力测试系统:采用2个位于水平和垂直方向的力传感器作为敏感元件分别测量微型扑翼飞行机器人飞行时的推力和升力,使用两个柔性铰链分离垂直、水平方向的气动力,降低非测力方向力对力传感器的影响。文末给出并分析了该系统用于微型扑翼飞行机器人气动力测试的实测推力和升力。     

A heater-integrated scanning probe microscopy probe array with different tip radii for study of micro-nanosize effects on silicon-tip/polymer-film friction

Electric-heated cantilever-tip probes fabricated by micromachining techniques can be used for high-density data storage, nanopatterning, etc., where contact-scanning and thermal-plastic nanowritings are frequently implemented on the surface of a polymer thin-film such as polymethylmethacrylate (PMMA). In such kind of applications, micro-nanofriction effects, e.g., contacting-size and temperature effects of the tip/film friction system, will largely influence the performance of the applications. To elucidate the effects, present research fabricates a monolithically integrated probe array that comprises three scanning probe microscopy cantilever-tip probes with different tip radii of tens of nanometers, submicrometers and microns, respectively. The tip is enabled an electric-heating function by integrating a heating resistors on the tip. Using the tips, the tip/film friction experiment shows an obvious contacting-area effect. Within a wide temperature range, the friction signal and the normal force load exhibit a nonlinear relationship for the nanoradius tip but a linear relationship for the submicron tip. With the heated tips, the experiment directly reveals significant size effects on friction and adhesion behaviors. It is found that the glassy transition of the PMMA film can be characterized using the submicron tip, while the nanotip is suited to detect the secondary beta transition process. By fitting the experimental data into a power law with apparent friction coefficient included, the temperature-effect combined size effect of the micronano tip/polymer friction is modeled and discussed.     

具有组合式叶片的导流型垂直轴风力机气动性能的数值研究

在分析传统垂直轴风力机低效率原因的基础上阐述导流型垂直轴风力机的结构优势,并提出一种带组合式叶片的导流型垂直轴风力机,同时数值研究该垂直轴风力机的气动特性.这种垂直轴风力机由导风轮与风轮构成,其中导流叶片分别由进口径向段、出口导流段,以及与两者相切的中间圆弧段等三段组合而成,风叶是由进口圆弧段及与之相切的出口直线段组合而成.导流叶片不仅可以有效地降低因来流对风叶吸力面的直接冲击而造成的阻力转矩,而且还有助于增强来流对风叶压力面的有效冲击.这两方面均有助于使该种风力机风轮的旋转转矩得到显著增加.研究结果表明:这种带有组合式叶片导流型垂直轴风力机,具有工作范围宽、最佳尖速比大、风能利用率高等特点,其气动性能在数值上已明显超过常规垂直轴风力机的一般水平.在此基础上,将机翼型叶片引入导流型垂直轴风力机中,并数值论证了即使在这种变攻角、剧烈分离的垂直轴风力机的内部流场中,机翼型叶片对整个风力机性能的提高也能起到一定的作用.这种带有组合式叶片的导流型垂直轴风力机不仅具有较好的气动性能,而且具有简单的二维外形结构便于加工,具有推广使用的潜力.     

V-shaped metal-oxide-semiconductor transistor probe with nano tip for surface electric properties

We design and fabricate a V-shaped metal-oxide-semiconductor (MOS) transistor probe with the focused-ion-beam (FIB) nano tip to measure surface electric properties. The V-shaped structure is selected for its better lateral stiffness, and the specific dimensions are determined using the parallel beam approximation (PBA). The deposition conditions for the nano tip are also investigated for better tip sharpness. The high working frequency of the MOS transistor improves the scanning speed and the high sensitivity reduces the additional equipment required. The detection properties of the device are investigated with PZT poling patterns. The measured results show well-defined patterns, promising that the device can detect surface electric properties with high sensitivity and high working frequency.     

基于不同井道模型的超高速电梯气动特性研究

针对超高速电梯气动特性研究问题,对比研究了电梯运行10 m/s时二维井道模型、三维井道模型及带层门地坎的三维井道模型。利用ANSYS有限元软件对各模型下的井道气动特性进行了分析,研究得到了各井道模型中不同截面上的气流分布情况,并进行了比较研究;建立了井道对称截面上各直线位置处气流的速度特性曲线,对井道前后侧速度大小进行了研究;建立了对称截面各直线上气流最大值,并进行了比较分析;在两种不同的三维井道模型中,针对层门地坎对轿厢的气动力影响大小进行了分析。研究结果表明,二维井道模型中整体井道流速大,最大流速相比增大近25%,且无法捕捉井道左右侧气流影响;三维井道模型中,层门地坎导致井道后侧流速增大,井道前侧流速减少,同时增加轿厢上下气动阻力93.2%及轿厢前后倾覆力566.7%。     

Vortex dynamic characteristics of unsteady tip clearance cavitation in a waterjet pump determined with different vortex identification methods

Journal of Mechanical Science and Technology - The cavitating flow field in waterjet pumps is complex, especially tip leakage cavitation (TLC), which has been a puzzle to researchers for decades....     

透平叶栅自动气动优化设计方法

为提高叶栅的气动性能,提出基于能量法的叶栅自动设计参数化方法,结合自适应差分进化算法和Reynolds-Averaged Navier-Stokes (RANS)方程求解技术,提出适用于透平叶栅气动优化设计的自动气动优化算法。以总压恢复系数最高为目标函数,在满足流量和出口气流角约束条件下,利用提出的气动优化算法对一小展弦比后加载叶栅进行了自动气动优化设计。优化后,叶栅的总压恢复系数提高了0.7%,叶栅的气动性能明显提高。优化结果表明该算法具有良好的优化性能和应用前景。     

车辆仿生结构气动特性分析与优化

以Ahmed车辆为研究对象,采用CFD数值模拟的方法,研究非光滑棱纹仿生结构对车辆空气动力学特性的影响。对不同行驶速度下原车尾涡速度矢量分布以及升阻力系数的仿真计算,并根据风洞试验结果验证数值模拟的有效性。在原车尾部设计非光滑棱纹仿生结构,以阻力系数和升力系数为优化设计目标函数,以仿生结构的几何尺寸,空间布置尺寸,以及行驶车速作为设计变量,建立Kriging近似模型,并采用多目标遗传算法进行带有棱纹仿生结构的Ahmed车辆模型优化分析。经CFD验证,优化后的带有棱纹仿生结构的Ahmed车辆模型阻力系数降幅约为5%,升力系数降幅约为29.35%,能够起到显著的减阻增稳效果。计算结果也表明,建立的Kriging近似模型的误差为2%左右,可信度较高。     

微型轴流风扇气动相似特性研究

微型轴流风扇是计算机等电子设备的重要散热部件,当前随着计算机尺寸变小而运算速度的提高,其发热量也随之增加,这对微型轴流风扇的气动设计提出更高的要求。相似设计作为一种重要而有效的设计方法,已广泛运用于大中型风扇的气动设计中,但其在微型轴流风扇的应用尚未广泛开展,其主要原因是微型轴流风扇内部的流动位于Re数非自模区,用于大中型风扇相似设计中的行之有效的设计方法在微型轴流风扇的设计中达不到应有的效果。基于此,利用气体动力学相似原理,推导微型轴流风扇气动相似所须满足的条件,并与流动位于Re数自模区的大中型轴流风扇的气动相似规律相对比,提出使微型风扇实现气动相似的"弦长雷诺数"准则,并数值验证该准则对微型轴流风扇气动相似的有效性,同时分析该准则的适用条件与局限性。研究结果表明,"弦长雷诺数"准则能较好地实现微型轴流风扇的气动相似,但其要求模型叶轮与原型叶轮转速之比与其几何缩小的比例尺的平方成正比。这就要求模型叶轮的缩小比例不能过大,否则不仅易导致其所须转速过大而实际无法实现,而且会导致由于离心力的差别过大而使其气动性能的相似性出现偏差。     

Aerodynamic performance analysis of partial admission dual row control stage at different working conditions

Aerodynamic performance of partial admission dual row control stage at the rated and off-designed operating conditions was numerically investigated using three-dimensional Reynolds-averaged Navier-Stokes (RANS) and k -ε turbulence model. The full scale computational model includes the four nozzle boxes, full first and second row rotor blade, as well as two admission guided vanes with consideration of the rotor tip clearance and stator diaphragm gland. The numerical results of the mass flow rate, power output and aerodynamic efficiency of the dual row control stage at the rated and off-designed conditions are well in agreement with the experimental data. The obtained results at rated condition show that the blocking segmental arc of guided vane increased the exit pressure of the upstream nozzle, which reduced the mass flow rate and changed the aerodynamic performance of the nozzle. The circumferential non-uniformity of aerodynamic parameters and partial admission losses increases with the decrease in the admission degree for the computed three operating conditions. The analysis of axial steam velocity shows that the trailing shedding vortex and the complex flow vortex in flow passages have a significant impact on the magnitude and direction of the axial steam velocity. Furthermore, the partial admission degree changed the proportions of the power output of two rotor blade rows. The lower partial admission degree leads to a larger proportion of the power output of the first rotating blade row. The detailed flow pattern in the partial admissions dual row control stage at different operating conditions is also illustrated.     

点焊机电极的修磨器设计

针对点焊机电极磨损造成电极端面面积增加,电极磨损严重时影响焊接质量的问题,设计了可调速立式电极修磨器。通过对电极修磨器的设计原理分析和结构设计,证明该设计具有修磨精度高,应用范围广的特点,可广泛适用于点焊机领域,及汽车业焊接生产线的点焊机领域。     

圆角方形断面气动特性试验

通过刚性测压模型风洞试验,在均匀流场中测试了圆角率R/D=0.4的方形断面在0°～45°风向角、雷诺数Re=0.8×10~5～3.8×10~5时的气动特性。结果表明:试验雷诺数范围内,所有风向角下模型的阻力系数均值、升力系数均值、升力系数脉动值及斯特罗哈数基本上都受到雷诺数的影响。与其他风向角相比,0°～17.5°风向角时,阻力系数均值和升力系数均值受雷诺数的影响更大; 7.5°～45°风向角时,升力系数脉动值受雷诺数的影响更大; 0°～12.5°风向角时,斯特罗哈数受雷诺数的影响更大。     

Power losses at low speed in a gearbox lubricated with wind turbine gear oils with special focus on churning losses

In this study gear oils were tested for power loss behaviour in a two stage multiplying gearbox, on a back-to-back test rig with recirculating power. The tests were performed at low input speeds and high input torques with oil sump temperature set free.A power loss model simulating the power loss mechanisms was implemented to evaluate gear power losses, but failed to correctly describe the gear churning.Two lubricant flow regimes were identified, which are related to the nature of the fluid circulation, as well as with the gearbox case. A calibration method for the gear churning loss is proposed based on these results and a method to identify the transition between the fluid flow regimes inside the gearbox.     

考虑附加质量的中心刚体-柔性悬臂梁系统的动力特性研究

对考虑附加质量的中心刚体-柔性悬臂梁系统的动力特性进行研究.首先采用Hamilton原理和有限元离散化方法,在计入柔性梁由于横向变形而引起的轴向变形的二阶耦合量的条件下,给出该系统的刚柔耦合动力学方程(即一次近似耦合模型),以及相应的非惯性系下的动力学模型,然后通过数值仿真对系统的动力特性进行研究.仿真结果显示,即使是小的附加质量也会对系统动力特性产生重要影响,附加质量使得梁的响应幅值变大和响应频率降低,且会影响柔性梁和中心刚体的终点位置.附加质量的影响随系统大范围运动的角速度的增大而变大.当系统大范围运动为低速时,传统的混合坐标模型仍然会导致较大误差;当系统大范围运动为高速时,传统的混合坐标模型存在失效的可能.     

Weldability of titanium and nickel with alloy filler addition and different electrodes tip shapes by using micro spot brazing method

The weldability of titanium and nickel using micro spot brazing technology was successfully investigated. Brazing was performed using a 4-kA welding current, 2-V voltage, 60-N load, and a 25–50-ms welding time. An alloy filler metal, specifically a 0.1-mm thick foil with a composition of 71Ag-28Cu-1Mg, was sandwiched between Ti and Ni. The three electrode copper tip shapes that were investigated in this study were circular-, rectangular-, and ring-shaped tips. The weldability of the joint was evaluated in terms of the fracture load, weld size, shear strength, and micro hardness. A high joint strength was obtained in the case of the 71Ag-28Cu-1Mg filler when a rectangular electrode tip face was used.     

涡轮叶片三维气动优化设计

根据五次多项式叶片造型方法进行叶型参数化，得到涡轮叶片的参数化模型，采用N—S方程进行三维流场计算，使用模拟退火算法和序列二次规划算法相结合，以涡轮气动效率为目标进行了优化，优化结果显示涡轮气动效率得到提高。算例表明文中涡轮叶片参数化方法是可靠的，文中提出的叶片三维气动性能优化方法是可行的。