Effect of Sweptback Angle of a Delta Wing on Surface Pressure Distribution at Supersonic Mach Numbers

The purpose of this work is to shed light on the effect of the pivot position on the surface pressure distribution over a 3D wing in different flight conditions.The study is intended to support the design and development of aerospace vehicles where stability analysis,performance optimization,and aircraft design are of primary importance.The following parameters are considered:Mach numbers(M)of 1.3,1.8,2.3,2.8,3.3,and 3.8,angle of incidence(θ)in the range from 5°to 25°,pivot position from h=0.2 to 1.The results of the CFD numerical simulations match available analytical data,thereby providing evidence for the reliability of the used approach.The findings provide valuable insights into the relationship between the surface pressure distribution,the Mach number and the angle of incidence.

Effect of Turning Angle on Flow Field Performance of Linear Bowed Stator in Compressor at Low Mach Number

A comparison of the results of a computational simulation and an experimental measurement indicates a good agreement between them： the bowed blade lowers the energy loss coefficient of engine by 11% in the simulation and by 13% in the measurement. To further discuss the application conditions of bowed blade in compressor, with incidence equal to zero and other boundary conditions unchanged, a computational investigations on four series of linear stators with different aerofoil turning angles are achieved. It is found that the bowed blade has much positive effect in high airfoil turning angle cascade, for example, the optimal retrofit of 30° bow angle highly reduces the energy loss coefficient by 17.9%, when the aerofoil turning angle is 59.5 °. But the optimal retrofit of 15° has only 0.7% reduction when the aerofoil turning angle is 39.5°, or even the compressor performance will get worse with the bow angle gradually increasing. Consequently, it is verified that the turning angle is one of the important factors to decide whether to apply the bowed blade into compressor at low Math number.

Determination of rice panicle numbers during heading by multi-angle imaging

Plant phenomics has the potential to accelerate progress in understanding gene functions and environmental responses. Progress has been made in automating high-throughput plant phenotyping. However, few studies have investigated automated rice panicle counting. This paper describes a novel method for automatically and nonintrusively determining rice panicle numbers during the full heading stage by analyzing color images of rice plants taken from multiple angles. Pot-grown rice plants were transferred via an industrial conveyer to an imaging chamber. Color images from different angles were automatically acquired as a turntable rotated the plant. The images were then analyzed and the panicle number of each plant was determined. The image analysis pipeline consisted of extracting the i2 plane from the original color image, segmenting the image, discriminating the panicles from the rest of the plant using an artificial neural network, and calculating the panicle number in the current image. The panicle number of the plant was taken as the maximum of the panicle numbers extracted from all 12 multi-angle images. A total of 105 rice plants during the full heading stage were examined to test the performance of the method. The mean absolute error of the manual and automatic count was 0.5, with 95.3% of the plants yielding absolute errors within ± 1. The method will be useful for evaluating rice panicles and will serve as an important supplementary method for high-throughput rice phenotyping.

Collisional Quantum Interference on Rotational Energy Transfer： Relation Between Integral Interference Angle and Rotational Quantum Number in Na2（A^1∑u^＋,ν=8～b^3∏0u,ν=14）-Na System

Collisional quantum interference （CQI） on rotational energy transfer was observed in Na2（A^1∑u^＋,ν=8～b^3∏0u,ν=14） system in collision with Na [Chem. Phys. Lett. 318 （2000） 107], and the degree of the interference was measured. The integral interference angle was obtaJned through theoretical calculation. We will research the factors that have effect on collisional quantum interference on rotational energy transfer in Na2（A^1∑u^＋,ν=8～b^3∏0u,ν=14）-Na system. Basing on the time-dependent first order Born approximation, and taking into account the anlsotroplc Lennard Jones interaction potentials and ＂straight-line＂ trajectory approximation, we obtain the factors that have effect on CQI in Na2-Na system, and obtain the relation between the integral interference angle and rotational quantum number.

Influences of attack angle and mach number on aerodynamic characters of typical sections of extra-long blade in a steam turbine

On super-sonic or trans-sonic planar cascade wind tunnel of free jet intermittent type, wind blowing experiments were performed on the typical sections of stator and rotor blades in the last stage of ultra-ultra-critical steam turbine with extra-long blade of 1200mm. The influences of attack angle and Mach number on the aerodynamic performances of these sections of the blade profiles were verified, and their operating ranges were also specified.

Modified smoothed particle hydrodynamics approach for modelling dynamic contact angle hysteresis

Dynamic wetting plays an important role in the physics of multiphase flow, and has a significant influence on many industrial and geotechnical applications. In this work, a modified smoothed particle hydrodynamics (SPH) model is employed to simulate surface tension, contact angle and dynamic wetting effects at meso-scale. The wetting and dewetting phenomena are simulated in a capillary tube, where the liquid particles are raised or withdrawn by a shifting substrate. The SPH model is modified by introducing a newly developed viscous force formulation at the liquid-solid interface to reproduce the rate-dependent behaviour of the moving contact line. Dynamic contact angle simulations with the interfacial viscous force are conducted to verify the effectiveness and accuracy of this new formulation. In addition, the influence of interfacial viscous forces with different magnitude on the contact angle dynamics is examined by empirical power-law correlations;the derived constants suggest that the dynamic contact angle changes monotonically with the interfacial viscous force. The simulation results are consistent with experimental observations and theoretical predictions, implying that the interfacial viscous force can be associated with the slip length of flow and the microscopic surface roughness. This work demonstrates that the modified SPH model can successfully account for the rate-dependent effects of a moving contact line, and can be used for realistic multiphase flow simulations under dynamic conditions.

Roll angle measurement system based on triaxial magneto-resistive sensor

Aiming at large error when inertial devices measure the roll angle under high overload conditions,the article designs one kind of roll angle measurement system based on magneto-resistive sensor which calculates the roll angle by micro controller STM32.Experiment results of a triaxial turntable show that using magneto-resistive sensor to measure roll angle is feasible and of high accuracy,and it can calculate the roll angle of the conventional projectile with the error in 1°.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

Entanglement Enhancement in an XY Spin Chain

We study evolution of entanglement in an XY-type spin channel and find that the entanglement can be enhanced by the spin channel.The parameter regions of the initial states for different numbers of sites are obtained.Furthermore,we consider a common spin environment coupling to the spin chains and find that the entanglement enhancement can also be implemented only for the chains with the odd numbers of sites.

Experimental Study and 3D CFD Analysis on the Optimization of Throttle Angle for a Convergent Vortex Tube

Seven adjustments of convergent-type Vortex Tube （VT） with different throttle angles were applied. The adjustments were made to analyze the influences of such angles on cold and hot temperature drops as well as flow structures inside the VTs. An experimental setup was designed, and tests were performed on different convergent VT configurations at injection pressures ranging from 0.45 to 0.65 MPa. The angles of the throttle valve were arranged between 30° to 90°, and the numbers of injection nozzles ranged between 2 and 6. Laboratory results indicated that the maximum hot and cold temperature drops ranged from 23.24 to 35 K and from 22.87 to 32.88 K, respectively, at four injection nozzles. Results also showed that temperature drop is a function of hot throttle valve angle with the maximum hot and cold temperature drops depending on the angle applied. We used graphs to demonstrate the changes in the cold and hot temperature drops with respect to hot throttle angle values. These values were interpreted and evaluated to determine the optimum angle, which was 60°. The CFD outputs agreed very well with the laboratory results. The proposed CFD results can help future researchers gain good insights into the complicated separation process taking place inside the VTs.

The Significance of Solutions Obtained from Ill-Posed Systems of Linear Equations Constituted by Synchrotron Radiation Based Anomalous Small-Angle X-Ray Scattering

Synchrotron radiation based experimental techniques known as Anomalous Small-Angle X-ray Scattering (ASAXS) provide deep insight into the nanostructure of uncountable material systems in condensed matter research i.e. solid state physics, chemistry, engineering and life sciences thereby rendering the origin of the macroscopic functionalization of the various materials via correlation to its structural architecture on a nanometer length scale. The techniques constitute a system of linear equations, which can be treated by matrix theory. The study aims to analyze the significance of the solutions of the stated matrix equations by use of the so-called condition numbers first introduced by A. Turing, J. von Neumann and H. Goldstine. Special attention was given for the comparison with direct methods i.e. the Gaussian elimination method. The mathematical roots of ill-posed ASAXS equations preventing matrix inversion have been identified. In the framework of the theory of von Neumann and Goldstine the inversion of certain matrices constituted by ASAXS gradually becomes impossible caused by non-definiteness. In Turing’s theory which starts from more general prerequisites, the principal minors of the same matrices approach singularity thereby imposing large errors on inversion. In conclusion both theories recommend for extremely ill-posed ASAXS problems avoiding inversion and the use of direct methods for instance Gaussian elimination.

不等大液滴在不同润湿性壁面碰撞聚结过程实验研究

在工业生产过程中,液滴碰撞的控制和利用对于涂覆、喷涂、沉积等工艺有着重要意义。为了分析不等大液滴在不同湿润性壁面碰撞聚结的过程,制备了体积比为12的不等大液滴,利用高速摄像技术,开展了不同润湿性基板上小液滴撞击大液滴的碰撞实验,对液滴碰撞聚结动力学行为进行分析。实验结果表明,在韦伯数为8.07≤We≤40.38与基板接触角α=100°、120°、145°、160°的实验范围内,液滴出现反弹聚结和接触聚结两种现象。双液滴碰撞聚结后,液滴的最大铺展直径与韦伯数呈正相关,与基板接触角呈负相关。最大射流高度随韦伯数增加先升高后降低,随接触角增加而增加。实验范围中,双液滴碰撞聚结过程中最大铺展直径为d_(p,max)=8.41 mm,最大射流高度h_(s,max)=6.92 mm。

T型微通道入口角度对剪切变稀流体微液滴制备影响

为了研究T型微通道入口角度对非牛顿微液滴制备影响,采用流体体积(VOF)模型对聚丙烯酰胺水溶液微液滴形成过程进行数值模拟,开展高速数码显微实验对数值模拟结果进行验证。结果表明:在相同工况条件下,非牛顿微液滴生成频率随着分散相入口角度的增大呈先增大后减小的趋势,相对长度呈现先减小后增大的趋势。在入口角度小于90°时,随着入口角度的增加,微通道内两相平均压差、液滴断裂时刻两相压差最低值随之升高,在入口角度大于90°时,上述压差则随着入口角度的增加而降低。考虑两相体积流量比与连续相毛细数并引入关于分散相入口角度的修正系数,提出聚丙烯酰胺水溶液微液滴相对长度预测公式,为剪切变稀流体微液滴制备提供参考。

几何参数对轮缘推进器水动力性能影响的研究

轮缘推进器是近年来发展起来的一种无轴组合式特种推进器。与传统推进器相比,轮缘推进器在水动力设计和性能分析方面存在诸多挑战,水动力性能的研究对轮缘推力器的设计和应用具有重要意义。为了研究几何参数对轮缘推力器水动力性能的影响,本文以7叶轮缘驱动推力器为基本模型,基于面元法原理,利用编译的面元法代码对轮缘推力器在开阔水域的工作状态进行了数值模拟。通过求解每个面元的速度场,计算了水动力性能和叶片表面压力分布。此外,本文选择了几个典型的几何特征,如螺距比和叶片数,通过进行变参数分析,比较了不同几何参数下轮缘推力器的敞水性能。结果表明:本文的相关研究对轮缘推力器的设计和开发具有参考价值。

横向冲击载荷下齿形双螺母防松性能

针对螺栓连接结构在舰船爆炸冲击中容易发生松动的现象,设计了一种齿形双螺母的防松结构。利用局部滑移理论分析齿形双螺母的防松原理,采用有限元仿真法,通过预紧力和微滑移的变化量对其防松性能进行分析,并研究了齿形双螺母防松性能的影响因素及其影响规律。研究结果表明:横向冲击载荷下,齿形双螺母预紧力下降慢,微滑移变化小,具有较好的防松性能;当楔形角与螺纹升角相同时,防松效果最差;楔形角越大,齿形数量越多,齿形双螺母的防松效果越好。

背压扰动平衡盘对涡旋压缩机黏性内流压力影响研究

在变转速工况下,电动涡旋压缩机背压腔中润滑油产生的背压力无法准确平衡轴向气体力。针对这一问题,提出了一种带有扰动片的背压扰动平衡盘,研究了背压扰动平衡盘对涡旋压缩机黏性内流压力的影响。首先,对背压扰动平衡盘作用原理进行了分析,使用贝塞尔曲线构建了扰动片型线,对润滑油被扰动后的静压增量进行了公式推导,计算了扰动片出口安装角和扰动片数对润滑油静压的影响;然后,建立了含背压扰动平衡盘的背压腔模型,将流体域分为旋转域和静止域,采用旋转坐标系的方法进行了数值模拟,研究了背压腔内润滑油的压力场;最后,根据理论计算,模拟了润滑油在不同出口安装角和扰动片数下的润滑油静压,对润滑油静压与压缩机所需最佳背压进行了对比分析。研究结果表明:采用背压扰动平衡盘可以使润滑油静压增加21%,且静压增量随主轴转速的增加而增大,适当增大扰动片出口安装角可使润滑油静压增加0.032 MPa;对比最佳背压可知,扰动前润滑油静压与最佳背压相差26%,而合理设计扰动片后的润滑油静压与最佳背压相差仅为9%,极大改善了电动涡旋压缩机在变转速下的轴向平衡。

植被弯曲形态对水流的阻力效应研究

植被化生态河道的阻力特性是环境水力学的研究热点之一。为探寻柔性植被不同弯曲倾角下的阻力特性,利用圆柱铝棒进行弯曲模拟柔性植被,并采用测力装置,对不同倾角状态下圆柱铝棒及流速范围开展室内水槽试验,首先研究直立圆柱铝棒阻力与流速之间的关系,得到的拖曳力系数Cd符合已有研究,同时验证了测力装置的可靠性;随后开展不同倾角下的植被阻力试验,得到Vogel数随着倾角的减小呈逐渐降低最后突增的趋势。当植被弯曲时,已有的刚性直立植被丛模型不再适用,通过引入与倾角相关参数Cθ对模型进行修正,显著提高了模拟精准度。研究结果可为生态植被化河道水力学精准模拟提供技术支撑。

超声速边界层自然转捩影响因素研究

为了研究马赫数、雷诺数、后掠角、壁面温度和压力梯度等因素对超声速边界层自然转捩横流模态和Oblique T-S模态的影响,在平板、翼型和无限展长后掠翼等二维或准三维流动中使用线性稳定性理论(LST,linear stability theory)和eN转捩预测方法,通过变参数分析研究了这几类影响因素分别对横流模态和Oblique T-S模态N因子的作用效果。基于文中算例所设置的来流和壁面条件进行计算,计算结果表明,横流模态N因子增长速率分别与来流马赫数、雷诺数呈正相关;随着后掠角从30°增加到60°,横流模态N因子值的增长不断加快,超过60°以后驻波N因子值增长开始减弱,而行波N因子值在60°~75°范围内变化不明显,可以推断行波N因子值开始衰减的临界后掠角更大;Oblique T-S模态N因子值的增长速率分别与来流雷诺数、壁面温度与来流温度的比值呈正相关,当来流马赫数越大或者顺压力梯度越大时增长速率减小。因此,来流马赫数的变化对自然转捩的影响与所分析的不稳定模态类型有关,而来流雷诺数的变化对自然转捩横流模态和Oblique T-S模态N因子的影响趋势是一致的。

估计混响室旋转搅拌器相关角度的快速方法

为保证混响室中样本的统计独立性,混响室内搅拌器的相关角度给出了测试过程中搅拌器步进角度的下界。依照IEC 61000-4-21:2011确定搅拌器相关角度时,由于每次转动角度较小,完整旋转一周所需时间较长。为缩短测试时间,提高测试效率,提出一种快速评估相关角度的方法,即使搅拌器不完成整周旋转,相关角度也可以准确估计,从而大幅度减少测试时间。测试结果对不同旋转角度进行了比较,与完整旋转一周的结果吻合良好,证实了文章方法的有效性。

叶片结构参数对涡流分级机分级性能的影响

为了探究叶片安装角度与叶片数量对涡流分级机分级性能的影响,对6种不同叶片结构的分级轮进行了数值模拟研究。制备了4种不同叶片结构的分级轮分别加工金属硅、碳酸钙和碳素,并得出各个物料的分割粒径、分级精度作为评价涡流分级机性能的指标。结果表明:可通过增加叶片数量与偏移叶片安装角度,达到对环形分级区内外流场的优化效果以保证物料分级的顺利进行。叶片安装角度由15°提升至60°、叶片数量由72片降至48片后,金属硅、碳酸钙和碳素切割尺寸分别由2.45 m、1.679 m和2.822 m降低至2.147 m、1.427 m和1.816 m;金属硅、碳酸钙和碳素的分级精度分别由37.44%、40.48%和40.94%变化至38.58%、40.38%和45.00%。叶片安装角度变化对分级性能影响更为显著。