齿轮范成法计算机辅助教学的实现

一、引言 渐开线齿轮的范成法加工长期以来一直是机械设计课程教学中的重点和难点。为加深学生对这部分概念的理解,在教学中特意安排了2至3个小时的实验,但由于受实验仪器——齿轮范成仪和实验时间的限制,只能作出模数为20、压力角为20°、齿数为10的标准齿轮和变位齿轮的二至三个齿形（其中只有一个齿形是完整的）,并且还无法图示说明模数、压力角、齿数变化时齿轮几何尺寸、齿形、基圆半径与齿根圆半径的相对位置的变化情况。利用计算机的特长进行齿轮范成法的教学,可较好地解决以上的问题,并且在齿轮参数的选择上也没有限制。     

跨声压气机转子进口总压畸变的数值仿真

研究燃气涡发动机问题,进气畸变会严重影响压气机的稳定性,针对目前对进气畸变问题研究的不足,为提高工作稳定性,利用全三维定常数值仿真方法研究了一跨声压气机转子在不同类型的稳态总压畸变入口条件下的特性,并对比分析了三种典型转速工况下稳态周向总压进气畸变对压气机转子的影响并进行仿真.仿真结果表明,在设计转速,相同进气畸变强度下,径向叶尖畸变时转子的性能和稳定性的降低最大,而径向轮毂畸变时转子的稳定裕度有所提高,证明系统的性能得到改善.     

双转子涡喷发动机气动性能优化控制研究

航空发动机的控制规律作用巨大,它决定了发动机能否获得设定的稳态工作下性能指标,同时保证工作过程中的压气机和涡轮的气动稳定性;双转子涡喷发动机气动性能优化控制的目的就是有效地挖掘发动机的使用潜力;研究方法采用部件特性法对发动机进行稳态建模,并针对某双转子涡喷发动机的稳态模型进行三种不同稳态控制规律下的仿真,得到发动机性能参数的不同变化趋势,并对其进行了详细的分析;结果表明:保持低压转子转速不变的情况下,随着压气机进口总温的增加,高压转子转速上升,涡轮前温度升高,发动机推力增加;保持涡轮前温度不变的情况下,随着压气机进口总温的升高,低压压气机气动负荷变重,低压转子转速降低;高压转子转速也下降,但是下降幅度很小;燃油流量增加;保持高压转子转速不变的情况下,随着压气机进口总温的升高,燃油流量有一定的增加,低压转子转速有所降低;推力受多重因素的影响,推力值变化趋势较为复杂。     

16V265H型增压柴油机涡轮设计与仿真分析

新型大功率内燃机车以其高效、节能、环保的优良性能而被广泛使用。涡轮作为其核心部件,它的性能对铁路运能有着重要的意义。根据开发的增压系统热力参数估算和轴流涡轮一维设计程序,完成了16V265H型增压柴油机轴流涡轮的设计,从结果看出,模拟出的质量流量高于设计要求0.22%,而总静效率约高于设计要求2.4%;并通过三维数值模拟研究了叶轮基础流场和变工况性能分析,可以看出设计的涡轮在不同的工况下气动性能良好;在以上研究的基础上分析了叶片厚度分布和前缘半径对涡轮性能的影响,在设计工况下,不同叶片厚度分布和不同前缘半径对涡轮性能有一定的影响,只通过改变叶型厚度和前缘半径可以在一定程度上改善叶片载荷分布。     

CAE软件操作小百科(26)

1如何在CATIA V5中绘制斜齿圆柱齿轮和直齿圆柱齿轮?斜齿轮因具有特殊的几何特征和啮合方式,可提高传动的稳定性,在高速大功率传动中得到广泛应用.在CATIA V5中绘制斜齿轮的步骤如下.1)在公式f(x)中输入齿轮的各项参数及其相互关系,包括齿数、模数、压力角、齿顶圆半径、分度圆半径、齿根圆半径、基圆半径、螺旋角和齿厚等.2)画出齿轮齿根圆柱.3)通过法则曲线fog建立一组参数函数,利用     

重物撞击圆板时的冲击力计算研究

研究了重物对圆板的冲击问题．采用伽辽金原理及拉普拉斯变换推导出了物体对圆板的冲击力解析表达式．通过数值实例,讨论了圆板半径、板厚、缓冲垫刚度、重物下落高度、重物质量等因素对重物对圆板冲击力影响,并绘出了冲击力随时间的变化曲线．算例表明：用该法求冲击力问题,不但比传统的Hertz接触理论更接近真实情况,而且计算简便,便于工程设计人员应用．     

相交轴转子系统当量化建模与扭振响应分析

齿轮联结的相交轴转子系统具有转子不同体、不同速、不同轴线等结构特点,使其动力学建模异于常规转子系统,论文采用当量化建模方法,将相交轴转子系统转化为同转速、同轴线的转子系统并建立动力学模型,通过与已有研究对比验证了文中基于DyRoBeS当量化建模方法的有效性.以相交轴齿轮联结转子系统典型结构——某型直升机尾传动系统为研究对象,建立了当量化转子系统动力学模型,分析了系统各阶扭振临界转速及其组成、联结齿轮啮合刚度对扭振的影响、联结齿轮转动惯量对系统临界转速的影响,结果表明:传动系统第1、2阶临界转速为派生临界转速,其余8阶均源于各组成轴;中、尾减啮合刚度值与扭振的各阶共振峰值存在映射关系,部分啮合刚度值会激发共振极大值,应尽量避免;中、尾减啮合刚度变化会引发系统临界转速的变化,尤其是第1、2阶临界转速;不同阶临界转速对各个联结齿轮转动惯量的敏感性亦不同.论文从转子动力学角度研究了齿轮联结的相交轴转子系统的动力学特性,可为此类转子系统的结构优化设计及运行维护提供理论依据.     

基于表面吸气的矩形截面涡激振动抑制及机理研究

随着桥梁跨度的增加,其风致振动问题逐渐凸显,发展简单、有效的风振控制措施对于保障桥梁结构的安全具有重要意义.将桥梁断面简化为矩形,通过数值模拟研究了侧表面双气孔吸气对矩形截面的涡激振动的抑制作用.研究表明：无量纲吸气流量是影响涡激振动抑制效果的决定性因素.当无量纲吸气流量■时,表面吸气对涡激振动的抑制效果达到最佳,矩形断面的振动幅值减小了99.73%,升力系数均方根值减小了90.37%,阻力系数平均值减小了32.55%.当■时,矩形截面的振动幅值仍然被有效地抑制,但吸气流量过大,侧表面上的边界层厚度变小,边界层内的剪切效应变强,引起背风面尾流旋涡的增强,最终导致矩形截面升、阻力系数的增加.     

血液静电泵的碟型阀门设计

以碟型阀门为对象,利用阀门流量与碟阀开角的相对指数关系,基于流体力学关于流量与压力差、阀门管道面积、流量系数间的关系,在压力差、阀门管道面积不变的条件下,建立了流量系数与开角的指数关系。从而得到阀门实际流量与碟阀开角、压力差、阀门管道面积的具体数值关系,以设计岀碟型阀套的合适的最小半径。将血液静电泵的设计原则应用于碟型阀门设计,选用不同的流量系数计算并绘制出不同阀门半径、碟阀开角与压力差的关系图。如何选择合理的阀门半径是本文研究目的所在,以保证阀门打开时,血流畅通无阻。再由碟阀半径、开角、流速,计算了雷诺系数并核对了所选流量系数;还研究了因阀门的快启导致血流施加于碟阀上的冲击力,进行了碟阀及其把柄的强度核验。     

基于大涡仿真的V锥流量计三维流场分析

研究V锥流量计测试精度优化问题.针对垃圾焚烧发电过程中管路结构对测量精度的影响,对流量计最佳测量位置进行研究.使用大涡方法(LES)对不同雷诺数(Re)下的V锥流量计测试流场进行了三维数值仿真,以明确测量过程中对管道结构的要求.通过使用大涡仿真方法能够获得更接近实验值测试的流量系数.在雷诺数(Re)不同时,由于流场中湍...     

旋转固体火箭发动机统一流场计算

为了进一步研究旋转对固体火箭发动机工作的影响,采用RSM湍流模型对内孔燃烧、内孔与端面同时燃烧管状装药旋转固体火箭发动机统一流场进行了仿真。采用UDF编程给出质量入口边界,获得了旋转条件下发动机内流场结构参数特点,并给予理论说明。计算结果表明,内孔燃烧装药发动机切向速度流场类似于典型的Rankine涡,端面和内孔同时燃烧装药发动机切向速度流场呈现出Rankine涡和由端面燃烧引起的强迫涡的复杂组合涡;在发动机前封头和喷管喉部涡核切向速度峰值非常大,使燃烧室前封头和喷管喉部工作环境显著恶化;旋转使发动机燃烧室压力沿径向逐渐增大,强迫涡附近的压力梯度远大于推进剂表面的压力梯度。     

Evaluation of flow maldistribution in air-cooled heat exchangers

Investigation of the evaluation of flow maldistribution in air-cooled heat exchangers is presented. The flow field in the inlet and return headers was obtained through the numerical solution of the governing partial differential equations including the conservation equations of mass and momentum in addition to the equations of the turbulence model. The effects of the number of nozzles, nozzle location, nozzle geometry, nozzle diameter, inlet flow velocity and the incorporation of a second header on the flow maldistribution inside the tubes of an air-cooled heat exchanger were investigated using a 3-D computational method. The results are presented in terms of the standard deviations of the mass flow rate and static pressure in addition to the distributions in the static pressure inside the inlet header of the air-cooled heat exchanger. The results indicate that reducing the nozzle diameter results in an increase in the flow maldistribution. 25% increase is obtained in the standard deviation as a result of decreasing the diameter by 25%. Increasing the number of nozzles has a significant influence on the flow maldistribution. A reduction of 62.5% in the standard deviation of the mass flow rate inside the tubes is achieved by increasing the number of nozzles from 2 to 4. The results indicate that incorporating a second header results in a significant reduction in the flow maldistribution. Fifty percent decrease in the standard deviation is achieved as a result of incorporation of a second header of 7 holes. The results indicate that the mass flow rate and the static pressure distributions become uniform at the inlet of the second pass.     

Approximation of involute curves for CAD-system processing

In numerous instances, accurate algorithms for approximating the original geometry is required. One typical example is a circle involute curve which represents the underlying geometry behind a gear tooth. The circle involute curves are by definition transcendental and cannot be expressed by algebraic equations, and hence it cannot be directly incorporated into commercial CAD systems. In this paper, an approximation algorithm for circle involute curves in terms of polynomial functions is developed. The circle involute curve is approximated using a Chebyshev approximation formula (Press et al. in Numerical recipes, Cambridge University Press, Cambridge, 1988), which enables us to represent the involute in terms of polynomials, and hence as a Bézier curve. In comparison with the current B-spline approximation algorithms for circle involute curves, the proposed method is found to be more accurate and compact, and induces fewer oscillations.     

圆渐开线平面插值样条及其应用

利用拼接的圆渐开线实现对平面上的数据点及其切向的插值,通过解决两点及其切向的圆渐开线插值,以及在各种不同情况下的插值处理方法,提供了圆渐开线平面插值样条的生成算法,由于圆渐开线为凸曲线,其曲率与弧长成反比,因此其样条曲线对插值曲线的形状控制是有利的,并可作为圆弧样条插值方法的一种扩展。     

Upstream wake-secondary flow interactions in the endwall region of high-loaded turbines

A detailed experimental and numerical investigation of the unsteady interaction of secondary flow vortices in turbine endwall region was performed with the effect of upstream periodic wakes. The flow field was investigated respectively in a linear turbine cascade and a turbine rotor. The study revealed the physical mechanisms of unsteady interaction between upstream wake and secondary vortices. The influence of the upstream wake on the performance of turbine endwall region was also discussed.The flow field at the exit of the turbine blade row showed a decrease in passage vortex strength and loss due to the upstream wake transport. Two interaction mechanisms are proposed whereby passage vortex loss decreases. They are the upstream wake-pressure side leg of the horseshoe vortex interaction and the upstream wake-passage vortex interaction. The transport of upstream wake can suppress the development of pressure side leg of the horseshoe vortex and passage vortex because of the “negative jet” influence of the wake.     

Investigation of the influence of swirl on a confined coannular swirl jet

Large Eddy Simulations are used to model a turbulent confined coannular combustor and examine the effects of swirl on the flow field and mixing. Three separate simulations with relatively high mesh resolutions and different swirl numbers have been carried out using a finite volume method on a Cartesian non-uniform structured grid. A localised dynamic Smagorinsky model is used to parameterize the sub-grid scale turbulence. The snapshots of the axial and swirl velocities and velocity vector fields show the complex flow patterns developing with increased swirl number and the rapid decay of axial momentum. Precessing vortex cores (PVC) were identified for all three cases and the mean axial velocity plots indicate that the upstream extremity of the vortex breakdown bubble shifts towards the inlet as the swirl number increases. The calculated power spectra indicate the distinct precession frequency for high swirl number. Probability density functions of axial velocity showed the changes of their distributions from approximately Gaussian to non-Gaussian with increased swirl number. The swirl has a large effect on the rate of decay of the axial velocity throughout the domain, whereas only has a significant effect on the decay of swirl velocity in the near field close to the jet inlet. The relation between swirl number and the axial extent of the recirculation zone is approximately linear. Radial plots of mean passive scalar and its variance also demonstrate an increase in the rate of mixing with increasing swirl number.     

Numerical Analysis of a Vortex Tube: A Review

Ranque–Hilsch vortex tube is a simple devise with no moving parts which could generate cold and hot air/gas streams simultaneously with compressed air/gas as a working fluid. The energy and flow separation in a vortex tube is highly depends on factors like nozzle shape, nozzle number, diameter and length of the vortex tube, inlet pressure, control valve, diaphragm hole size and cold mass fraction. As the energy separation and flow patterns in a vortex tube are highly complex and were not explained successfully by any researcher, a computational study of vortex tube flow and energy separation will give a better understanding about the physics and mechanism involved. Many researchers conducted computational fluid dynamic analysis of the vortex to have a deep insight about the process of flow separation. In this paper computational analysis of vortex by many researchers were presented along with the results obtained and suggestions to improve the performance of the vortex tube. Researchers considered Turbulence models which predict the performance precisely were discussed in the present paper. Researchers considered turbulence models like LES, k–ε, k–ω and RMS to predict the energy separation in vortex tube. Some researchers considered artificial neural networks (ANN) and Taguchi methods for their analysis. Comparison of the predictions with simulation results were also presented to give a clear idea for the reader about the CFD models prediction capabilities.     

Unsteady pulsating characteristics of the fluid flow through a sudden expansion microvalve

This paper investigates the unsteady characteristics of flow in a specific type of microvalve with sudden expansion shape. The resultant vortex structures cause different flow resistance in forward and backward flow directions. This may be used in applications such as a microvalve in micropump system and MEMS-based devices. A time-varying sinusoidal pressure was set at the inlet of the microchannel to produce unsteadiness and simulate the pumping action. The existence of block obstacle and expansion shoulders leads to various sizes of vortex structures in each flow direction. All simulation results are based on the numerical simulation of two-dimensional, unsteady, incompressible and laminar Navier–Stokes equations. Two fundamental parameters were varied to investigate the vortex growth throughout the time: the frequency of the inlet actuating mechanism (1 Hz ≤ f ≤ 1,000 Hz) and the amplitude of the inlet pressure. In this way, one can see the effect of actuation mechanism on the onset of separation and follow the size and duration of the vortex growth. In order to better understand the effect of geometry and frequency on flow field, the pressure and velocity distributions are studied through one cycle. Strouhal number is calculated for frequency, and a critical value of f = 250 Hz is found for St = 1. The obtained results provide a deep insight into the physics of unsteady flow in valveless micropumps and leads to better use of current design as a part of microfluidic system.     

Simulation of the effect of geometric parameters on tangentially injected swirling pipe airflow

A realizable k–ε turbulence model is employed to study compressible tangentially injected swirling flow in the nozzle of air–jet spinning. The effects of the nozzle geometric parameters (the injection angle, the diameter, number and position of the injector, nozzle length and chamber diameter) on both the flow and yarn properties are investigated. The simulation results show that some factors, such as velocity distribution, reverse flow in the upstream of the injector and vortex breakdown in the downstream caused by the nozzle geometric variation, are significantly related to fluid flow, and consequently to yarn properties. With increase in the injection angle or injector diameter or injector number, in the downstream of the injector, velocities will increase somewhat, and the locations of vortex breakdown move downward. As injector number increase with the total injection area being kept constant, the strength of vortex breakdown in the downstream of the injector will slightly increase. A larger reverse flow will be not helpful to draw the fibers into nozzle, as the injector position is closer to the nozzle inlet. The flow is more turbulent for a larger chamber diameter.