收集口形状和角度对汽车风洞试验段轴向静压因数的影响

为研究风洞收集口形状和角度对试验段轴向静压因数的影响,通过数值仿真和试验验证研究翼型收集口在多种角度下轴向静压因数的变化,并与平板型收集口对比.结果表明:收集口形状对轴向静压因数变化规律没有影响,轴向静压因数总是随开口角度的增大而减小;对于同一形状收集口,只在上方张开某一角度比在两侧张开相同角度的轴向静压因数略低.收集口角度变化对轴向静压因数会产生规律性影响:随收集口角度增大,从剪切层外部特别是上方进入到射流核心区的流量增加,导致核心区流速增加,从而导致轴向静压因数降低.     

某型涡扇发动机涡轮过渡流道一体化优化设计

研究大涵道比涡扇发动机涡轮过渡流道优化问题,针对扩张通道轴向长度较短,内部流动十分复杂,边界层气流容易分离等难点,为提高过渡流道气动性能,利用全三维数值仿真的方法对某型大涵道比涡扇发动机涡轮过渡流道进行了数值仿真,并采用遗传算法对初始流道进行了气动性能优化设计.仿真结果表明,过渡流道气动性能对其几何形状变化十分敏感,流量相同条件下,采用优化设计后,涡轮过渡流道压力系数提高,总压损失系数降低,并且流道稳定工作范围也得到改善,结果证明了优化方法的有效性和可行性.     

基于数值计算的高速列车气动阻力风洞试验缩比模型选取方法

为给高速列车气动阻力风洞试验模型选取提供更多的参考依据,通过计算流体力学(Computational Fluid Dynamics,CFD)方法,研究不同比例的高速列车缩比模型对气动阻力风洞试验结果的影响.首先,计算得到开口式风洞测试段的静压系数分布曲线,为高速列车气动阻力测量试验模型的长度选择以及摆放位置提供依据;其次,通过数值计算得到全尺寸模型列车在明线运行时,以及不同比例的模型列车在风洞中运行工况下的气动阻力信息,并从阻塞效应和雷诺数的变化,以及风洞试验段内静压分布的影响这3个方面对列车模型的气动阻力结果进行分析,得到在所研究风洞中较合理的列车缩比模型比例选取范围.这种以CFD为基础进行数值仿真,选取风洞试验中列车模型比例及试验测试位置的方法,为在地面交通工具风洞中进行高速列车模型气动阻力试验的缩比模型选取提供一定依据.     

压力平衡口对开口式汽车模型风洞驻室流场影响的数值仿真

为尽可能真实地建立汽车测试环境,对开口式汽车模型风洞驻室试验段流场品质进行数值仿真,研究在开设压力平衡口前后的流场品质,并对不同面积和形式的压力平衡口工况进行数值仿真,得到不同试验段内流场品质的计算结果.通过比较分析得出结论:有压力平衡口时,特别是压力平衡口的面积为140 m×140 m时,汽车模型风洞驻室试验段最有利于汽车性能测试.     

分布抽吸率对整车风洞试验段流场影响的数值模拟

为探讨适用于整车风洞的分布抽吸率,采用计算流体力学（Computational Fluid Dynamics,CFD）方法研究经边界层控制后的试验段流场．针对不同分布抽吸率下的试验段,利用FLUENT对流场进行模拟,然后计算边界层位移厚度、静压因数和气流偏角．二维和三维的数值模拟结果均表明,试验段边界层的位移厚度随分布抽吸率的增加而减小;当分布抽吸率达到某一数值后,若继续增大,那么边界层的位移厚度将基本保持不变．研究结果对风洞建设及试验时分布抽吸率的选取有参考意义．     

低雷诺数湍流模型的网格特征

低雷诺数模型目前主要应用于二维简单流动的数值仿真中,为研究该湍流模型在三维复杂流动计算中的网格特征,选取不同系列的车身面网格尺寸、车身壁面第一层边界层与壁面法向高度以及边界层层数等3组网格参数,利用ANSYS对阶背式MIRA模型外流场进行数值仿真.数值仿真结果与风洞试验的结果对比表明：数值计算得到的车身表面平均y+值随面网格尺寸增加而呈现减小趋势;网格方案对气动力因数和车身表面压力因数分布影响显著,气动阻力因数仿真值与试验值误差的变化区间为0.83%~7.93%,气动升力因数误差变化区间为10%~104%;气动阻力因数和气动升力因数均随着边界层层数的增加而增大,边界层层数为5时可以得到兼顾气动力因数精度和车身表面压力因数精度的较优仿真结果.     

计量用低速风洞结构参数仿真研究

为准确分析风洞结构参数对所产生的风场稳定性的影响规律,以现有低速风洞为蓝本,通过改变其试验段结构参数建立多个不同参数试验模型;采用ansys CFD对建立的多个新模型进行结构流体仿真,对仿真结果进行数据拟合,找出风洞收缩段曲线结构参数变化对试验段轴向风速梯度和法向风速均匀性的影响;仿真实验结果表明,试验段法向中心面的有效试验区的均匀性系数随着收缩段长度增加而减小,到一定程度趋于稳定,风洞模型在L＞ 23 cm后风场均匀性系数基本处于稳定,试验段前半段的风速轴向梯度明显大于后半段的风速轴向梯度,有效试验区域多集中在后半段,风洞模型中轴向有效试验区域x＞(10～15) cm,可以为风洞的设计提供可靠参考.     

基于CORDIC算法的360°角度传感器的设计

一维霍尔板型角度传感器无法测量0～360°的角度,采用4个霍尔器件的联合测角技术和CORDIC算法可实现0～360°范围内的角度测量。文章详细描述了4个霍尔器件联合测角技术的测角原理及实现算法,并引入了符号幅值表示法,即先利用正弦和余弦的幅值进行0°～90°范围内的反正切CORDIC运算,再根据正弦和余弦正负号(符号)的不同组合实现角度从0°～90°到0°～360°的映射。Modelsim平台仿真验证了该方法的准确度和精度,仿真误差小于0.01%,实测总误差不大于0.05°。     

一种基于磁传感器的MEMS陀螺标定方法

根据微型航姿测量系统各传感器的特点,研究出了一种基于磁传感器输出的MEMS陀螺标定方法,并根据MEMS陀螺误差参数模型设计相应的补偿算法,分别对MEMS陀螺的零偏和标度因数误差进行了补偿。与传统标定方法相比,该方法实现简单,适用于现场标定。实验结果表明,该标定方法能够有效地提高MEMS陀螺测量精度,补偿后陀螺在静态条件下2分钟内,俯仰角漂移小于0.035°,倾斜角漂移小于0.15°,航向角的漂移小于0.2°。当陀螺三轴均有角速率输入时,在角速度小于25°/s情况下误差都能保持在±2°以内。     

海缆铠装结构锚固性能有限元分析

基于有限元显式算法,通过预紧、加载载荷作用次序,研究海缆铠装层的锚固结构在工作载荷和破断力下的承载能力,并对影响锚固性能的参数进行敏感性分析.数值仿真结果显示：在破断力作用下,法兰内壁与钢丝接触位置产生明显压痕,钢丝断裂位置发生在钢丝在锚固出口位置.增加锥形锚固的内锥角可降低钢丝轴向拉伸量,减缓法兰的不利应力.同时.在较低摩擦因数下具有较大内锥角的接头盒依旧具有良好的机械性能.所设计的内锥形锚固维修接头盒能满足施工过程中的最大拉伸载荷要求.     

静止和旋转孤立车轮局部流场的评价

为研究车轮周围流场特征,分别对某孤立车轮静止和旋转工况下周围流场进行数值研究,并给予试验验证.计算采用定常雷诺时均纳维斯托克斯方程.在1∶15的模型风洞中进行试验.数值模拟结果与试验数据吻合.针对数值模拟结果,详细分析静止和旋转孤立车轮周围流场的流动情况、表面压力因数、气动阻力因数和气动升力因数等,得到孤立车轮旋转对车轮附近局部流场的影响以及形成机理.车轮的转动使总体压差减小,降低气动阻力和升力,改善气动性能。     

面向攻角变化的风洞流场模型预测控制器

目前已有的控制方法难以满足大飞机研制对风洞流场的精度要求.鉴于此,采用多变量模型预测控制方法设计流场控制器.为提高抵抗攻角扰动的能力,使用攻角变化量动态补偿静压的预测值.考虑风洞实验工况较多,采用多控制器融合方法解决新工况建立预测模型的问题.为保证控制器的实施,给出基于一阶惯性加滞后近似模型的控制器参数整定方法.通过实际吹风实验验证风洞预测控制器能够有效调节风洞流场,使吹风实验中流场参数的精度达到大飞机研制要求.     

Performance of a bend-diffuser system: Experimental and numerical studies

The turbulent flow inside a combined bend-diffuser configuration with a rectangular cross section is experimentally and numerically studied. The experimental study includes the outer and inner-wall-pressure measurements and the overall system/diffuser loss determination. Simulation is performed using the high-Reynolds number k-ε turbulence model improved by the low-Reynolds number k-ε turbulence model near the walls, because of its success to predict the flow with strong adverse pressure gradient. So the present paper provides a numerical procedure for the calculation of turbulent flow in a sequence curved, expanding passages, with emphasis on the bend-diffuser configuration system consisting of a 90° bend followed by a diffuser with different expanding angles ranges from 2θ = 6-30° at different inflow Reynolds numbers. Satisfied comparisons with reported experimental data in the literature as well as that carried out by the present authors at the heat engine laboratory of Menoufiya university show that the numerical method with the utilized closure turbulence model reproduces the essential features of upstream curved flow effects on the diffuser performance. The effect of spacer length (between the bend and diffuser) is also experimentally and numerically included. The results show that there is an optimum diffuser angle which depends on the inflow Reynolds number and produces the minimum pressure loss and hence good performance of such complex geometry is obtained.     

Behavior of microdroplets in diffuser/nozzle structures

This paper investigates the behavior of microdroplets flowing in microchannels with a series of diffuser/nozzle structures. Depending on the imposed flow direction, the serial structures can act either as a series of diffusers or nozzles. Different serial diffuser/nozzle microchannels with opening angles ranging from 15° to 45° were considered. A 2D numerical model was employed to study the dynamics of the microdroplet during its passage through the diffuser/nozzle structures. The deformation of the microdroplet was captured using a level set method. On the experimental front, test devices were fabricated in polydimethylsiloxane using soft lithography. T-junctions for droplet formation, diffuser/nozzle structures and pressure ports were integrated in a single device. Mineral oil with 2% w/w surfactant span 80 and de-ionized water with fluorescent worked as the carrier phase and the dispersed phase, respectively. The deformation of the water droplet and the corresponding pressure drop across the diffuser/nozzle structures were measured in both diffuser and nozzle configurations at a fixed flow rate ratio between oil and water of 30. The results show a linear relationship between the pressure drop and the flow rate. Furthermore, the rectification effect was observed in all tested devices. The pressure drop in the diffuser configuration is higher than that of the nozzle configuration. Finally, the pressure measured results with droplet and without droplet were analyzed and compared.     

声学风洞的设计与仿真

声学风洞优化设计问题随着航空交通运输业的发展,飞机产生的噪声问题日益引起人们的重视。为此,对地面实验设备就提出更高的要求,开展了航空声学风洞的研究。针对传统声学风洞靠经验和工程估算的设计方法准确性差的问题,提出采用数值仿真的方法对将要建造的声学风洞内流场进行建模仿真。得到给定速度下,得到风洞整体内流场的速度及压力分布,比较了风洞各段的压力损失系数和轴线的速度分布,并结合气动声学FW-H方法给出了各段的声压级。结果表明,通过数值仿真可对风洞前期优化设计起到指导作用。     

底部导流板形式对高速列车气动阻力的影响

为减小高速列车运行时的气动阻力,设计直式、斜式、内圆弧式和外圆弧式等4种转向架前后底部导流板的高速列车模型.通过风洞试验验证数值模拟方法的有效性,采用数值计算分析底部导流板对列车气动阻力和底部流场的影响.结果表明：不同形式底部导流板的列车总阻力相差可达20%,其中头车气动阻力因数极差值最大为0.062.导流板影响列车底部气流速度和转向架区域压力分布,其导流作用使得转向架区域气动阻力和转向架的阻力同时改变.转向架前后导流板的导流效果越好,转向架区域的气动阻力越小;同时,气流冲击使得转向架上的滞止压力增大;在二者的共同作用下高速列车的总阻力存在一个较小值.底部采用直式导流板对降低全车气动阻力的效果最好.     

Three dimensional numerical simulations of long-span bridge aerodynamics, using block-iterative coupling and DES

The design of long-span bridges often depends on wind tunnel testing of sectional or full aeroelastic models. Some progress has been made to find a computational alternative to replace these physical tests. In this paper, an innovative computational fluid dynamics (CFD) method is presented, where the fluid-structure interaction (FSI) is solved through a self-developed code combined with an ANSYS-CFX solver. Then an improved CFD method based on block-iterative coupling is also proposed. This method can be readily used for two dimensional (2D) and three dimensional (3D) structure modelling. Detached-Eddy simulation for 3D viscous turbulent incompressible flow is applied to the 3D numerical analysis of bridge deck sections. Firstly, 2D numerical simulations of a thin airfoil demonstrate the accuracy of the present CFD method. Secondly, numerical simulations of a U-shape beam with both 2D and 3D modelling are conducted. The comparisons of aerodynamic force coefficients thus obtained with wind tunnel test results well meet the prediction that 3D CFD simulations are more accurate than 2D CFD simulations. Thirdly, 2D and 3D CFD simulations are performed for two generic bridge deck sections to produce their aerodynamic force coefficients and flutter derivatives. The computed values agree well with the available computational and wind tunnel test results. Once again, this demonstrates the accuracy of the proposed 3D CFD simulations. Finally, the 3D based wake flow vision is captured, which shows another advantage of 3D CFD simulations. All the simulation results demonstrate that the proposed 3D CFD method has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of long-span bridges and other slender structures.