受电弓下沉对其气动和声学行为的影响

为研究受电弓下沉对其气动行为和声学行为的影响,建立了考虑安装平台的高速受电弓计算模型,基于计算流体力学和声学类比理论,对受电弓的气动和声学行为展开数值模拟。受电弓下沉高度分别设为100、200、300、400和500 mm,通过风洞试验验证了数值计算方法的合理性。仿真结果表明：随着受电弓安装平台下沉高度的增大,绝缘子和底架迎风面正压减小,受电弓气动阻力减小;安装平台气动阻力先增大后减小,通过优化腔体过渡倾角可显著减小安装平台所产生的气动阻力;当安装平台下沉高度为300 mm、腔体倾角为30°时,受电弓开口、闭口运行时其气动阻力分别减小2.0%、1.8%,整车阻力分别减小1.4%和1.1%;受电弓气动噪声具有明显的主频特性,主要频率约为330 Hz,能量主要集中在400~2500 Hz范围内;安装平台下沉后,绝缘子和底架周围流体流速减小,绝缘子和底座的表面声功率显著降低;安装平台下沉300 mm时,受电弓远场气动噪声最大声压级减小2.02 dBA,平均声压级减小1.31 dBA;受电弓下沉可改善其气动和声学性能。     

高速列车风道传声特性及其优化设计

空调系统噪声是高速列车静置噪声的主要噪声源之一,改善风道传声特性是其减振降噪的关键所在。针对某高速列车阻抗复合消声风道结构,采用FE-SEA混合法,建立了风道传声特性分析模型,计算了100～3 150 Hz频率区段的风道传声特性,同时,基于声学有限元法计算了风道结构的声学模态,并据此分析了风道传声损失峰值和谷值的成因。为提高风道传声损失,分别从声学阻性和抗性优化两方面着手,对风道进行优化,包括选材、吸声包数量和位置等优化设计。计算结果表明：吸声选材优化可显著提高其传声损失,最大可达11.3 dB;吸声包数量和位置优化可提高其传声损失4.8 dB;阻抗复合优化方案最高可提高风道传声损失15.6 dB。相关结论可为高速列车空调系统减振降噪提供参考。     

Simulation on a car interior aerodynamic noise control based on statistical energy analysis

How to simulate interior aerodynamic noise accurately is an important question of a car interior noise reduction. The unsteady aerodynamic pressure on body surfaces is proved to be the key effect factor of car interior aerodynamic noise control in high frequency on high speed. In this paper, a detail statistical energy analysis (SEA) model is built. And the vibra-acoustic power inputs are loaded on the model for the valid result of car interior noise analysis. The model is the solid foundation for further optimization on car interior noise control. After the most sensitive subsystems for the power contribution to car interior noise are pointed by SEA comprehensive analysis, the sound pressure level of car interior aerodynamic noise can be reduced by improving their sound and damping characteristics. The further vehicle testing results show that it is available to improve the interior acoustic performance by using detailed SEA model, which comprised by more than 80 subsystems, with the unsteady aerodynamic pressure calculation on body surfaces and the materials improvement of sound/damping properties. It is able to acquire more than 2 dB reduction on the central frequency in the spectrum over 800 Hz. The proposed optimization method can be looked as a reference of car interior aerodynamic noise control by the detail SEA model integrated unsteady computational fluid dynamics (CFD) and sensitivity analysis of acoustic contribution.     

Numerical analysis of impulse waves discharged at the exit of a model tunnel

Impulse waves are micro-pressure waves, which always occur at the tunnel exit when a high-speed train is moving inside a train tunnel. The air around the train nose is compressed and compression waves are induced. The impulse wave is discharged at the exit of a train tunnel when a compression wave propagates outside of the tunnel exit. Impulse waves are weak-strength pressure waves, which lead to noise and other environmental problems. In order to efficiently control the impulse wave at the exit of a train tunnel, numerical studies on investigating the generation and propagation of the impulse wave were carried out. A 2-D axisymmetric model tunnel was simulated at different operating conditions. Different Mach numbers of compression waves were varied to induce different magnitudes of impulse waves at the tunnel exit. In addition, compression waves with different pressure gradients were assumed at the tunnel entry to check their effects on the generation of impulse waves. In order to observe impulse waves at far field, five monitor points were installed behind the tunnel exit to record pressure histories as impulse waves moved through these locations. The detailed magnitudes and characteristics of impulse waves were obtained in the present studies.     

A computational analysis of the airflow in a twin-track subway tunnel with a sliding-curtain to improve ventilation performance

A computational model of an actual Seoul subway tunnel was analyzed in this study. The computational model was comprised of one natural ventilation shaft, two mechanical ventilation shafts, one mechanical air supply, a twin-track tunnel and a train. The natural ventilation shaft discharges and supplies air due to the train’s movement. The mechanical ventilation shaft and the mechanical air supply discharges and supplies, respectively, the airflow from the axial flow fans in the middle of the ducts of the shafts. A sliding-curtain was installed in the tunnel. The objective of this study was to numerically investigate train-induced airflow in the twin-track subway tunnel with natural and mechanical ventilation shafts and an installed curtain. The numerical analysis characterized the aerodynamic behavior and performance of the ventilation system by solving three-dimensional turbulent Reynolds-averaged Navier-Stokes equations. ANSYS CFX software was used for the computations. The airflow velocity from the computational results was validated by experimental results. Understanding the flow pattern of the train-induced airflow in the tunnel is necessary to improve ventilation performance. The ventilation and aerodynamic characteristics in the tunnel, including train-induced airflow, were investigated by analyzing the volume flowrate at the exits of the ventilation shafts and the velocity in the tunnel. The computational results were compared to cases with and without a curtain installed in the twin-track tunnel. As the train passed the mechanical ventilation shafts, the quantity of discharged-air in the ventilation shafts decreased rapidly. The flowrate at the exits of the ventilation shafts was gradually recovered with time, after the train passed the ventilation shafts. The airflow at the natural shaft and mechanical ventilation shaft 2, which was closest to the curtain, was increased. The computational results showed that the installed curtain can improve ventilation performance in the tunnel.     

高速列车单车通过隧道压力波的研究

采用计算流体力学的数值计算方法对基于三维、瞬态、可压缩Navier-Stokes方程和κ-ε两方程紊流模型进行求解,模拟高速列车单车通过隧道时列车外流场的特性,分析高速列车单车通过隧道的压力波特性及阻力变化规律。结果表明列车单车通过隧道的压力波最小负压值与速度为二次函数的关系,列车阻力主要由压差阻力构成。研究结果可为解决隧道空气动力学问题提供参考依据。     

节气门急速开启过程流动噪声数值分析与研究

研究了节气门运动对流动噪声的影响。采用计算流体力学与计算声学耦合方法,并结合运动网格技术,实现对节气门由关闭向全开位置急速转动过程时空气瞬态流动引起噪声形成的三维数值模拟,分析了节气门处于不同转角时刻,空气流场与流动噪声的变化规律。在节气门转动初期,节气门后侧流动区域有涡流形成,节气门前后两侧的压力发生陡降,在节气门上边缘和下边缘附近产生两个流动噪声区,随后在节气门下游逐渐合并。流动噪声声功率级先增加然后逐渐减小,并接近稳定,节气门开度在40°附近时,声功率级达到最大。随着节气门开度的继续增加,节气门后侧的涡流逐渐减弱,节气门前后两侧的压力降逐渐减小。噪声场时域-频域计算结果发现,节气门噪声属于中低频段宽频噪声,其中大约100Hz以下的低频噪声占主要贡献量,声压级较高,并且声压没有随着测点与节气门的距离增加而明显衰减。控制节气门流动噪声的重点在于减少低频噪声。     

A numerical simulation of train-induced unsteady airflow in a tunnel of Seoul subway

This study has been conducted to investigate numerically the characteristics of train-induced unsteady airflow in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train is applied. The validation of the present study has been carried out against the experimental data obtained by Kim and Kim [1] in a model tunnel. After this, for the geometries of the tunnel and subway train which are very similar to those of the Seoul subway, a three-dimensional unsteady tunnel flow is simulated. The predicted distributions of pressure and air velocity in the tunnel as well as the time series of mass flow rate at natural ventilation ducts reveal that the maximum exhaust mass flow rate of air through the duct occurs just before the frontal face of a train reaches the ventilation duct, while the suction mass flow rate through the duct reaches the maximum value just after the rear face of a train passes the ventilation duct. The results of this study can be utilized as basic data for optimizing the design of tunnel ventilation systems.     

高速列车通过隧道时的压力波动问题

高速列车通过隧道时将会在隧道内引起相当复杂的气体压力波动,这是由于列车进入隧道时在隧道入口产生的压力波在隧道内来回传递并与列车经过时的气体压力扰动相互叠加的结果。从车体强度设计和列车运行安全性角度考虑,希望了解隧道内可能的最大气体正、负压力大小及其发生位置;气体压力波动与列车运行速度的关系。通过流体力学方程三维动态数值计算,仿真分析列车高速通过隧道的过程。计算结果证明了入口压力波效应与列车经过的扰动效应的叠加关系,得到列车通过时隧道内最大正压和最大负压发生的可能位置,以及最大正压值与最大负压值与车速间的关系式。可为高速铁路隧道和高速列车设计提供参考。     

旋片式真空泵排气噪声问题的研究

利用Virtual. Lab Acoustic声学仿真软件,采用声学有限元法对旋片式真空泵排气过程中的气动噪声进行仿真,得到了在0~5000 Hz频率范围内的排气噪声的相关分布特征。同时,为研究旋片式真空泵排气空间内不同部位对排气噪声的贡献量,在模型中选择5个对噪声影响较大部位的声压级频率响应曲线进行分析,为探究降低旋片式真空泵的排气噪声的途径提供了重要参考,对同类真空泵噪声问题处理也有重要的参考价值。     

强风雨环境下高速列车运行安全特性

为确保高速列车在强风雨环境下安全运行,结合EULER-LAGRANGE方法和计算多体动力学方法,系统地研究风雨环境下高速列车的气动特性及运行安全特性。基于非球形雨滴,建立高速列车空气动力学计算模型,并验证计算模型的准确性,进而计算强风雨环境下作用于高速列车的气动载荷。建立高速列车车辆系统动力学模型,计算强风雨载荷作用下的高速列车运行安全特性。研究结果表明,在不同风速下,高速列车的侧力、升力、侧滚力矩及摇头力矩均随降雨强度的增加而增大,且与降雨强度近似成线性关系,对于点头力矩,当风速较小时,点头力矩随降雨强度的增加而增大,而当风速较大时,点头力矩随降雨强度的增加而减小。与单纯的强风环境相比,降雨使得高速列车的运行安全特性进一步恶化,在不同风速下,高速列车脱轨系数、轮重减载率、倾覆系数及轮轴横向力均随降雨强度的增加而增大,特别是当风速接近于临界风速时,降雨对高速列车运行安全特性的影响显著。当降雨强度为500 mm/h时,由不同运行安全指标确定的高速列车安全运行的临界风速降低2.3~4.2 m/s。研究结果可为高速列车在风雨环境下的安全限速提供参考。     

可调频Helmholtz共振器声学性能

传统的Helmholtz共振器属于被动消声结构,只要结构确定,其消声频率就被确定,然而,实际噪声环境中,频率经常发生改变。针对这种情况,设计出一种可调频Helmholtz共振器。利用压电陶瓷替代Helmholtz共振器的刚性背板,通过调节施加在压电陶瓷上的电压,改变其腔体体积,使得消声频率偏移。结果表明,压电陶瓷在施加400V电压后,可以产生0.515mm的位移;Helmholtz共振器在不同电压下,共振频率偏移了80Hz;设计的自适应控制程序可适应频率多变的噪声环境。     

轴向柱塞泵壳体降噪区域识别

为了精确识别轴向柱塞泵壳体降噪区域,首先,搭建液压-多体动力学耦合模型,求解结构噪声激振力;然后,分析零部件模态并试验验证,建立装配体有限元模型,开展基于模态的振动响应分析,通过振动实验验证模型准确性,搭建轴向柱塞泵声学边界元模型,分析其辐射噪声特性;最后,基于声学传递向量原理,开展模态及板面声学贡献量分析,对壳体噪声辐射板面进行合理划分,分析其对关键频率下辐射噪声的贡献量。研究表明:轴向柱塞泵振声模型具有良好的准确性;某板面在辐射噪声突出的1350 Hz频率下,其声学贡献量达到46.1%。精确识别了轴向柱塞泵壳体降噪区域,为其降噪优化设计提供有效指导。     

一种含次级通道在线辨识的窄带主动噪声控制系统

分析了噪声危害设备产生的谐波噪声,特别是以500 Hz或600 Hz以下的低频成分为对象,介绍了主动噪声控制(ANC)技术的原理、意义及发展现状。在实际声学场所,由于控制系统易受初级噪声功率、残余噪声幅值等因素影响而不稳定。在分析控制系统收敛条件的基础上,通过对系统误差引入一个比例因子从而改进系统模型,并以一维管道为实验平台,基于高速数字信号处理器(DSP)设计了含次级通道在线辨识的主动噪声控制器。实验结果表明,在250 Hz左右的频段上能够达到16 dB的降噪效果。     

拖车转向架气动噪声数值研究

拖车转向架作为高速列车最主要的气动噪声声源,由于其结构复杂、细小部件多、周围涡流分布紊乱等,对拖车转向架的气动力和气动噪声认识甚少。采用定常RNG k-ε湍流模型与宽频带噪声源模型对拖车转向架的气动阻力、气动升力和气动噪声声源进行初步探讨,并结合非定常大涡模拟与Lighthill声学比拟理论对其进行远场气动噪声分析。计算结果表明:较大漩涡存在于空气弹簧与抗蛇形减振器之间、迎风侧轴箱与构架侧梁外侧的邻近区域;气动阻力、气动升力与运行速度的平方成正比关系,占总气动阻力最大的部件依次为构架(24.02%)、轮对(19.30%)、枕梁(18.08%)、制动闸片、抗侧滚扭杆、制动盘、构架支架和空气弹簧,枕梁的气动升力最大且占总气动升力的157.88%左右;轮对、构架、制动闸片、制动盘、枕梁、垂向减振器、抗侧滚扭杆等凸起部位的迎风侧表面为拖车转向架的气动噪声源,且构架对拖车转向架总噪声的贡献量最多,其次为轮对,然后为盘形制动装置和枕梁,抗侧滚扭杆、垂向减振器、空气弹簧和横向减振器对总噪声的贡献量较少。拖车转向架远场气动噪声是宽频噪声,具有噪声指向性、衰减性和幅值特性等,主要能量集中在28~56 k Hz频率范围内,中心频率为50 Hz、100 Hz、160 Hz在低频部分能量较大且分布规律不随运行速度的改变而变化。     

采用计算气动声学研究高速列车表面偶极子声源外辐射的指向性

将边界元声场分析方法与流体动力学分析技术有机结合起来,在某高速列车边界元模型中,导入流场脉动压力数据并在声学网格上转换成气动偶极子声源边界条件,采用直接边界元算法实现了基于表面偶极子声源的列车气动噪声外辐射声场的数值仿真,在此基础上对列车气动噪声外辐射场声压力分布规律以及车身表面偶极子源外辐射的指向性等特性进行了分析。研究表明:列车两侧的正横方向为车身表面偶极子声源主要水平声辐射方向,在离声源中心25m距离上可达80dB左右;车顶上方为主要横向声辐射声域,25m距离上可达83dB;频率越高,车身表面偶极子声源的指向性越强。     

汽车门密封处的气动噪声研究

使用数值模拟方法对汽车门密封处的气动噪声进行了模拟,在得到流场的基础上,应用FW-H声学类比方程分析了由流动诱发的气动噪声.通过数值模拟观察到了涡结构的脱体及门密封处腔体内部的自激振荡过程,并针对其中一个自激振荡循环做了说明与分析.得出了由流动诱发噪声的声压-频率曲线,发现采用流速30m/s时,汽车门密封处流动噪声声压级在70db以下;频率在2000Hz以内的峰值为349Hz及其高次谐波噪声,2000Hz以上出现了非349.65Hz倍频的峰值,体现了伴流模式诱发声场的复杂性.     

Structural optimization of an automobile transmission case to minimize radiation noise using the model reduction technique

Vehicles should provide a comfortable environment for passengers. The noise from the transmission case is one of the causes of an uncomfortable environment. The transmission is composed of gears, shafts, bearing and cases. When transmission activity occurs, noise is transferred to the passengers through the transmission case. Design of the transmission case is performed in order to reduce the transmission noise. Acoustic analysis is carried out and structural optimization is utilized for the design to reduce the noise. Generally, the boundary element method (BEM) has been utilized for acoustic analysis. However, it is difficult to utilize the boundary element method in structural optimization because the cost to calculate the sensitivity information is fairly expensive. Instead, the finite element method (FEM) is employed for calculating the radiation noise of the transmission. Radiation noise is considered as the total noise from the transmission. Radiation noise is calculated at the outside of the transmission case and it can be expressed indirectly by multiplication of the velocity in the normal direction of the finite elements, the radiation efficiency and the characteristic acoustic impedance. The high frequencies are dominant for the transmission noise and the radiation efficiency is 1 at the high frequency range. Since the characteristic acoustic impedance has a constant value, the noise is the same as the norm of the velocity. The velocity of each finite element is calculated from modal analysis and the noise is expressed based on the average velocity of the vibrating structure. However, a long computation time is required to calculate the noise in a large scale structure such as a transmission. Thus, the entire model of transmission is condensed into the reduced model by the model reduction technique. The component mode synthesis (CMS) method is employed for the model reduction technique. The CMS method is an effective method for dynamic analysis of large and/or complex structures. The reduced model keeps the dynamic characteristics of the entire structure and it is used for structural optimization. In structural optimization, the design variables are the thicknesses of the groups of the transmission cases, the objective function is the mass of the structure and a constraint is imposed on the noise. An alternative formulation is made by exchanging the objective and constraint functions. The optimization results are discussed in terms of practical application.     

基于声学灵敏度的汽车噪声声-固耦合有限元分析

车身结构声辐射的预测对于噪声的控制和降低有着重要的意义.首先推导了声-固耦合有限元的控制方程,并得到模态参与因子和板块声学贡献量的计算方法;然后以某商务车为研究对象,应用虚拟试验场技术,建立声-固耦合有限元模型,包括车身与汽车室内空腔的有限元模型;选择车身与底盘的连接点作为声学灵敏度分析的激励点,采用声-固耦合有限元法,计算得到各悬置点至驾驶员耳旁的声学灵敏度;从声学灵敏度分析结果中发现,车身模态在共振峰70、138、200 Hz处均存在较大的峰值;研究这三个峰值的频率点及其结构,并计算结构模态和声学模态参与因子以及车身板块的声学贡献量,最终得出对车内声学响应影响最大的板块和结构模态.     

自适应调频声衬及其控制系统设计

为克服现有声衬结构固定、敏感频率无法调节的弊端,提出了一种逆压电效应的调频式声衬结构。该声衬由颈部、共振腔以及压电膜片组成亥姆霍兹共振器。采用有限元法对声衬结构的固有频率、声场分布进行了计算,研究了压电膜片变形与共振频率偏移的关系。在阻抗管内对压电声衬致动前后系统的传递损失进行了对比,系统传递损失峰值频率与驱动电压呈线性关系,灵敏度为0.1Hz/V。在建立控制电压-驱动电压-噪声频率的对应关系的基础上,提出了一种基于光敏电阻的直流升压电路,采用LabVIEW软件编制了压电声衬的自适应控制程序,当噪声频率从746变化至788Hz时,驱动电压由110V自动升高至420V,声衬始终工作于共振状态,实现了宽频噪声的自适应控制。