分支谐振型液压脉动衰减器动态特性分析

对分支谐振型液压脉动衰减器用CFD(Computational Fluid Dynamics,计算流体动力学)分析软件进行计算,分析共振腔结构与衰减器动态特性的关系。在层流状态下,考虑流体的可压缩性,利用M序列压力信号激励,对衰减器进行CFD模拟,利用FFT(Fast Fourier Transform,快速傅立叶变换)得出其频率特性,比较了共振腔容积相同但直径和长度不同的衰减器的频率响应和插入损失;利用阶跃压力信号模拟压力冲击,比较了它们内部流场。设计了频率特性相同但共振腔容积不同的衰减器,比较了它们的性能。利用分布参数法对共振腔结构与衰减器基频的关系进行了分析。结果表明:衰减器的固有频率特性在一定程度上与共振腔的直径和长度相关,当共振腔直径-长度比小于1并逐渐减小时,衰减器基频也减小;当其大于1并逐渐增大时,衰减器的基频变化很小,因此减小共振腔直径-长度比可以减小衰减器的体积,同时保持共振频率不变。     

穿孔和非穿孔消声器压力损失研究

本文利用三维CFD方法,研究了抗性消声器内部流体动力学仿真和压力损失计算的过程,分析了四种穿孔和非穿孔单腔消声器的流场流速和压力分布,研究了相应的压力损失随入口流速的变化趋势.得出结论:,穿空管消声器的流体动力学性能要好于非穿孔类消声器,对膨胀腔冲击比较小;在相同边界条件下,穿孔管消声器的压力损失大于非穿孔类消声器.对复杂抗性消声器的设计有比较好的参考价值.     

不同进/出口分布的消声器性能研究

基于Virtual.Lab的声学有限元模块对简单扩张腔消声器的传递损失进行了数值模拟,并和平面波理论进行了对比,模拟了在不同的进出口分布的情况下的传递损失并进行了对比分析。基于Fluent流体仿真软件计算了不同的进出口分布的情况下的扩张腔消声器的压力损失大小。结果表明,当进口或者出口位于扩张腔轴线上时,另一个出口或者进口偏离轴线的距离越大,消声效果越好而流场效果越差;当进出口同时偏离轴线时,偏离的距离越大,消声效果和流场效果都会变的越差。     

基于Fluent的FSAE赛车消声器的优化设计

采用SolidWorks软件建立消声器三维实体模型,应用Fluent软件对消声器内部速度流场、压力流场及湍动能的分布情况进行数值模拟分析。根据分析结果对消声器进行优化设计,以降低消声器内部的涡流强度,减少排气过程的压力损失。     

轮胎式压路机消声器的CFD模拟探究

首先采用计算流体动力学(CFD)软件数值模拟了某一算例消声器的内部流场,然后将软件数值模拟的结果与实验数据进行了比对,验证了该做法的可靠性.在此基础上,用同样的数值模拟计算方法研究某型号轮胎式压路机的消声器压力损失的影响,得到该压路机消声器的压力损失的影响规律,为该型号压路机的消声器结构设计和性能改进提供理论依据.     

结构因素对扩张式消声器压力损失影响

作为消声降噪的主要设备,排气消声器不仅要保证一定的消声性能,还要尽量减少压力损失。发动机的功率损失与压力损失息息相关,因此设计消声器时必须控制压力损失的大小。影响消声器压力损失的因素有很多,比如消声器结构、入口流速、温度等。利用计算流体力学方法分析消声器内部流场分布,探讨不同结构因素下压力损失的变化关系,对于消声器的设计开发具有指导意义。     

3t叉车消声器的设计

分析3t叉车抗性消声器的插入损失、压力损失和结构参数的影响,仿真研究消声器内部的流场和压强分布,分析造成压力损失过大的原因,对消声器的压力损失进行了预测,提出根据整车发动机参数对消声器进行设计的方法,使消声器压力损失、插入损失满足3t级叉车的要求。     

排气系统消声器流体动力学与气动噪声分析

针对某款发动机排气系统消声器建立其结构模型与内部流体域模型,,利用有限体积法对内部流场的压力损失,速度矢量,湍动能等参数进行分析。以CFD计算结果作为声场分析的边界条件,应用声学软件Virtual.Lab进行气动声学计算,分析各频率下主消声器气动噪声分布情况。提出结构优化设计建议。     

一种柴油机用复合式消声器的设计与实验研究

针对公司研发的一款铁路维护机械,设计了共振腔型带穿孔管的阻抗复合式消声器。首先进行抗性消声器设计,通过对中低频的噪声进行分析计算,得到消声管道直径、共振腔直径、穿孔管板厚、开孔直径、共振腔长度和开孔个数等关键参数。然后,通过在抗性消声器内增加阻性材料,便成为阻抗复合式消声器。最后,根据理论计算结果进行消声器模型设计和制造,并装车验证。实验结果表明,所设计的阻抗复合式消声器能在不同工况下有效降低发动机的排气噪声。     

基于CFD方法的旁支型消声器性能分析

基于计算流体力学方法,综合考虑声学和流体动力学特性,对旁支型消声器进行性能分析。运用一维CFD软件GT-power计算了两种旁支型消声器具有不同插入长度时的传递损失,并对其结果进行了对比分析;利用三维CFD软件FLUENT对其流场特性进行数值模拟,计算得到了各模型的压力损失曲线,并对其影响因素进行了分析,仿真还得到了消声器腔内流速和湍动能的分布,进一步分析了其流动特性,并结合声学性能和流体动力学特性得到两种较好的结构布置,从而为消声器的设计优化提供了依据。     

Reducing low-frequency vibration in hydraulic systems by means of Helmholtz resonators

Low-frequency damping systems for the pressure pulsations in a pipeline system are investigated in a mockup of the fourth loop of a nuclear power plant. The acoustic characteristics of Helmholtz resonators are calculated. Acoustic tests are conducted to reduce the vibration at the blade frequencies of the circulation pump. It is shown that the efficiency of such structures depends both on the accuracy with which the resonator eigenfrequencies are matched to the blade frequency of the vibration source and on the resonator location within the pipeline system.     

Size and acoustic optimization of Helmholtz resonators

Optimization of the size of Helmholtz resonators effectively reduces the hydrodynamic noise in pipeline fluids.     

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。     

Focusing ultrasonic waves in a 2-D covered channel above the periodic array of Helmholtz resonators

This paper presents the numerical simulation and experiments on focusing low-frequency ultrasonic waves in a 2-D covered channel above acoustic metamaterials composed of the periodic array of Helmholtz resonators, in which the refractive index can be in a negative value. The 2-D channel above the acoustic metamaterials is covered by a plate to limit the area affected by the negative refractive index metamaterials. Ultrasonic waves propagated in the 2-D covered channel are found to be highly dependent on input frequency and the designed Helmholtz resonator structure, where its negative refractive index causes the focusing phenomenon in this channel. From the numerical simulation and experiments, an amplitude focus spot is observed in the peak-to-peak of the time domain signal and frequency response at 125 kHz by mapping a pressure field in the 2-D covered channel. Different focal points with several input frequencies are also identified. Our research demonstrates the possibility of applying the designed lens based on acoustic metamaterials to improve the focusing effect in ultrasonic testing.     

Multi-tone noise elimination in a space-constrained room lined with hybrid sound absorbers using a particle swarm method

High noise levels can be harmful to workers and lead to psychological and physiological ailments. A broadband noise hybridized with multiple pure tones has a high peak value and is detrimental to human hearing in an enclosed machine room. To efficiently reduce the reverberant part of the peak noise level, interest in shape optimization of a Helmholtz resonator attached to the internal wall is coming to the forefront. Research on Helmholtz resonators in dealing with a pure tone has been well-addressed. However, the development of a hybrid sound absorber used in simultaneously reducing both the pure tone and the broadband noise is rare. Therefore, we propose two kinds of hybrid sound absorbers (sound absorber A: a piece of perforate plate + a piece of sound absorbing material + air space + a Helmholtz resonator; sound absorber B: a piece of perforate plate + a piece of sound absorbing material + air space + two Helmholtz resonators) used to deal with a broadband noise hybridized with multiple tones. Here, two case studies for dealing with broadband noise hybridized with one tone and two tones will be introduced. Moreover, a numerical assessment of a sound absorption coefficient and the best optimized design for two kinds of hybrid sound absorbers under a space-constrained situation will be performed. Consequently, a successful approach in eliminating a broadband noise hybridized with multiple tones by using an optimally shaped hybrid sound absorber as well as a particle swarm method within a constrained space has been demonstrated.     

谐振管内非线性驻波的间断Galerkin方法*

基于伪一维瞬态可压缩Navier-Stokes方程和理想气体状态方程,并结合保持强稳定性的三阶Runge-Kutta格式和斜率限制器技术,构建一种整体轴向谐振激励下求解变截面谐振管内非线性驻波的间断Galerkin方法。分别对直圆柱形、指数形以及圆锥形谐振管内的非线性驻波进行数值仿真计算,通过与现有数值仿真结果对比,验证了本方法的正确性,并重现了已有试验中非线性驻波压力波形中的第二峰值。在直圆柱形和指数形谐振管内研究间断Galerkin方法的两种网格加密方式对于不同形状下谐振管内非线性驻波仿真计算的数值精度、消除数值振荡和准确捕捉激波的不同作用,以及不同CFL数对于数值精度的影响。在指数形谐振管内,通过与有限体积法不同网格数目下的数值仿真结果和计算时间对比,验证了本方法具有耗时短、效率高以及计算精度高的优点。在圆锥形谐振管内,研究不同流速下谐振管内压力和速度波形的变化,并发现随着流速的增加,谐振管小端处的压力幅值增加,大端处速度幅值也随之增加且速度波形中会产生激波。通过间断Galerkin方法分析研究几种谐振管内非线性驻波的各种物理属性,为谐振管形状优化提供了重要参考,也为实现谐振管内非线性驻波的工程应用奠定了良好的基础。     

旋涡气流场的形成与分析

旋涡气流光整加工是以旋涡气流为载体，带动磨粒紧贴工件内孔表面作高速、强劲的“龙卷风”式的螺旋运动，实现内孔表面的光整加工。这种新工艺的关键技术是如何形成旋涡气流及研究气流速度和压力对加工效果的影响关系。为此，应用流体力学理论分析形成旋涡气流场的条件，研制了模拟实验用的旋涡头，研究气流速度和压力沿径向的分布规律，建立了相关的数学模型，为进一步研究和应用提供了理论依据。     

基于尺度自适应模拟的汽车天窗风振噪声特性分析

采用尺度自适应湍流模型对一个简易天窗进行数值模拟,通过与试验结果对比,验证数值计算方法的准确性。针对某轿车天窗风振噪声问题,进行不同来流速度条件下的数值模拟,模拟结果表明,轿车天窗风振噪声是声反馈和亥姆霍兹共振两种机制共同作用的结果。在发生亥姆霍兹共振时,通过对一个周期内天窗开口处涡运动对乘员耳旁处压力的影响分析,揭示天窗产生风振的压力特性。深入地研究剪切层失稳特性,对于最强的风振噪声,流向上和横向上速度的方均根值最大,表明亥姆霍兹共振加剧了剪切层里的扰动,产生的风振能量最高。在乘员舱发生亥姆霍兹共振的风速条件下,随着乘员人数的增加,风振噪声的峰值声压级有所降低,与之相关的频率变化很小。     

Numerical analysis of acoustic characteristics in gas turbine combustor with spatial non-homogeneity

Acoustic characteristics in an industrial gas-turbine combustor are numerically investigated by a linear acoustic analysis. Spatially non-homogeneous temperature field in the combustor is considered in the numerical calculation and the characteristics are analyzed in view of acoustic instability. Acoustic analyses are conducted in the combustors without and with acoustic resonator, which is one of the acoustic-damping devices or combustion stabilization devices. It has been reported that severe pressure fluctuation frequently occurs in the adopted combustor, and the measured signal of pressure oscillation is compared with the acoustic-pressure response from the numerical calculation. The numerical results are in good agreement with the measurement data. In this regard, the phenomenon of pressure fluctuation in the combustor could be caused by acoustic instability. From the numerical results for the combustor with present acoustic resonators installed, the acoustic effects of the resonators are analyzed in the viewpoints of both the frequency tuning and the damping capacity. It is found that the resonators with present specifications are not optimized and thus, the improved specification or design is required.     

Dynamic characteristics of an unsteady flow through a vortex tube

Dynamic flow characteristics of a counter-flow vortex tube is investigated using hot-wire and piezoelectric transducer (PZT) measurements. The experimental study is conducted over a range of cold air outlet ratios (Y=0.3, 0.5, 0.7, and 1.0) and inlet pressure 0.15 MPa. Temperatures are measured at the cold air outlet and along the vortex tube wall. Hot-wire is located at cold outlet and PZT is installed at inner vortex tube by mounting at throttle valve. The cold outlet temperature results show that the swirl flow of vortex tube is not axisymmetric. The hot-wire and PZT results show that there exist two distinct kinds of frequency, low frequency periodic fluctuations and high frequency periodic fluctuations. It is found that the low frequency fluctuation is consistent with the Helmholtz frequency and the high frequency fluctuation is strongly related with precession oscillation.