燃烧室结构-声耦合特性研究

声振耦合影响燃烧室燃烧稳定性,加剧火焰筒薄壁结构疲劳破坏,声振耦合特性研究对燃烧室燃烧稳定性设计与结构抗疲劳设计非常必要。利用有限元软件建立燃烧室结构-声三维模型,进行燃烧室封闭结构声振耦合特性研究,计算出结构的固有频率和模态振型。通过试验,测量燃烧室声振传递函数,得到燃烧室结构声振耦合固有频率和模态振型。研究表明,声场相当于给结构增加了附加质量,降低了结构固有频率,并产生了特殊的耦合频率。试验验证了有限元计算结果的正确性,从而为燃烧室薄壁结构设计提供了参考。     

提取内燃机燃烧压力高频成分进行压力高频振荡研究

研究内燃机缸内压力高频振荡的机理以及压力高频振荡对燃烧噪声的影响。利用小波分析技术确定缸内压力高频振荡出现的范围,从而确定了燃烧室空腔声模态模型的对应曲轴转角范围。用声响应法和有限元法分别测量和计算不同曲轴转角下燃烧室空腔声模态,并对测量值和计算值对应曲轴转角进行了温度修正,模态试验结果与有限元计算结果较吻合。并对测量的缸内燃烧压力信号和噪声信号进行了分析。研究结果表明：缸内燃烧压力高频振荡是燃烧室的多阶共振频率受到激励引起共振的结果,燃烧压力高频振荡是影响燃烧噪声的重要因素。     

车内空腔声学模态试验与仿真分析

以某中型商用车为研究对象,基于LMSTest．Lab模态分析系统对车内空腔进行了声学模态试验与分析,获取了声学模态频率和模态振型,将声学模态与结构模态频率作对比,可以避开关键频率的声固耦合,减少低频噪声,同时建立该车空腔的有限元模型,进行了声学模态的仿真计算,为车内噪声的研究提供了参考,对改善其车内声学特性具有一定的指导意义。     

基于MATV技术的某减速器壳体声辐射研究

应用有限元方法对某减速器壳体进行了模态计算和振动响应计算,然后基于模态声传递向量(Model acoustic transfer vector,MATV)技术,计算得到减速器壳体的辐射声功率、壳体表面空气振动速度分布、外场声压级分布以及外场场点声压级等声学响应,展示了模态声传递向量技术在减速器声辐射预测中的应用方法和途径。通过对壳体对模态声学贡献量进行分析,确定了通过结构优化降低声辐射的方法。同时,壳体表面空气振动速度分布为粘贴阻尼材料降低减速器壳体声辐射提供了重要参考。     

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.     

通过声辐射模态计算矩形薄板的模态辐射效率

模态辐射效率是评价振动结构声辐射能力的一项重要指标。结构振动引起的声辐射问题是声学中一个长期的研究课题。评价振动结构的声辐射能力的一项重要指标就是模态辐射效率。通过声辐射模态理论,推导了任意边界条件下矩形薄板模态辐射效率的计算方法,通过计算方法可以直接得到模态辐射效率的数值解,而不需要进行数值积分。最后,以四边简支、四边固定、对边简支和对边固定、三边固定和一边自由矩形板为例,进行数值计算和分析。通过与前人的计算结果比较,验证了方法的有效性。     

高阶声模态对扩张室消声器声学性能的影响研究

由于煤矿风井截面很大,导致频率很低时风井消声器内部便激发了高阶声模态,消声器声学性能被大大影响.为改善消声器声学性能,利用管道声模态理论,对模态波激发频率和模态声压节线位置分布进行了分析和计算,对扩张室消声器进行了结构改进并利用LMS Virtual.Lab软件进行了声学仿真分析.为保证消声器的空气动力性能,又利用Fluent软件对消声器进行了流场仿真分析并进行了相应的结构优化.结果表明,经过结构优化的并联偏置消声器,可以在保持良好空气动力性能的同时,使消声器在低频段彻底摆脱高阶声模态带来的不利影响.     

Rijke管热声振荡声学特性数值模拟

为了探究热声振荡发生的因素及机理,建立了Rijke管热声模型,采用稳定有限元方法对频域线性欧拉方程进行数值求解,在考虑平均流速及火焰处温度梯度的情况下,分析了火焰热释放、平均流速和燃烧响应模型对Rijke管声学特性的影响.结果表明,火焰热释放对Rijke管纵向模态的本征频率影响显著,本征频率随火焰热释放的提高而增大;平...     

有源声学结构次级声源的布放规律研究

有源声学结构是近年来提出的一种控制结构低频声辐射的有效方案,它是智能结构在有源噪声控制领域的具体应用。次级声源的优化布放是有源声学结构研究中的核心问题,本文对此进行了研究。首先建立了有源声学结构的计算模型,然后基于声辐射模态和结构振动模态理论,推导总结出各种情况下次级声源的最优布放规律,最后用一系列的计算机仿真实例对该规律进行了验证。     

某型燃机燃烧室的数值模拟

燃料喷嘴双级径向旋流器在燃烧室内形成稳定的回流漩涡结构,有助于燃烧室火焰稳定和提高燃烧效率。文中建立了计算模型,利用CFX软件进行燃烧室的燃烧模拟,研究了燃烧室中流场分布、NO含量分布、温度场分布、燃料分布。模拟计算表明,此燃烧室具有较好的气动特性、稳燃性能与冷却性能,能够在额定工况下长时间稳定工作。     

Effects of various baffle designs on acoustic characteristics in combustion chamber of liquid rocket engine

Effects of various baffle designs on acoustic characteristics in combustion chamber are numerically investigated by adopting linear acoustic analysis. A hub-blade configuration with five blades is selected as a candidate baffle and five variants of baffles with various specifications are designed depending on baffle height and hub position. As damping parameters, natural-frequency shift and damping factor are considered and the damping capacity of various baffle designs is evaluated. Increase in baffle height results in more damping capacity and the hub position affects appreciably the damping of the first radial resonant mode. Depending on baffle height, two close resonant modes could be overlapped and thereby the damping factor for one resonant mode is increased exceedingly. The present procedure based on acoustic analysis is expected to be a useful tool to predict acoustic field in combustion chamber and to design the passive control devices such as baffle and acoustic resonator.     

Experimental study of acoustic damping induced by gas-liquid scheme injectors in a combustion chamber

In a liquid rocket engine, acoustic damping induced by gas-liquid scheme injectors is studied experimentally for combustion stability by adopting linear acoustic test. In the previous work, it has been found that gas-liquid scheme injector can play a significant role in acoustic damping or absorption when it is tuned finely. Based on this finding, acoustic-damping characteristics of multi-injectors are intensively investigated. From the experimental data, it is found that acoustic oscillations are almost damped out by multi-injectors when they have the tuning length proposed in the previous study. The length corresponds to a half wavelength of the first longitudinal overtone mode traveling inside the injector with the acoustic frequency intended for damping in the chamber. But, new injector-coupled acoustic modes show up in the chamber with the injectors of the tuning length although the target mode is nearly damped out. And, appreciable frequency shift is always observed except for the case of the worst tuned injector. Accordingly, it is proposed that the tuning length is adjusted to have the shorter length than a half wavelength when these phenomena are considered.     

Calculation on cylinder pressure fluctuation by using the wave equation in KIVA program

Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and knock.The current studies are based on cylinder pressure test to obtain ...     

燃烧室结构对天然气转子发动机燃烧过程的影响

以一台由端面进气汽油转子发动机改装而来的预混天然气转子发动机为研究对象,在FLUENT软件的基础上通过编程实现转子发动机三维网格的偏心运动,并选择合适的湍流模型、燃烧模型以及详细的CHEMKIN化学反应机理,建立基于化学反应动力学的端面进气天然气转子发动机三维动态数值模拟模型。通过与试验数据进行对比和分析,验证模型的可靠性。在此基础上,研究燃烧室结构对端面进气天然气转子发动机的缸内流场、温度场和中间产物浓度场的影响。结果表明,当燃烧室凹坑布置于转子曲面长度方向的前端和转子曲面宽度方向的中心时,燃烧过程同时利用了燃烧室后部的滚流以及燃烧室中部高速流区对火焰的加速作用,缸内整体燃烧速率最大。同时,其缸内压力最大以及中间产物OH的生成量也最大,其压力峰值比中置凹坑燃烧室提高了19.9%,但其NO质量分数仍在0.5%以内。     

Investigation of self-excited combustion instabilities in two different combustion systems

The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around 300Hz are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited high frequency instability has strong nonlinear characteristics.     

Experimental study of the role of gas-liquid scheme injector as an acoustic resonator in a combustion chamber

In a liquid rocket engine, the role of gas-liquid scheme injector as an acoustic resonator or absorber is studied experimentally for combustion stability by adopting linear acoustic test. The acoustic-pressure signals or responses from the chamber are monitored by acoustic amplitude. Acoustic behavior in a rocket combustor with a single injector is investigated and the acoustic-damping effect of the injector is evaluated for cold condition by the quantitative parameter of damping factor as a function of injector length. From the experimental data, it is found that the injector can play a significant role in acoustic damping when it is tuned finely. The optimum tuning-length of the injector to maximize the damping capacity is near half of a full wavelength of the first longitudinal overtone mode traveling in the injector with the acoustic frequency intended for damping in the chamber. When the injector has large diameter, the phenomenon of the mode split is observed near the optimum injector length and thereby, the acoustic-damping effect of the tuned injectors can be degraded.     

Combustion characteristics of anthracite in a vertical cyclone combustor

Isothermal, gas combustion and coal tests were undertaken in order to characterise a vertical cyclone combustor for burning anthracite. Inert particles (alumina cement) were used during the first two series of tests, in order to characterise chamber temperatures, material collection efficiencies and size distribution of particles. Mixture ratios from 0.4 up to 1.6 were tested in steps of 0.2. Under isothermal conditions, an optimum penetration length of vortex finder into the combustion chamber was found to be approximately 10% of the chamber length. The highest temperature can be obtained in the lower section of the combustion chamber both in gas and in coal combustion. The collection efficiency of the cyclone combustor in the various modes of operation was found to be excellent. For coal tests, mixed firing with coal and gas was adopted to sustain the flame in the combustor. The mixed fuels investigated here contain 60, 70 and 80% by mass of coal, and the 70% case was found favorable in the context of carbon burnout and collection efficiency.     

基于光学测量的发动机燃烧室容积反求研究

以汽车发动机缸盖燃烧室容积的测量为研究对象,复制了缸盖燃烧室的硅胶模型。应用三维光学测量技术对燃烧室硅胶模型进行扫描测量,以获取燃烧室模型的点云数据。利用反求工程技术进行燃烧室模型重构,获得燃烧室的CAD模型。运用UG软件的体积计算功能计算燃烧室CAD模型的体积,得到缸盖燃烧室体积(容积)数据。同时,可将燃烧室CAD模型存档备用,为燃烧室的再设计、再制造或再维修提供参考。