【作者】 胡效东；

【导师】 周以齐；

【作者基本信息】 山东大学 ， 机械电子工程， 2007， 博士

【摘要】 本论文用计算流体动力学(CFD)和试验法研究抗性消声器的流体动力学特性和消声特性。研究工作包括：抗性消声器的压力损失随消声器的结构参数和边界条件的变化规律；用试验法验证CFD法计算抗性消声器压力损失的有效性；用频谱分析法研究所设计的抗性消声器产品的消声特性，结合抗性消声器的流体动力学特性研究抗性消声器的综合性能。本论文主要目的是提供一个基于CFD仿真和试验相结合的抗性消声器整体结构设计方法，通过在设计中综合考虑流体动力学特性和声学特性提高抗性消声器的设计质量。抗性消声器是控制内燃机排气噪声的主要技术措施。大量柴油机汽车和工程机械应用，所带来的噪声问题已成为环境污染的重要问题之一，作为主要噪声源之一的排气噪声一直是降低柴油机噪声的研究重点。衡量抗性消声器的性能指标主要包括：插入损失、压力损失、装配性能、结构工艺性和使用寿命。插入损失就是在给定测点处安装消声器前后声压级之差，代表消声器的消声性能。压力损失代表发动机的功率损失比，就是在消声器工作过程中，输入管和输出管内的平均全压差。消声器的外形结构设计受到汽车或工程机械的安装尺寸的限制，在规定的安装空间限制下，消声器产品的内部结构应在良好加工工艺性的基础上，满足各项性能指标的设计要求。抗性消声器研究涉及声学、流体动力学、传热和机械设计等技术领域。声学性能一直是抗性消声器的研究重点，传统的消声器声学性能研究主要是基于一维声波理论的传递矩阵法，该方法适用于简单结构消声器，但不能有效的表达复杂的三维空间的声波传播。随着计算机软硬件的不断发展和相关算法的不断进步，消声器声学研究从单纯的传递矩阵算法逐渐发展到边界元法和有限元算法，使消声器声学方面的计算精度越来越高，特别是在计算声学出现之后，消声器声学特性分析也经历了从一维平面波到三维立体声波的计算过程，仿真结果也越来越趋向于实际抗性消声器的声学特点。传统的抗性消声器压力损失计算采用基于流体力学理论的半经验公式法。抗性消声器是由突然扩大和突然缩小结构组合而成的粗短腔，且流速较高，利用半经验公式法计算压力损失精度不高，对于穿孔类等复杂结构消声器的压力损失计算更为困难。计算流体力学的出现，提供了一个新的研究抗性消声器流体动力学方法，可以利用流体动力学的基本理论公式，采用有限体积法仿真分析消声器内部流体的动力学特性，得到消声器内部流体的动力学参数，求出消声器的压力损失。本论文主要目的是寻求在抗性消声器的设计阶段就能有效计算消声器压力损失的方法，和消声器的声学特性结合起来，为消声器的结构设计和优化提供帮助。本论文研究内容包括：消声器内流场几何建模、有限体积法网格划分、边界条件确定、求解算法选择、CFD仿真分析和数据后处理等完整的消声器流体动力学分析和压力损失计算过程。研究中采用结构化网格和非结构化网格相结合的方法对较复杂消声器进行划分，在保证计算精度的前提下，尽可能减小计算量，提高计算速度。通过对单腔消声器流场仿真，分析了消声器在入口流速不同时内部流场的特点。在流速比较低的时候，流体经过突然扩大和突然缩小结构后能够充分释放，此时用半经验公式法和CFD法计算消声器压力损失结果相差很小。随着流速增加，进入到消声器的流体没有经过充分释放就排出体外，此时半经验公式法不再适用于计算抗性消声器的压力损失。空气的密度和粘度等物理特性受温度影响比较大，研究结果表明：在相同的流速下，消声器的压力损失随温度的升高而减小。研究了单膨胀腔消声器的主要结构参数和边界条件对消声器压力损失的影响规律。其中研究的非穿孔管单腔消声器单元包括：无内插管单腔消声器、带内插管单腔消声器、无内插管偏置单腔消声器和带内插管偏置单腔消声器。这四种单腔消声器的压力损失均随着流速的升高而增大；无内插管单腔消声器和带内插管单腔消声器的压力损失还随着膨胀腔的长度而增加，内插管使消声器的压力损失减小；无内插管偏置消声器和带内插管偏置消声器的压力损失受膨胀腔的长度和有无内插管的影响程度比较小；其他条件相同时，输入／输出管偏置消声器的压力损失大于输入／输出管同轴消声器的压力损失。研究了两种非穿孔管双膨胀腔消声器中间挡板位置对压力损失的影响。对于内插管偏置双腔消声器和无内插管非偏置双腔消声器，中间挡板的位置对消声器的压力损失影响都比较小。双腔消声器的压力损失基本上等于两个相当结构的单腔消声器在相同边界条件下的压力损失之和。该研究结果，为以后多腔消声器的压力损失预测提供了依据。在多种形式的穿孔管消声器结构中，选择了两种具有代表性的直流穿孔管单腔和横流穿孔管单腔消声器进行了分析讨论。直流穿孔管消声器的压力损失随穿孔率、膨胀腔长度和入口流速的增加而增大，穿孔率越大压力损失的增加越缓慢。横流穿孔管消声器的压力损失随着穿孔率的增加而降低，当穿孔率小于下阈值时，压力损失随着穿孔率的降低急剧上升，当超过上阈值时，压力损失随穿孔率的增加缓慢降低，消声器设计时，穿孔率应该控制在两个阈值之间。在穿孔率相同的情况下，横流穿孔管消声器的膨胀腔越短，压力损失越大。穿孔管的穿孔直径对消声器压力损失的影响比较小，在消声器设计的时候可以仅考虑声学因素。横流穿孔管消声器的压力损失远大于非穿孔管消声器和直流穿孔管消声器。仿真结果还表明，穿孔管消声器的流体动力学特性强于非穿孔类消声器。在现有抗性消声器声学结论的基础上，结合对单腔消声器的流体动力学研究成果，设计了挖掘机抗性消声器产品和五种典型的抗性消声器结构。针对柴油机消声器工作温度高和流体速度快的特点，简化消声器的工作条件，确定了复合抗性消声器仿真的边界条件。通过建模、网格划分和仿真分析，求出消声器的流体动力学特性，并根据相关标准计算出消声器的压力损失。进行了消声器的流体动力学参数现场测试，主要测量消声器的输入／输出口的全压、静压和输入口流速。其中消声器的入口流速作为消声器CFD计算的边界条件，输入／输出口的全压和静压用来计算消声器的压力损失。通过试验和CFD仿真结果对比，验证了本文用仿真方法计算抗性消声器压力损失的有效性。进行了某挖掘机空载情况下的噪声信号采集，采集的噪声信号主要包括：柴油机壳体辐射噪声、柴油机排气噪声和抗性消声器的排出噪声；柴油机不同转速下的噪声源噪声和消声器排出噪声；所设计消声器和参考消声器产品的排出噪声。通过分析发动机壳体辐射噪声、柴油机排气噪声和消声器排出噪声的频谱特性，得出实际测量得到的抗性消声器排出噪声信号在某些频段消声效果不佳的原因是受柴油机壳体辐射噪声的干扰的结论。柴油机的排气噪声在不同转速时的频谱特性相似，排气噪声的强度随柴油机转速的加快而增大，抗性消声器的消声量也随柴油机转速的提高而增大。通过对比分析六种抗性消声器产品排出噪声的频谱特性和插入损失结果，得出结论：膨胀比影响消声器的消声效果，膨胀比越大，消声效果越好；穿孔管抗性消声器对柴油机排气噪声的中高频部分有比较好的消声性能。四腔穿孔管消声器高频的消声量大于三腔消声器，采用多个内插管代替单内插管有利于低频噪声的降低。穿孔率非常小的穿孔管对低频噪声的消除也比较有利；锥形内插管和圆柱形内插管相比，能改善中低频噪声的消声效果。结合前面的流体动力学特性，综合评价了六种抗性消声器的性能，证明所设计的抗性消声器具有良好的消声性能和流体动力学特性。本文用CFD法定量地研究了简单消声器的压力损失随消声器结构参数和边界条件的变化规律，结合已有的消声器声学研究结论，研究了基于CFD仿真和试验的抗性消声器设计方法，总结了相应的设计步骤：设计目标确定、消声器气流参数确定、结构初步设计、压力损失计算、消声器内部结构设计和试验验证等。并利用该方法针对某型号挖掘机进行了抗性消声器设计，试验表明所设计消声器具有良好的声学和流体动力学特性，得到企业的好评。更多还原

【Abstract】 The method of computational fluid dynamics (CFD) and test has been used to study the fluid dynamics and acoustic performances of resistance muffler. The main contents of this dissertation are shown as following: the changing regularities of pressure loss effected by the structure parameters and the boundary conditions for resistance muffler; validity certification of pressure loss computation with the method of CFD with pressure loss results comparison of CFD and test; muffling performance study with sound signal spectrum analysis of noise exhausted out of the diesel, sound radiated from the shell of the diesel and the noise exhausted out of mufflers. The main object of this dissertation is to explore a method for resistance muffler design based on CFD simulation and tests to improve the design quality integrated the performances of fluid dynamics and acoustics.Resistance muffler is the main device to attenuate the exhausted noise of internal-combustion engine presently. Noise pollution has become one of the important problems of environment pollution with the applications of automobile and construction machinery driven by diesel, and the exhausted noise has been paid attention to improve the integrated performance of diesel for a long time. The main performances of resistance muffler include insert loss, pressure loss, processing property of manufacture and operational life span. Insert loss represents the sound attenuation degree of muffler, which is the difference of sound pressure levels of exhaust noise at the positioned place with the muffler installed or not. Pressure loss reflects the power loss ratio of internal-combustion engine with the difference of the mean total pressure in the double pipes of input and output. The dimensions of muffler design should be limited in the demand of assembly with simple structure, and the operational life span is another factor with the muffler being one non-vulnerable part.Resistance muffler research relates with the fields of acoustics, fluid dynamics, heat transfer and mechanism design. Acoustic performance has been the most important property for muffler design depicted in literatures at presents. The method of transmission matrix based on 1-demensionsl plane wave theory is the traditional way to study the acoustical performance of resistance muffler, which has become mature for simple structure muffler with the deficiencies of low decision for complex muffler design as for perforated muffler. With the fast development of software and hardware of computer and the corresponding arithmetic improvment, acoustics simulation of resistance muffler has been becoming more and more actual. The acoustics simulations have experienced the developments based on 1-dimension, 2-dimension and 3-dimension, with the simulation results has becoming more and more approach to actual muffler.The half-experienced equations based on the theory of fluid dynamics have been used in the traditional way for pressure loss computation, which is not suitable for pressure loss computation of resistance muffler with the structure of pyknic type and fast fluid velocity in resistance muffler. The computational fluid dynamics (CFD) affords a new method for fluid dynamic simulation of resistance muffler which can be used to compute the fluid dynamics performances with the method of finite volume based on basic theory and the pressure loss can be calculated with the corresponding post data-processing. The main object of this dissertation is to explore an effective method for pressure loss computation during the procedure of muffler design, which can be used to study the performances of resistance muffler combined with the acoustic performance.The method of pressure loss computation with CFD simulation has been used with the procedure of modeling, meshing, boundary condition confirmed, arithmetic selection, simulation analysis and data post-processing. Structured jointed with unstructured grids have been used to mesh the complex resistance muffler, which can accelerate the computing velocity with the calculation reduction under the premise of precision confirmed.The pressure loss results calculated with the methods of half-experience equations and the CFD simulation have been proved to be the same with fluid flowing at low speed with the fluid can be released adequately. The former method is unsuitable when the flow speed increasing with the fluid pushed out of the muffler nonnaturally. Temperature should be considered during CFD simulation because it relates with the properties of air as density and viscidity. The pressure loss decreases with the fluid temperature increasing of input duct of muffler with the same fluid velocity.The regularities of pressure loss changing with structure parameters and boundary conditions have been achieved for single-chamber resistance muffler, four types of which are typical muffler, muffler with interpolated pipes, muffler with input/output offset and muffler with interpolated offset. Results have been obtained as following: Pressure loss of all the four types of muffler increases with the velocity of input flow increasing; Pressure loss of typical muffler and muffler with interpolated pipes rises with the chamber-length increasing, and the interpolated pipes makes the pressure loss decrease; Interpolated pipes and the chamber length affect pressure loss little for the input/output offset muffler; Pressure loss of input/output offset muffler is much bigger than pressure loss of muffler with input/output coaxial.Two types of double-chamber muffler have been studied to explore the effect of baffle position on the pressure loss computation, and the types of which are the interpolated pipes offset muffler and the input/output coaxial muffler without interpolated pipes. The baffle position affects pressure loss little for each double-chamber muffler. The pressure loss of the each double-chamber muffler is nearly the same as the pressure loss sum of two single-chamber muffler with equivalence structure and same boundary conditions, which afford a good method for pressure loss estimation of multi-chamber muffler during the procedure of muffler design.Straight-through and cross-flow perforated single-chamber mufflers have been selected to seek the relations of pressure loss changing with the main parameters and the boundary conditions, and the results obtained as following: Pressure loss of the straight-through perforated mufflers increases with the increase of all the porosity, chamber-length and the flow velocity of input; For the cross-flow perforated mufflers, pressure loss decreases with porosity increasing, pressure loss increases abruptly when the porosity is less than the low threshold value while it changes little when the porosity is greater than the high one. The porosity should be controlled between the two thresholds for effective muffler design; The diameters of the perforated holes for the cross-flow perforated mufflers effects the pressure loss little, and it can be negligible during muffler design; Pressure loss of the cross-flow perforated mufflers is much bigger than that of the straight-through mufflers and non-perforated muffler under the same boundary conditions. The dynamical property of perforated muffler is much better than the non-perforated one.One practical resistance muffler has been designed together with another five mufflers with typical structure for performance comparison based on the conclusion acoustics and fluid dynamics which has been achieved. The boundary conditions of the composite muffler have been confirmed with the simplified working conditions according to the practical working conditions of practical muffler for an appointed model number of excavator. The dynamical properties have been obtained with CFD simulation, and the pressure loss of composite has been solved based on the corresponded standard.Velocity and pressure at the appointed positions in the input/output pipes of muffler have been measured with the corresponding apparatus equipped. CFD has been proved to be an effective method for pressure loss computation with the results comparison of the CFD and test.The test equipment for noise measure has been made up of signal collection appliance, sound level meter and computer according to the practical operational position of resistance mufflers. The spectrums of sound level for radiated noise of diesel, noise exhausted out of diesel directly and muffler have been analyzed to research the noise property muffler, the corresponding results as following: the noise signal measured beside the output of muffler has been proved to be disturbed by the noise signal radiated from the shell of diesel and the noise signal of diesel accessories. The muffling rules of muffler changing with the speed of rotation have been studied with the spectrum analysis of noise signal exhausted out of muffler with different speed of diesel. The sound pressure level of noise increases with the diesel speed of rotation increase, but the signal spectrum properties of noise changes little with different speed of diesel rotation.Conclusions have been obtained with spectrums analysis of exhausted noise together with pressure loss computation of the six practical resistance mufflers as following: Expand ratio influences the effect of sound attenuation, and the expand ratio is bigger, the muffling is better; Interpolated pipes radial is available for noise muffling of low-frequency stage; Sound attenuation of intermediate and high frequency for four-chamber muffler is much better than three-chamber one with the same outline parameters. Multi-interpolated pipes used in the muffler have better muffling effect than single-interpolated pipes for low-frequency muffling. The low porosity for perforated muffler is not only useful for high frequency noise muffling, but also for low-frequency sound attenuation. The taper interpolated pipes can improve the muffling effect of low and intermediate frequency stage instead of column ones. The resistance muffler designed for an appointed evacuator has been validated with good performances both for noise attenuation and fluid dynamics.The method for resistance muffler design based on CFD simulation and test has been studied integrated with the conclusions of both acoustical and fluid dynamical in existence. The corresponding steps has been offered as objective confirmed of design, flow parameters confirmed for fluid in muffler, preliminary design of structure, pressure loss computation, structure design inside muffler and the test validity, which has been testified to be reasonable with a practical muffler design which has good performances of both muffling and fluid dynamics design in this method.更多还原