Measuring wave dynamics in IC engine intake systems

Wave dynamics in the intake system are known to strongly influence the performance of naturally aspirated internal combustion (IC) engines. Detailed measurements of the wave dynamics are required to optimize the performance of an engine, to validate the results of an engine performance simulation or to better understand the physics of the intake system. Five different methods for making such measurements are discussed in this paper. Four are based on different forms of pressure measurement and one uses hot-wire anemometry. The different methods are investigated by using results obtained on a single cylinder research engine. The different methods are used to produce measurements of fluctuating pressure and velocity as well as the specific acoustic impedance ratio of the intake pipe. Both time and frequency domain results are considered. The conclusion is that no single method is perfect or indeed universally applicable to all situations and in a typical investigation of wave action more than one method is likely to be used. The combined use of two methods, wave decomposition and an unusual bi-directional pitot-static tube, seems to offer a robust reliable and useful strategy for measuring wave dynamics in the intake pipe that should prove successful on most IC engines.     

低压离心压缩系统喘振发生过程的实验观察

在一离心压缩系统喘振实验台上，通过系统各位置及沿叶轮出口圆周上压力波动进行的动态测量，对进入及退出瑞振时的瞬态特性进行了实验观察．实验发现系统的喘振首先发生在储气容腔内，并由下游向上游发展，在此过程中喘振幅度从容腔至进口管呈减小的趋势，且发生时间也逐渐落后．此外，还对喘振的形成和退出过程及其相应特性也进行了观察．     

轻卡进气管的结构优化及其声学性能

为有效降低轻卡进气管的噪声，首先通过原始进气管的噪声实验，测试得出噪声的主要贡献频率，结合管道的布置情况，进行了消声器(谐振腔)的设计，进而完成对进气管的优化设计；通过专业声学分析软件LMS Virtual.lab对优化前后的进气管进行声学性能的模拟研究，得出了谐振腔对声场的具体影响；通过噪声实验，分析出加装谐振腔的进气管相比于原始进气管的降噪效果。研究结果表明：在所研究的进气管噪声的主要贡献频率下(即125 Hz、180 Hz、465 Hz、640 Hz)，加装谐振腔后，传递损失均能得到有效增加；在怠速工况和加速工况下，优化后的进气管噪声值均能满足限定值。因此，通过添加谐振腔来优化进气管可以达到了较好的降噪效果。该研究可为汽车进气管降噪元件的优化设计提供一定的指导。     

Time domain identification of standing wave parameters in gas piping systems

A method for experimentally determining the natural frequencies and modal pressures of an air or gas piping system is presented. Such information is of interest in installations where pressure pulsations caused by pumps or compressors are of importance. In the method a time domain based technique is used which was originally developed as an alternative to frequency response methods for determining the vibration parameters (natural frequencies, modes, damping factors) of structures, to avoid difficulties often encountered in interpreting complex and non-conclusive frequency response data such as arises from systems having numerous modes, some of which may be highly damped or closely spaced in frequency. In this application, a straight steel pipe with a sound source at one end and closed at the other end was used. Two microphones were used to measure the pressure at two locations in the pipe. The free pressure response following a rapidly swept sinewave input was recorded, digitized and then used in a computational procedure based on a lumped parameter representation of the system. The natural frequencies and the corresponding modal pressure ratios at the two stations, thus obtained, are compared with mention here that although in the experiment reported here an external frequency sweep excitation was used, the technique works as well with free decay response after a system shut-off, impulse response or random responses from normal system operation.     

Sound radiation from a water-filled pipe,radiation into light fluid

This paper is concerned with the sound radiation from a water-filled exhaust pipe. The pipe opening and a plate attached to it form a vibrating surface for this radiation. Fluid-structural coupling between the pipe and enclosed fluid is included in the system modeling, but light fluid assumption is used for sound radiation into the space above the vibrating surface. In this paper, a numerical study on the n = 0 mode in the pipe shows that the wave types associated with this mode have different characteristics in two regions of the nondimensional frequency omega. In the first region of 0相似文献   

空调水系统的压力分析及定压点的选择

根据伯努利方程分析讨论了空调水系统采用膨胀水箱定压时,定压点选在回水管最高点和循环水泵吸入口位置对水系统压力分布的影响,该分析对于系统的安全运行提供了充足的理论依据。     

Acoustical analysis of pipes with flow using invariant field functions

An analysis of the pressure field within a pipe is carried out using simplified formulations of pipe acoustics. The fluid contained within the pipe is considered non-viscous, while the flow velocity of the fluid is assumed to be smaller than the speed of sound.The analysis is limited to frequencies which are well below the pipe ring frequency, i.e., at which only simple waves can propagate. Expressions and diagrams are given which specify the applicable frequency range in each particular case.Three invariant functions of the internal pressure field are evaluated. These functions allow for the determination of the following quantities: base pressure spectrum (spatial mean r.m.s. value), lower and upper bounds of the pressure spectrum for the entire pipe, pressure spectrum at an arbitrary position, speed of sound in the contained fluid and fluid flow velocity.Experimental identification of these quantities requires simultaneous measurement at three points. A few measurements carried out on one air-filled and one water-filled pipe have demonstrated the potential of pipe invariant functions for acoustical analysis.     

浅埋三舱管廊甲烷爆炸的地面响应规律

地下综合管廊可燃性气体爆炸事故时有发生,给地面人员的生命和财产造成了巨大损失。依托重庆市某地下综合管廊试点工程,基于物质点法,采用点火增长模型模拟浅埋管廊泄漏甲烷气体爆炸冲击管廊本体结构和围岩的过程,研究爆炸作用下地面压强与位移的响应特性。研究发现:泄爆作用下管廊及围岩会出现因接触面反射和折射产生的次生应力波,管廊横向方向次生波振幅随距起爆点水平距离的增大而增大,而管廊纵向方向产生的次生波振幅较小,且随距离增大变化较小;爆炸作用造成整体地面沉降,但在起爆点中心附近地面隆起,这种隆起由管廊本体结构破裂,气体直接冲击岩土体形成的剧烈隆起和管廊整体震动形成的轻微隆起两部分组成。     

应用光纤布喇格光栅传感器监测地下管道腐蚀的新方法研究

地下管线工作环境恶劣,腐蚀是引起它破坏和失效的主要原因之一.本文提出了一种应用光纤光栅传感器监测管道腐蚀的新方法.输送石油和天然气等一些物质的管道内部存在的压力会使管道发生膨胀,进而导致管道外壁产生环向变形.假定管道为无限长,管道内部压力导致的管道外壁轴向应变可忽略不计,当管线发生腐蚀时,会导致管壁变薄,管道内部的压力又可以看作基本不变,这样就会增大管道外壁的环向应变.当管道内部压力保持恒定时,管道壁厚与应变之间存在一定的反比例关系,本文方法就是将封装好的光纤光栅传感器粘贴在管道外壁,通过监测外壁环向变形来判断管道腐蚀的情况和程度.通过理论值、模拟值和试验值三者的对比分析来说明了这种新方法是可行的,并且值得被广泛应用,为埋地管道的防灾减灾提供了一种对策.     

油气水三相流中的复杂相态及压力降研究

将水平管划分为三个测量段,以空气、水和高粘度油体为工质,研究了油气水三相流中由流动引起的液－液复杂相态及其所对应的三相流压力降。试验研究发现,油气水三相流在三个测量段中可由流动引起不同的液－液相态,致使对应于相同的油、气、水三相体积通量,三相流阻力损失存在多值性。对不同的液－液相态建立了与之适应的阻力损失计算模型,模型预测结果与试验结果吻合     

A study of vibroacoustic coupling between a pump and attached water-filled pipes

This paper presents a model for the vibroacoustical behavior of a pump coupled with water-filled pipes. Coupling between (a) the pump and the inlet and outlet pipes, and (b) the pipe wall and the fluid contained in the pipe, is investigated through analytical modeling and numerical simulation. In the model, the pump is represented by a rigid body supported by multiple elastic mounts, and the inlet and outlet pipes by two semi-infinite water-filled pipes. The vibration characteristics of the coupled system under the excitation of mechanical forces and fluid-borne forces at the pump are calculated. The results enhance our understanding about how the input mechanical and fluid excitation energy at the pump is transmitted to the pipes and how to relate the piping vibroacoustical response to the excitations at the pump. This study assists in predicting dynamic stress in pipes for given excitations at the pump, and in developing methods to identify the nature (fluid or mechanical) of the excitation forces at the pump using the vibration and dynamic pressure measurements on the pump/pipe system.     

Theoretical and Experimental Investigation of Flexural Vibration Transfer Properties of High-Pressure Periodic Pipe

According to the theory of phononic crystals,the hydraulic pipeline is designed to be a periodic structure composed of steel pipes and hoses to suppress the vibration of the hydraulic system with band gaps.We present theoretical and experimental investigations into the flexural vibration transfer properties of a high-pressure periodic pipe with the force on the inner pipe wall by oil pressure taken into consideration.The results show that the vibration attenuation of periodic pipe decreases along with the elevation of working pressure for the hydraulic system,and the band gaps in low frequency ranges move towards high frequency ranges.The periodic pipe has good vibration attenuation performance in the frequency range below 1000 Hz and the vibration of the hydrauhc system is effectively suppressed.All the results are validated by experiment.The experimental results show a good agreement with the numerical calculations,thus the flexural vibration transfer properties of the highpressure periodic pipe can be precisely calculated by taking the Quid structure interaction between the pipe and oil into consideration.This study provides an effective way for the vibration control of the hydraulic system.     

Reduction of noise on large size pipes by inserting acoustic grilles

This paper deals with the problem of silencing relatively large intake pipes by inserting reactive and dissipative absorption sections inside the end of the pipe with a cascade arrangement to form an acoustic grille.Experiments have been carried out on various internal configurations of the same type of section for silencing intake pipes.This paper describes the application of an acoustic grille for silencing the intake end of an engine cooling pipe on a FIAT IVECO'bus. Experimental results have shown a noise attenuation of about 5 dB(A) on that specific source.     

Acoustic impedance at the interface between a plain and a perforated pipe

This paper considers the effective impedance that pertains as low frequency sound in a plain pipe radiates into a general perforated pipe of equal diameter. A previous theory that considered only the reactance is extended to also include resistance. Experimental measurements are made of the response of a Helmholtz resonator to an external sound field, where the neck of the Helmholtz resonator has both plain and perforated pipe sections. A complete theoretical model of this resonator allows for comparison between measured and predicted results of transfer functions from the external to internal sound fields of the resonator. The Nyquist plot of the admittance transfer function is extremely sensitive to the small resistance values, whereas the pressure transfer function gives more accurate results for resonant frequency and hence reactance than the usual method. In particular the results for resistance are so sensitive that it becomes possible to infer which of the current models for aperture resistance within the perforate is the most appropriate.     

ITER气体注入系统汇集管道现场安装阶段的检漏方案

根据ITER设计真空手册泄漏检测的要求,提出了ITER气体注入系统汇集管道在现场安装阶段的检漏方案。对汇集管道内管的检漏采用真空氦喷吹法进行,按照窗口小室的焊接顺序,每完成一个窗口小室内的焊接就进行一次检漏。对内管检漏所需要的最长抽气时间和最长反应时间进行了评估。结果表明,单次检漏的抽气时间在30min以内,检漏的反应时间在10min以内。对汇集管道包容管的检漏采用正压氦吸枪法进行,在包容管所有焊接均完成后一次性进行检漏。     

Reflex activation of laryngeal muscles by sudden induced subglottal pressure changes.

In measuring the effect of subglottal pressure changes on fundamental frequency (Fo) of phonation, the effects of changing laryngeal muscle activity must be eliminated. Several investigators have used a strategy in which pulsatile increases of subglottal pressure are induced by pushing on the chest or abdomen of a phonating subject. Fundamental frequency is then correlated with subglottal pressure changes during an interval before laryngeal response is assumed to occur. The present study was undertaken to repeat such an experiment while monitoring electromyographic (EMG) activity of some laryngeal muscles, to discover empirically the latency of the laryngeal response. The results showed a consistent response to each push, with a latency of about 30 ms. Despite this response, analyses of fundamental frequency versus subglottal pressure changes during the interval of constant EMG activity were in general agreement with previously published values. With respect to the nature of the electromyographic response itself, its timing was found to be within the range of latencies appropriate for peripheral feedback, and was also similar to that for an acoustically--or tactually--elicited startle reflex.     

Wave propagation and vibration response of a periodically supported pipe conveying fluid

Propagation of free harmonic waves, in a periodically supported infinite pipe, has been studied. The presence of the Coriolis term in the equation of motion renders the phase velocity different for the positive and the negative going waves. Hence no classical normal modes (in the sense of standing modes) exist. Natural frequencies of a periodically supported finite pipe have been obtained by using the wave approach. The response of the infinite pipe to a convected harmonic pressure field has also been obtained. Owing to the difference in the phase velocities of the positive and the negative going free waves, the coincidence frequency depends on the direction of the convected loading. The static buckling or the divergence instability of such pipes has also been considered from the wave approach.     

Entropy Generation for Negative Frictional Pressure Drop in Vertical Slug and Churn Flows

It is widely accepted that the frictional pressure drop is impossible to be negative for pipe flow. However, the negative frictional pressure drops were observed for some cases of two-phase slug and churn flows in pipes, challenging the general sense of thermodynamic irreversibility. In order to solve this puzzling problem, theoretical investigations were performed for the entropy generation in slug and churn flows. It is found that the frictional pressure drop along with a buoyancy-like term contributes to the entropy generation due to mechanical energy loss for steady, incompressible slug and churn flows in vertical and inclined pipes. Experiments were conducted in a vertical pipe with diameter as 0.04 m for slug and churn flows. Most of the experimental data obtained for frictional pressure drop are negative at high gas–liquid ratios from 100 to 10,000. Entropy generation rates were calculated from experimental data. The results show that the buoyancy-like term is positive and responsible for a major part of entropy generation rate while the frictional pressure drop is responsible for a little part of entropy generation rate, because of which the overall entropy generation due to mechanical energy loss is still positive even if the frictional pressure drop is negative in vertical slug and churn flows. It is clear that the negative frictional pressure drops observed in slug and churn flows are not against the thermodynamics irreversibility.     

Windowless transition between atmospheric pressure and high vacuum via differential pumping for synchrotron radiation applications

A differential pump assembly is introduced which can provide a windowless transition between the full atmospheric pressure of an in‐air sample environment and the high‐vacuum region of a synchrotron radiation beamline, while providing a clear aperture of approximately 1 mm to pass through the X‐ray beam from a modern third‐generation synchrotron radiation source. This novel pump assembly is meant to be used as a substitute for an exit vacuum window on synchrotron beamlines, where the existence of such a window would negatively impact the coherent nature of the X‐ray beam or would introduce parasitic scattering, distorting weak scattering signals from samples under study. It is found that the length of beam pipe necessary to reduce atmospheric pressure to below 10 mbar is only about 130 mm, making the expected photon transmission for hard X‐rays through this pipe competitive with that of a regular Be beamline window. This result is due to turbulent flow dominating the first pumping stage, providing a mechanism of strong gas conductance limitation, which is further enhanced by introducing artificial surface roughness in the pipe. Successive reduction of pressure through the transitional flow regime into the high‐vacuum region is accomplished over a length of several meters, using beam pipes of increasing diameter. While the pump assembly has not been tested with X‐rays, possible applications are discussed in the context of coherent and small‐angle scattering.     

Analysis of pipeline networks using two-ports

Majority of vibration problems arise in pipeline networks are attributed to the high-pressure pulsations. Pulsations are generated by fluid machines such as compressors and pumps. These pulsations turn into shaking forces at elements such as pipe bends and pipe reducers, which in turn excite vibrations in the connected piping network. High vibrations beyond the endurance limit of the pipe material may cause damage to pipes, supports, and equipment. In addition, if the source pulsation frequency coincides with one of the natural frequencies of the piping network, resonance will take place and the vibrations will be magnified to a large scale. Obviously, if these vibrations are not well controlled, they might cause damage to the whole system and foundation, and might lead to substantial financial losses. Thus, prediction of pulsations is important for safe and proper operation. In this paper, a pilot plant equipped with a reciprocating compressor, pipes, bends, and terminated by a vessel is built. The network is modeled using the two-port theory that splits the network into several cascaded elements, and predicts the response of the network. The prediction model uses the measured compressor source data as an input, which is determined by the indirect multi-load method that is usually used to characterize internal combustion engines. A pulsation suppression device is designed, modeled, manufactured and inserted into the pilot network. The pressure pulsations are measured with and without the pulsation suppression device, and compared to the predictions using the two-port theory.