J. M. Novak

The Herschel–Quincke tube: A theoretical, computational, and experimental investigation

A general expression for the transmission loss characteristics of the Herschel–Quincke tube is developed. This relationship eliminates the restrictions on duct cross‐sectional area employed in earlier analytical studies. The attenuation of sound by this configuration is also studied computationally in terms of a nonlinear one‐dimensional finite‐difference model that solves the balance equations of mass, momentum, and internal energy, coupled with the ideal gas equation of state. Transmission loss predictions from both analytical and computational models are then shown to correlate well with experimental data acquired from an extended impedance tube setup.

Circular concentric Helmholtz resonators

The effect of specific cavity dimensions of circular concentric Helmholtz resonators is investigated theoretically, computationally, and experimentally. Three analytical models are employed in this study: (1) A two-dimensional model developed to account for the nonplanar wave propagation in both the neck and the cavity; (2) a one-dimensional solution developed for the limit of small cavity length-to-diameter ratio, l/d, representing a radial propagation in the cavity; and (3) a one-dimensional closed-form solution for configurations with large l/d ratios which considers purely axial wave propagation in the neck and the cavity. For low and high l/d, the resonance frequencies determined from the two-dimensional approach are shown to match the one-dimensional predictions. For cavity volumes with l/d>0.1, the resonance frequencies predicted by combining Ingard’s end correction with one-dimensional axial wave propagation are also shown to agree closely with the results of the two-dimensional model. The results...

A computational approach for flow–acoustic coupling in closed side branches

The quarter-wave resonator, which produces a narrow band of high acoustic attenuation at regularly spaced frequency intervals, is a common type of silencer used in ducts. The presence of mean flow in the main duct, however, is likely to promote an interaction between these acoustic resonances and the flow. The coupling for some discrete flow conditions leads to the production of both large wave amplitudes in the side branch and high noise levels in the main duct, thereby transforming the quarter-wave silencer into a noise generator. The present approach employs computational fluid dynamics (CFD) to model this complex interaction between the flow and acoustic resonances at low Mach number by solving the unsteady, turbulent, and compressible Navier-Stokes equations. Comparisons between the present computations and the experiments of Ziada [PVP-Vol. 258, ASME, 35-59 (1993)] for a system with two coaxial side branches show that the method is capable of reproducing the physics of the flow-acoustic coupling and predicting the flow conditions when the coupling occurs. The theory of Howe [IMA J. Appl. Math. 32, 187-209 (1984)] is then employed to determine the location and timing of the acoustic power production during a cycle.

Wave attenuation in catalytic converters: Reactive versus dissipative effects

Acoustic wave propagation and attenuation in catalytic converters are investigated in the present study. The relationships for wave propagation in a catalytic monolith are derived first and then coupled to the wave propagation in tapered ducts which are commonly placed at either end of the monolith. Analytical and finite element approaches are used to solve the resulting coupled system of equations. Theoretical predictions are then compared with the experimental results for two different (one circular and the other oval) catalyst configurations. The attenuation characteristics of the catalyst with and without the monolith are also investigated.

The effect of high-amplitude sound on the attenuation of perforated tube silencers

A time-domain computational approach is applied to investigate the behavior of perforated tube silencers at high sound levels. The one-dimensional computational technique employs a lumped parameter model for the perforate flows. The lumped parameter perforate model is based on time-invariant approximations for the equivalent length l(eq) and resistance R, consistent with the use of a nonlinear perforate impedance. Empirical expressions for l(eq) and R are developed experimentally using nondimensional scaling parameters. The model is applied to geometries representative of automotive resonators and multiple-duct mufflers. Conditions are simplified from those in an actual automotive system by considering single-frequency excitation and zero mean flow. Simulations with linear perforate behavior are compared to experimental data obtained with an extended impedance tube system. Simulations with nonlinear perforate behavior for one concentric tube resonator are compared to published experimental data.

Insertion loss of a helmholtz resonator in the intake system of internal combustion engines: an experimental and computational investigation

Abstract Wide open throttle dynamometer experiments are conducted on a firing 3.0L V6 engine with a narrow-band silencer (Helmholtz resonator) in the induction system. The effect of the silencer in the intake system is studied by performing the experiments both with and without the silencer in an intake pipe connected to a prototype intake manifold with no zip tube and air cleaner, while maintaining the overall length of the intake system. Instantaneous pressure data is acquired at key locations for a number of speeds over the operating range (1000–5000 rpm). The sound attenuation characteristics of the Helmholtz resonator are determined in terms of insertion loss. The results are presented in time-domain, as well as order-domain. The present study also describes an ongoing effort towards employing nonlinear fluid dynamic models in the time-domain for the prediction of acoustic and power performance of internal combustion engines. The model predictions compared to the experiments at a number of locations show reasonable agreement for the instantaneous pressure and sound pressure levels.

Experimental investigation of in-duct insertion loss of catalysts in internal combustion engines

Abstract Acoustic performance characteristics of catalysts in the exhaust system are important in the development of predictive tools for the breathing system of internal combustion engines. To understand the wave attenuation behavior of these elements with firing engines, dynamometer experiments are conducted on a 3.0L V-6 engine with two different exhaust systems: one with the catalysts on the cross-over pipe, and the other that replaces the catalysts with equal length straight pipes. The instantaneous crank-angle resolved pressure data are acquired at wide open throttle and 500 rpm intervals over the operating range of the engine (from 1000 to 5000 rpm) at various locations in both exhaust systems. The effect of the catalyst is then isolated and discussed in terms of insertion loss at critical locations in the exhaust system. The analysis is presented both in terms of time-domain and order-domain. The predictive capability of a finite-difference based time-domain nonlinear approach is also demonstrated as applied to large amplitude waves in the exhaust system of firing engines.

Prospects for implementation of thermoelectric generators as waste heat recovery systems in class 8 truck applications

With the rising cost of fuel and increasing demand for clean energy, solid-state thermoelectric (TE) devices are an attractive option for reducing fuel consumption and CO2 emissions. Although they are reliable energy converters, there are several barriers that have limited their implementation into wide market acceptance for automotive applications. These barriers include: the unsuitability of conventional thermoelectric materials for the automotive waste heat recovery temperature range; the rarity and toxicity of some otherwise suitable materials; and the limited ability to mass-manufacture thermoelectric devices from certain materials. One class of material that has demonstrated significant promise in the waste heat recovery temperature range is skutterudites. These materials have little toxicity, are relatively abundant, and have been investigated by NASA-JPL for the past twenty years as possible thermoelectric materials for space applications. In a recent collaboration between Michigan State University (MSU) and NASA-JPL, the first skutterudite-based 100 W thermoelectric generator (TEG) was constructed. In this paper, we will describe the efforts that have been directed towards: (a) enhancing the technology-readiness level of skutterudites to facilitate mass manufacturing similar to that of Bi2Te3, (b) optimizing skutterudites to improve thermal-to-electric conversion efficiencies for class 8 truck applications, and (c) describing how temperature cycling, oxidation, sublimation, and other barriers to wide market acceptance must be managed. To obtain the maximum performance from these devices, effective heat transfer systems need to be developed for integration of thermoelectric modules into practical generators. [DOI: 10.1115/1.4023097]

A Comparison of Modeled and Measured 3-D In-Cylinder Charge Motion Throughout the Displacement of a Four-Valve SI Engine

The flow inside a combustion engine is highly complex and varies significantly with small changes in the engine configuration. For a long time IC-engine researchers have tried to predict the major mean flow patterns inside close-to-production engine setups. During the last decades computational fluid dynamics (CFD) has significantly contributed to the engine development process. Hence, significant research has focussed on the comparison of modeled and measured flows in IC engines. However, according to the knowledge of the authors, this study is the first fully three-dimensional (3-D), modeling and measurement effort that has evaluated the vast majority of the displacement volume by using an identical engine geometry. With improved, non-intrusive, 3-D velocity measurement technology, the vast majority of the cylinder displacement was explored and compared with Star-CD modeling results at the same locations. The majority of the ensemble-averaged, 3-D velocity data exhibited similar flow patterns and tumble numbers within the center of the cylinder. Significant flow differences were observed in the outer regions, close to the cylinder walls, as well as in the level and shape of the turbulence during the intake stroke. The flow differences found in this study confirm the need for developments in computational and experimental methods.

A computational approach for flow‐acoustic coupling in deep cavities

The quarter wave resonator, which produces a narrow band of high acoustic attenuation at regularly spaced frequency intervals, is a common type of silencer used in ducting systems. The presence of mean flow, however, is likely to promote an interaction between these acoustic resonances and the flow. The coupling for some discrete flow conditions leads to the production of both large wave amplitudes in the side branch and high noise levels in the main duct. Thus, the quarter wave resonator may become a noise source rather than a silencer. The present approach uses computational fluid dynamics to determine both the mean flow and acoustic fields simultaneously by solving the unsteady, turbulent, and compressible Navier–Stokes equations. By coupling the interaction between the mean flow fluctuations and vortices with the acoustic field, this method is capable of determining when flow‐acoustic coupling occurs and how variations in the geometry and flow conditions influence the acoustic pressure amplitudes.