Phased microphone arrays have become a well-established tool for performing aeroacoustic measurements in wind tunnels (both open-jet and closed-section), flying aircraft, and engine test beds. This paper provides a review of the most well-known and state-of-the-art acoustic imaging methods and recommendations on when to use them. Several exemplary results showing the performance of most methods in aeroacoustic applications are included. This manuscript provides a general introduction to aeroacoustic measurements for non-experienced microphone-array users as well as a broad overview for general aeroacoustic experts.

/pdf/a-review-of-acoustic-imaging-methods-using-phased-microphone-3wlj7tlfgu.pdf

A review of acoustic imaging methods using phased microphone arrays

This article reviews Handbook of Noise and Vibration Control by Malcolm J. Crocker , New Jersey, 2007 1584 pp. Price: $195.00 (hardcover) ISBN: 0471395994

Handbook of Noise and Vibration Control.

An object of the invention is to provide an exhaust emission control device which eliminates the use of a heat-retention structure using heat-insulating material such as glass wool so as to attain substantial lessening in production cost. A discharge end of a gas gathering chamber is connected to an entry end of a mixing pipe so as to encase the entry end of the mixing pipe and close an opened end face in a required spaced-apart relationship. Moreover, a side surface of the entry end of the mixing pipe adjacent to the discharge side of the particulate filter is formed with an opening; and gas guide passages are formed in the gas gathering chamber by guide fins for tangential introduction of all of the exhaust gas from the discharge side of the particulate filter to the opening. An extra space isolated from the gas guide passages is ensured in the gas gathering chamber as a heat-retention chamber surrounding the entry end of the mixing pipe.

Exhaust emission control device

Acoustic wave propagation in flow ducts is commonly modeled with time-domain non-linear Navier–Stokes equation methodologies. To reduce computational effort, investigations of a linearized approach in frequency domain are carried out. Calculations of sound wave propagation in a straight duct are presented with an orifice plate and a mean flow present. Results of transmission and reflections at the orifice are presented on a two-port scattering matrix form and are compared to measurements with good agreement. The wave propagation is modeled with a frequency domain linearized Navier–Stokes equation methodology. This methodology is found to be efficient for cases where the acoustic field does not alter the mean flow field, i.e., when whistling does not occur.

A frequency domain linearized Navier-Stokes equations approach to acoustic propagation in flow ducts with sharp edges.

Experimental investigation on combustion, noise, vibrations, performance and emissions characteristics of diesel/n-butanol blends driven genset engine

Sound and vibration

The point-matching method on dissipative silencers of arbitrary cross-section

Both linear (frequency domain) and non-linear (time domain) prediction codes are used for the simulation of duct acoustics in exhaust systems. Each approach has its own set of advantages and disadvantages. One disadvantage of the linear method is that information about the engine as an acoustic source is needed in order to calculate the insertion loss of mufflers or the level of radiated sound. The source model used in the low frequency plane wave range is the linear time invariant 1-port model. This source characterization data is usually obtained from experimental tests where multi-load methods and especially the two-load method are most commonly used. These measurements are time consuming and expensive. However, this data can also be extracted from an existing 1-D non-linear CFD code describing the engine gas exchange process. The pressure and velocity predictions from two acoustic load cases can be used to determine the source strength and impedance at a particular location in the exhaust line. This has been done at a location downstream of the turbocharger in the exhaust system of a heavy diesel truck over a number of speeds and engine loads. This source data is then used in a linear simulation of the exhaust line to predict sound pressure levels at a free field microphone position. The predicted source data and sound output at the microphone position is validated against measured data. The results show that you can obtain reasonably accurate source data and approximate free field sound pressure level predictions using non linear simulation in a linear acoustic model of the exhaust system. This technique can be used to extend the use of linear acoustic simulations to models of the complete exhaust line with the characterized engine as a source and exhaust sound output as a result.

Linear Acoustic Exhaust System Simulation Using Source Data from Non Linear Simulation

The present invention relates to a converter device intended to be arranged in an exhaust system for a combustion engine. the converter device comprises an outer casing (1), a passage for leading exhaust gases through the converter device, a particle filter (7) arranged in said passage to remove particles from the exhaust gases, and a catalytic cleaner (10) arranged in said passage to effect catalytic cleaning of the exhaust gases. The particle filter (7) and the catalytic cleaner (10) are so positioned relative to one another that the exhaust gases flow through the particle filter (7) and the catalytic cleaner (10) in substantially parallel but opposite directions (8, 11) and that at least one plane (A) lperpendicular to said parallel directions (8, 11) extends through both the particle filter (7) and the catalytic cleaner (10).

Housing arranged in an exhaust gas system for a combustion engine

Study of a folded resonator including the effects of higher order modes

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