An investigation into feasibility of impingement heat transfer and acoustic abatement of meso scale synthetic jets

Acoustic filters have a wide range of applications, yet customizing them with desired properties is difficult. Motivated by recent progress in additive manufacturing that allows for fast prototyping of complex shapes, we present a computational approach that automates the design of acoustic filters with complex geometries. In our approach, we construct an acoustic filter comprised of a set of parameterized shape primitives, whose transmission matrices can be precomputed. Using an efficient method of simulating the transmission matrix of an assembly built from these underlying primitives, our method is able to optimize both the arrangement and the parameters of the acoustic shape primitives in order to satisfy target acoustic properties of the filter. We validate our results against industrial laboratory measurements and high-quality off-line simulations. We demonstrate that our method enables a wide range of applications including muffler design, musical wind instrument prototyping, and encoding imperceptible acoustic information into everyday objects.

Acoustic voxels: computational optimization of modular acoustic filters

A procedure for measuring the acoustic scattering matrix coefficients of a duct discontinuity for higher order acoustic duct mode propagation conditions is described and tested. The technique requires measurement of pressure waves per mode coming in and out of the discontinuity. Assuming N cut-on modes, the (2N)2 scattering matrix coefficients are determined after repeating the experiment for N linearly independent pressure distributions for at least two load configurations. Experiments were conducted for a straight duct and a reactive chamber. A good agreement was found between experiment and theory except near cut-off frequencies. The overdetermination method based on four loads was shown to improve the results. An analytical simulation of the experiment was developed to compute the influence on the [S] calculation of an error in temperature and total modal pressure assumed to be representative of a real measurement situation. This simulation with a discussion explains the discrepancies between experiment and theory. The test with the chamber shows that the load method fails as expected in determining the coefficients associated to the wave coming in the discontinuity from the open end side because of the property of the middle duct to filter modes making the results very sensitive to uncertainties.

Multiload procedure to measure the acoustic scattering matrix of a duct discontinuity for higher order mode propagation conditions

Acoustic properties of biodegradable composite micro-perforated panel (BC-MPP) made from kenaf fibre and polylactic acid (PLA)

Study of multi-chamber micro-perforated muffler with adjustable transmission loss

The most common approach for measuring the transmission loss of a muffler is to determine the incident power by decomposition theory and the transmitted power by the plane wave approximation assuming an anechoic termination. Unfortunately, it is difficult to construct a fully anechoic termination. Thus, two alternative measurement approaches are considered, which do not require an anechoic termination: the two load method and the two-source method. Both methods are demonstrated on two muffler types: (1) a simple expansion chamber and (2) a double expansion chamber with an internal connecting tube. For both cases, the measured transmission losses were compared to those obtained from the boundary element method. The measured transmission losses compared well for both cases demonstrating that transmission losses can be determined reliably without an anechoic termination. It should be noted that the two-load method is the easier to employ for measuring transmission loss. However, the two-source method can be used to measure both transmission loss and the four-pole parameters of a muffler.

A Review of Current Techniques for Measuring Muffler Transmission Loss

Prediction of Sound-Absorbing Performance of Micro-Perforated Panels Using the Transfer Matrix Method

The two-source method was used to measure the bulk properties (complex characteristic impedance and complex wavenumber) of sound -absorbing materials, and results were compared to those obtained with the more commonly used two-cavity method. The results indicated that the two-source method is superior to the two-cavity method for materials having low absorption. Several applications using bulk properties are then presented. These include: (1) predicting the absorptive properties of an arbitrary thickness absorbing material or (2) layered material and (3) using bulk properties for a multi -domain boundary element analysis.

Z. Tao

Papers

A Review of Current Techniques for Measuring Muffler Transmission Loss

Prediction of Sound-Absorbing Performance of Micro-Perforated Panels Using the Transfer Matrix Method

Measuring Bulk Properties of Sound-Absorbing Materials using the Two-Source Method

Using Boundary Element Analysis to Analyze Multi-Component Exhaust Systems

Identification of AeroAcoustic Noise Sources Using Inverse Boundary Element Method