Computer-aided liner optimization for broadband noise

In this article the attenuation of broadband noise in an acoustically-lined circular-section duct is investigated. The aim is to predict how an axially segmented liner influences the attenuation of broadband noise in an aero-engine intake. The sound field is modelled using a multi-modal representation, assuming an ensemble of uncorrelated modes over a wide range of frequencies. An optimization procedure based on a Response Surface Model is used to investigate the optimum uniform and axially-segmented acoustic liner that maximizes the attenuation of broadband noise. An approximate calculation of the Perceived Noise level (PNL) is used for the objective function. In this article the benefit of using an axially segmented liner instead of a uniform liner to attenuate broadband noise is demonstrated

Tradeoffs in jet inlet design: a historical perspective

The design of the inlet(s) is one of the most demanding tasks of the development process of any gas turbine-powered aircraft. This is mainly due to the multi-objective and multidisciplinary nature of the exercise. The solution is generally a compromise between a number of conflicting goals and these conflicts are the subject of the present paper. We look into how these design tradeoffs have been reflected in the actual inlet designs over the years and how the emphasis has shifted from one driver to another. We also review some of the relevant developments of the jet age in aerodynamics and design and manufacturing technology and we examine how they have influenced and informed inlet design decision

Response surface method optimization of uniform and axially segmented duct acoustic liners

An extensive duct acoustics propagation study is presented that has been conducted to assess the design of a liner for an aeroengine inlet duct. The aim is to predict how different liner configurations, at various flight conditions affect the attenuation of sound in an inlet. Two different noise source models are used: single mode and multimode. These represent the two principal fan noise sources: tonal and broadband noise. The two noise source models are then combined to predict the overall attenuation. An optimization procedure based on a response surface model is presented, to investigate a uniform and an axially segmented acoustic liner. The objective function used in the optimization is based on an approximate calculation of the perceived noise level. The aim is to utilize and axially segmented liner to increase, compared to a uniform liner, the overall sound attenuation that is predicted. The main feature that emerges is that it is possible to increase the attenuation with an axially segmented liner only when a limited number of propagating modes are present

Liner optimization using a hybrid finite element method

This paper makes use of a novel finite element method for aeroacoustics analysis to examine and optimise the design of liners for aeroengine inlets. The finite element approximation used is very efficient since it allows the treatment of non-axisymmetric nacelles by combining a standard biquadratic approximation in the axial and radial directions, with a spectral representation in the circumferential direction. Results from the code are used in a multi-fidelity optimization approach which is based on response surface and formal design of experiment methods. The design optimization also makes use of Grid computing technology to allow efficient use of computational resources and effective management of the analysis results. The use of these various techniques in combination allows for significant improvements to liner designs with realistic geometries at modest computational cost