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Content archived on 2024-04-30

Basic research on duct acoustics and radiation


Objectives and content
Objectives and content
Since fan noise will be a major contributor to the
exterior noise of Very High By-pass Ratio (VHBR) and
Ultra High By-pass Ratio (UHBR) turbofans, aerospace
industry is planning to introduce new nacelle noise
reduction technologies as adaptive and active liners
(actuators). Optimisation of these reduction means
requires a thorough understanding and accurate
description of the sound propagation in ducts.
Therefore, the main goal of DUCAT is to develop, extend
and validate computational methods for the propagation
and radiation of fan noise, including the effects of
acoustic liners. A number of relevant aspects of this
topic are not covered by the computation models existing
Duct acoustics design tools have to be reliable,
accurate, fast and versatile. According to aerospace
industrial needs, these models should ideally be able to
realistic nacelle geometries and non-uniform flow (in
intake and by-pass duct), - non-uniform acoustic liners
and duct wall mounted actuators,
radiation into the far field,
realistic frequencies and Sound Pressure Levels.
Within short terms, it is not expected that all aspects
can be addressed with a single model. Therefore in DUCAT
a small number of numerical models (Finite Element (FEM),
Boundary Element (BEM), coupled FEM/BEM, a non-linear
propagation model and a ray-acoustics model) will be
developed covering the whole frequency range of interest
for fan noise (kRmax = 100). Focal points for the
various models will be:
for the BEM-model: acoustic radiation and the inclusion
of non-uniform (potential) flow,
for the 3D-FEM-model: acoustic radiation in sheared
exhaust flow and 3-D nacelle geometry,
for the coupled 3-D FEM/BEM model: influence of
boundary layer flow on the effectiveness of liners,
for the non-linear model: effect of liners on
propagation just upstream of the fan,
for the ray-acoustics model: high dimensionless
frequencies (kR > 40).
These models are partially complementary and partially
overlapping, which offers the possibility to find the
best modelling for each aspect of duct acoustics.
The models will be validated by various experiments in
European anechoic wind tunnels. A main validation
experiment will be carried out using a model turbofan in
the German Dutch Wind Tunnel (DNvV). The experimental
data will constitute a database for the validation of the
codes developed in this project and for future
applications. Also data from the previously CECsponsored FANPAC-project will be used.
After validation, the range of applications of the models
and the restrictions for the use as industrial design
tools for nacelle acoustic optimisation will be
established. Furthermore, as a case study, a liner
design exercise on the nacelle of a generic VHBR turbofan
will be performed.
The final result of DUCAT will be an assessment of the
applicability of the various computational models for
duct acoustics problems and liner optimisation. With the
improved and validated models, the engine and aircraft
industry will have the possibility to develop adequate
design tools for both passive and active liner
optimisation. Further some spin-off to other industries
is foreseen, since fluid machines as pumps, fans and
internal combustion engines are major noise sources in
modern society.
The work in this project will clearly make progress
beyond the state of the art by developing and extending
computational models for duct acoustics and validating
those by a small number of precise experiments.

Call for proposal

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Nationaal Lucht- en Ruimtevaart Laboratorium
EU contribution
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8316 PR Marknesse

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Total cost
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Participants (11)