DAGA 2010 - Deutsche Gesellschaft für Akustik eV

292 DAGA 2010 Programm
to previous related findings and the relative influence of perceptual and
acoustic factors on musical timbre identification is discussed.
Do. 8:30 Grashof C 116 Aeroakustik Versuch/Simulation II
Glottal Jet Instabilities: Mechanisms, Control and Effect on Primary
Acoustics in Voice Generation
C. Brücker, M. Triep, W. Mattheus und R. Schwarze
Institut für Mechanik und Fluiddynamik, TU Bergakademie Freiberg
The opening and closing of the glottal orifice is responsible for a complex
flow field in the vocal tract as well as for the primary acoustic sources in
voice generation. This paper presents the flow results of an experimental
and numerical study on the jet formation, evolution and disintegration in
a glottal cam model. The modelled glottal orifices take into account the
three-dimensional (3-D) contouring of natural glottal gaps. Instabilities of
the jet head and the jet edge are analyzed with regard to the involved
mechanisms. The incidence of coherent structures in the jet edge and
in part their coalescence is detected. Observed phenomena such as a
length-wise vena contracta and axis-switching are supposed to play an
important role in the control of the glottal jet. A redistribution of the vortex
structures has shown to lead to a different character of the flow-induced
primary acoustic sources in the region downstream the glottis. This trend
is assumed to be enhanced when the glottal jet also interacts with the
vocal tract walls or other supraglottal structures.
Do. 8:55 Grashof C 116 Aeroakustik Versuch/Simulation II
Airframe Noise Reduction via Near-Wall Turbulence Control
S.R. Koh, W. Schröder und M. Meinke
Institute of Aerodynamics, RWTH Aachen
Turbulence control has been one of the major research issues to improve
the aerodynamic performance at high Reynolds number. In recent years
the progress in understanding of turbulent flow phenomena focuses on
energy saving technology. Furthermore, noise reduction is an important
issue to develop silent engines in various applications. The main objective
of the present study is to improve an active noise control technique
by manipulating turbulent shear layers. To achieve the noise reduction
multi-species gas mixtures are injected from a streamwise slot on
the wall surface. The control of the near-wall coherent structures changes
the velocity gradient in the shear layer and weakens turbulent wallpressure
fluctuations which have been directly recognized as the major
source of airframe noise. To reduce the computational costs the present
investigation focuses on the nozzle tip of a jet engine. That is, the simplified
physical problem represents a fluid controlled wall-bounded shear
layer passing over a trailing edge. The computational method adopts the
large-eddy simulation (LES) of non-reactive multi-species gas mixture
and solves the acoustic perturbation equations (APE) for the acoustic
field.