|Vol 36 No 1||
A Review of Airfoil Trailing Edge Noise and its Prediction
Transient vibration in a simple fluid carrying pipe system
Nicholas Steens and Jie Pan
Acoustical coupling between lip valves and vocal folds
Joe Wolfe and John Smith
Acoustics Australia Information
Vol. 36, No. 1 pp 7 - 13 (2008)
ABSTRACT: If technology such as aircraft, submarines and wind turbines are to further reduce their noise emissions, then a better understanding of airfoil trailing edge noise is required. This paper will discuss the physical causes of trailing edge noise and then review the methodologies used over the past couple of decades to model and to estimate trailing edge noise. A comprehensive reference list is given for readers wishing to learn more about this important area of aeroacoutsics. It is shown that one of the major restrictions to further development of prediction methods is a lack of suitable experimental data for validation purposes. Additionally, new turbulence models are needed to improve noise prediction, especially at high frequency.
Vol. 36, No. 1 pp 15 - 21 (2008)
ABSTRACT: This study aimed to investigate the behaviour of coupled transient acoustic and structural waves travelling within an L-shaped, statically pressurised, water filled pipe system consisting of two pipe straights separated by a pipe bend. Specifically, theoretical models were utilised to predict the time domain response of the system subject to a single, impulse-like excitation applied to a boundary modelled as an end cap. Two models of the bend were used: one utilised a simple discrete model and the other a more complicated continuous model. Moreover, an experimental rig was designed and built to test the theory. The designed ring frequency and ratio of bend radius to pipe radius were respectively 24 kHz and 4.4. The results show that for a broad impulse consisting of significant frequencies up to 1 kHz, the discrete bend model is superior to the continuous model due to computational efficiency.
Vol. 36, No. 1 pp 23 - 27 (2008)
ABSTRACT: In normal speech and singing, the standing waves produced in the upper vocal tract are thought to have relatively little effect on vocal fold vibration. We demonstrate the effect of acoustic waves on vocal fold motion. The waves, whose magnitudes are comparable with those produced by vocalisation, are produced by playing a pipe in the manner of a didjeridu. We monitor vocal fold and lip motion by measuring their electrical admittance through the skin, and compare them with the radiated sound. In the presence of deliberate vocalisation, interesting heterodyne effects are produced, which are visible in all three signals. When the folds are relaxed, or in the configuration used for whispering, standing waves produced by playing the pipe produce vibrations in the vocal folds whose magnitudes are comparable with those associated with active vocalisation.