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An experimental and analytical study of the tonal trailing-edge noise of a symmetric NACA-0012 aerofoil and of a cambered SD7003 aerofoil has been achieved. It provides a complete experimental database for both aerofoils and improves the understanding of the underlying mechanisms. The analysis stresses the high sensitivity of the tonal noise phenomenon to the flow velocity and the angle of attack. Several regimes of the noise emission are observed depending on the aforementioned parameters. The contributions of the pressure and the suction sides are found to vary with the flow parameters too. A special attention has been paid to the role of the separation bubble in the tonal noise generation. Hot-wire measurements and flow visualization prove that the separation bubble is a necessary condition for the tonal noise production. Moreover, the bubble must be located close enough to the trailing edge. Several tests with small-scale upstream turbulence confirm the existence of the feedback loop. Analytical predictions with a classical trailing-edge noise model show a good agreement with the experimental data; they confirm the cause-to-effect relationship between the wall-pressure fluctuations and the radiated sound. Finally, previously reported works on fans and propellers are shortly re-addressed to show that the tonal noise associated with laminar-boundary-layer instabilities can take place in rotating blade technology.

Abstract.A survey of 158 sources (bipolar outflows and methanol masers) was carried out in the CS(2 − 1) and C 34 S(2 − 1) lines to measure and compare densities in a large number of bipolar outflows and in Class I and Class II methanol masers, both associated with and unrelated to bipolar outflows. The statistical characteristics of the regions, forming Class I methanol masers differ from those both in the centres of bipolar outflows and in the regions forming Class II methanol masers. It is possible that physical conditions in bipolar outflows are closer to physical conditions of Class II methanol masers.