A.R. George, C.D. Coffen, T.D. Ringler

Noise is one of the most serious limitations on the possible introduction of tilt rotor aircraft to commercial markets. The two most serious tilt rotor external noise problems, hover noise and blade-vortex interaction noise, are studied in this paper. Hover flow measurements were perfonned on a 1/12 scale model of the XV-15 tilt rotor aircraft. The results of the flow visualization and inflow velocity measurements document a complex, recirculating highly unsteady and turbulent flow due to the rotor-wing-body interactions characteristic of tilt rotors. It is found that the wing under the rotor obstructs the inflow causing a deficit in the inflow velocities over the inboard region of the rotor. The bubulence intensities in the inflow are very high in the recirculating fountain reingestion mne. Discrete frequency harmonic thickness and loading noise mechanisms in hover were studied by first modelling tilt rotor hover aerodynamics and then applying various noise prediction methods using the WOPWOP code. The analysis indicate that the partial ground plane created by the wing below the rotor results in a primary sound souree for hover. Broadband noise mechanisms were also studied using a modification of Amiets method. The results indicate that the high turbulence level in the reingestion mne is the dominant source of broadband noise for a hovering tilt rotor. In forward or descending flight the most serious tilt rotor noise is due to interactions of the rotor blades with their or other rotor blades wake vortices. The directionality and strength of the important blade-vortex interactions (BVI) are explained through a radiation cone concept which is explained in this paper. The radiation cone effect is a highly directional mechanism which results when a lift distribution or perturbation moves supersonically with respect to the fluid. After a physical explanation of BVI mechanisms, the radiation cone concept is then applied to specific rotorcraft cases where it helps to explain zones of intense sound pressure level found in experimental results for the XV-15 tilt rotor.

DGLR/AIAA 14th Aeroacoustics Conference, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 22 Seiten

DGLR-Bericht, 1992, 1992-03, DGLR/AIAA 14th Aeroacoustics Conference - Proceedings; S.510-531; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

rotor blades, aeroacoustics, tilt rotor aircraft

Bibliothek

1992