Project Title:

Aeroacoustic Diffraction and Dissipation by a Short Propeller Cowl in Subsonic Flight

02.10-1421
910079
Aeroacoustic Diffraction and Dissipation by a Short Propeller Cowl in Subsonic Flight
Cambridge Acoustical Associates, Inc.
80 Sherman Street
Cambridge
MA
02140
Rudolph
Martinez
617-491-1421
LeRC
NAS3-26598
025

02.10-1421
910079

Abstract:

Aeroacoustic Diffraction and Dissipation by a Short Propeller Cowl in Subsonic Flight
This project will investigate two concerns of the propfan noise research program:
 the beneficial effect of placing the new propulsion system within a short, diffractive
cowl and whether practical variations in the configuration of the acoustic liner
on such a cowl would significantly affect the character of the noise emerging from
its ends. A ducted-propeller theoretical model will be developed incorporating the
following physical features:  an idealized cowl of finite length, open-ended, unflanged,
and thin-walled; an axisymmetric liner that will cover parts of its interior surface
with variable material properties along the cowl's short axial extent; the effects
of a subsonic freestream (the flight speed) on the coupled phenomena of edge diffraction
and liner dissipation and on the propagation of the predicted radiated field; and
an insonifying aeroacoustic field due to a realistic distribution of modeled propeller
sound sources.
The design of acoustic liners specially tailored to short-ducted propellers will
address, respectively, the problems of cabin noise during flight (near-field radiation
patterns) and community environmental noise (far-field radiation patterns).
ducted propeller, linear optimization, diffracting cowl