W. Eversman

A finite element model is created for the generation, propagation, and radiation of steady, rotor alone noise and rotor and exit guide vane interaction noise of a ducted fan. In the case of rotor alone noise the acoustic source is represented by a rotating lifting line of thrust and torque dipoles distributed radially on the blade. For a specified number of blades, angular mode harmonic, and rotor angular velocity, the acoustic field is described in a cylindrical coordinate system reduced to only the axial and radial directions. The blade loading is imposed on a radial line at the axial location of the fan. The blade loading is assumed to vary linearly from the hub to the tip. The blade tip loading is determined by a specified thrust requirement and the inflow velocity. In the case of interaction noise the acoustic source is a stationary lifting line of torque and thrust dipoles which represents the fluctuating lift on the exit guide vane created by the velocity deficit associated with wakes in the steady velocity field behind the rotor. The fan and exit guide vanes are imbedded in a duct which can be contoured to represent a realistic installation. In ·the configurations considered in the present study, emphasis is on ducted fans or ducted propellers for which the by-pass ratio is very large. In this case the usual assumption is made that the fan, or propeller, is operating in a mean flow environment which is uniform and the same as the forward flight velocity. The flow acceleration in the inlet, acceleration in the fan duct, and jet free shear layer are not accounted for in the present model. The model accounts for the noise generation process, the propagation through the inlet and fan duct, and the radiation to the near and far field. The major issue addressed in the computational examples is the relationship between the far field radiated Sound Pressure Level (SPL) and directivity and fan tip speed.

DGLR/AIAA 14th Aeroacoustics Conference, 1992

Conference Paper

englisch

21,0 x 29,7 cm, 10 Seiten

DGLR-Bericht, 1992, 1992-03, DGLR/AIAA 14th Aeroacoustics Conference - Proceedings; S.836-845; 1992; Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn

NA

aeroacoustics

Bibliothek

1992