Noise From Turbojet Compressors

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Abstract
Summary: The noise radiated from the intakes of turbojet engines during landing is already causing a serious nuisance. This paper, which is largely based on the deliberations of an ad hoc working panel of academic experts formed by Rolls-Royce in 1961, describes the characteristics of the noise and discusses possible mechanisms of generation. The noise appears to be dipole in origin, and to come mainly from the first two compressor stages. It consists of a few discrete tone components, generated mainly by the interactions which occur when one row of aerofoils passes through the wakes of a preceding row; and broad band noise resulting from the turbulence in the wakes and the inherent instability of the boundary layer on the aerofoils.Some discrete tones may be eliminated over part of the running range by suitable choice of blade numbers and disposition. The broad band noise is unlikely to be reduced without major design modifications involving either a reduction of the air speed relative to the front stage blades, or removal of the boundary layer at their trailing edges.

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