Computation of far-field tone noise levels for radial and swept and leaned stators

Abstract

In this paper, the benefits of stator vane sweep and lean for reducing sideline tone noise produced by rotor-stator interaction are examined. The sideline sound pressure levels are computed using a finite element model of noise radiation and compared with measured levels. The in-duct levels, needed as input for the radiation study, are computed horn a model for predicting rotor-stator interaction tone noise. Four stator configurations are considered: a conventional radial stator at two axial positions (nominal and aft), a swept-only stator, and a swept and leaned stator. periodic impingement of rotor wakes on the stator vanes. Over the past three decades, several theoretical and experimental studies have indicated the potential noise benefits of sweep and lean [Refs. I-S]. Recently, NASA and the Allison Engine Company, under the sponsorship of the AST program, carried out a design-build-verification study of the vane sweep and lean concept. A detailed assessment of the acoustic performance of the swept and leaned stator is carried out by comparing its predicted and measured noise reductions relative to the other three stators. Overall, these comparisons show that the predicted benefits of the swept and leaned stator are in good agreement, qualitative as well as quantitative, with the measured noise reductions for the fan speeds that are relevant to the standard noise certification process. The results also demonstrate the usefulness of the theoretical tools employed in the study. Sweep is defined as the axial displacement of the vane leading edge from its baseline position. Similarly, lean is defmed as the circumferential displacement of the vane leading edge from its baseline position. Sweep is taken as positive when the vane tip is downstream of its root as shown in Figure (1 a), and lean is taken as positive when the vane tip is leaned opposite to the direction of fan rotation as shown in Figure (1 b).