Sensitivity issues in active control of circular duct modes using axially-spaced actuator arrays

摘要

Active control of noise in two and three-dimensional environments poses significant challenges compared to suppression of plane-wave sound in a small duct. These challenges are exacerbated in aircraft engine nacelles, where space and weight are at a premium and where flow disturbances can result In a pronounced increase in noise. Although significant progress has been made in active suppression 4f noise in these difficult environments, the performance of physically implemented control systems has as yet fallen short of "on paper" expectations. Some of these shortfalls can be attributed to high sensitivity to component variations. Others are the result of inadequately discriminating sensor and actuator arrays. This paper compares predicted and observed performance of active control system installed in cylindrical ducts and used to control multiple circumferential and radial mode sound fields. Actuator array radiation efficiency suffers when targeting multiple modes. This amplifies the influence of cut-off modes and modal distortion caused by actuator nonuniformity on the effectiveness of active noise suppression.