An Investigation of the Inlet and Exhaust Noise Sources of Turbofan Using Linear Microphone Array

Abstract

This paper presents noise source location results for a turbofan engine with the bypass ratio of 2.4 obtained from engine static test, in which the engine was installed on aircraft. Source location data from this test was used to develop engine inlet sound absorbing liner and to design the aircraft fuselage sound insulation device. A linear array of 32 microphones was used in this program to determine the jet noise source distribution for the exhaust and the fan noise from inlet. Aeroacoustic beamforming with the delay and sum scheme in time domain was modified using the DAMAS deconvolution algorithm. Data were obtained for the engine power setting which is from 60% to 90% of the design power. It was shown that the noise source was one centralized source from engine inlet, and the location of this centralized source was almost immobile. The multiple sources were also detected in exhaust noise, and the location of distributed source was moving backward with the increase of engine power(that is with the increase of jet velocity). The haymow spectrum was observed for the exhaust noise, and obvious tone noise was observed in the spectrum of inlet noise.

An industrial onsite methodology for combined acoustic-aerodynamic diagnostics of axial fans, involving the phased array microphone technique

“…However, the literature is very limited in this regard. In particular case studies, [6][7][8] although the duration of averaging (recording) is reported, 18 these cases are restricted to the use of conventional algorithms capable for detecting standing sources. No direct recommendations were found in the literature for the appropriateness of averaging of PAM records in application of the ROSI algorithm.…”

“…The subjects of experimentation are mostly not industrial ventilating fans but aero-engine fans. 3,4,[6][7][8] The ROSI algorithm is still rarely applied. 1,4 In the cases when multiple microphones are used in diagnostics of industrial ventilating fans, the supplement of acoustics measurements by aerodynamic experiments is either lacking 5 or is usually confined to global data.…”