Development of Adaptive Acoustic Impedance Control Technologies of Acoustic Duct Liner

Hiroshi Kobayashi,Schunichi Ozaki,Makoto Yokochi

doi:10.1155/2011/473282

Abstract

This paper describes the development of adaptive acoustic impedance control (AAC) technologies to achieve a larger fan noise reduction, by adaptively adjusting reactance and resistance of the acoustic liner impedance. For the actual proof of the AAC technology III performance, the advanced fan noise absorption control duct liner II was made on trial basis, with the simple control system and the plain device. And, then, the duct liner II was examined for the AAC technology I, II, and III models, using the high speed fan test facility. The test results made clear that the duct liner II of the AAC technology III model could achieve the fan noise reduction higher than O.A. SPL 10 dB (A) at the maximum fan speed 6000 rpm, containing the reduction of fundamental BPF tone of 18 dB and 2nd BPF tone of 10 dB in response to the fan peed change from 3000 to 6000 rpm.

Highlights

Due to the strong demands by communities in the vicinity of airports, the new aircraft noise certification for the subsonic aircraft, ICAO Chapter 4, took effect in 2006 with the aim to reduce the aircraft noise.The ICAO Chapter 4 becomes substantially stringent for the development of the new subsonic and supersonic transports
For the actual proof of the acoustic impedance control (AAC) technology III performance, the advanced fan noise absorption control duct liner II was made on trial basis, with the simple control system and the plain device
3rd blade passing frequency (BPF) tone reduced by the adaptive duct liner II of the AAC technology I model are shown in Figure 10, against the mobile reflective plate position

Summary

Introduction

Due to the strong demands by communities in the vicinity of airports, the new aircraft noise certification for the subsonic aircraft, ICAO Chapter 4, took effect in 2006 with the aim to reduce the aircraft noise. The AAC technology I makes a large peak frequency shift and a big peak spectra increase of the acoustic absorption spectra of the duct liner for large fan noise reduction, by adjusting the reactance of acoustic impedance of the duct liner with the control of the reflective plate movement, in response to fan speed change. It controls the stepping motor equipments and determine both the position and the mode of the mobile reflective plate apparatus, and the porosity of the tunable perforated plate apparatus, so that the overall SPL measured by the sensing sensor of miniature pressure transducer can reach to the minimum of overall SPL

Test Facility and Test Procedure

Test Results and Discussion

Conclusion