In-Flight Acoustic Mode Measurements in the Turbofan Engine Inlet of Fokker 100Aircraft

摘要

A knowledge of the modal content prevailing in an engine inlet is of utmostimportance for designing the optimum acoustic treatment. This paper describes results of in-flight measurements of circumferential modes as carried out in the untreated and treated inlet of a Fokker 100 aircraft. In order to determine the modes, the inlet was instrumented with a large number of microphones and accelerometers. In addition static pressures in the vicinity of each microphone were measured. It is found that for the untreated inlet the modal energy at 1 BPF is concentrated in a few scattered modes, the modes being adjacent to the mode of the rotor with 22 blades. For treated inlet broadband modal spectra are found which cannot be directly related to the Tyler and Sofrin rule.