Abstract
Preparing and pre-testing experimental setups for flight tests is a lengthy but necessary task. One part of this preparation is comparing newly available measurement technology with proven setups. In our case, we wanted to compare acoustic Micro-Electro-Mechanical Systems (MEMS) to large and proven surface-mounted condenser microphones. The task started with the comparison of spectra in low-speed wind tunnel environments. After successful completion, the challenge was increased to similar comparisons in a transonic wind tunnel. The final goal of performing in-flight measurements on the outside fuselage of a twin-engine turboprop aircraft was eventually achieved using a slim array of 45 MEMS microphones with additional large microphones installed on the same carrier to drawn on for comparison. Finally, the array arrangement of MEMS microphones allowed for a complex study of fuselage surface pressure fluctuations in the wavenumber domain. The study indicates that MEMS microphones are an inexpensive alternative to conventional microphones with increased potential for spatially high-resolved measurements even at challenging experimental conditions during flight tests.
Highlights
The characteristics of pressure fluctuations on the airplane fuselage govern the vibroacoustic excitation of surface panels exposed to the boundary layer flow
The paper describes the process of preparing Mechanical Systems (MEMS) microphones within a flexible circuit board array for the measurement of unsteady pressure fluctuations on an airplane fuselage during flight tests
The MEMS sensors have a small sensitive surface area which allowed them to capture the presence of high-energy small-scale structures within the turbulent boundary layer when pre-testing them in a low-speed wind tunnel environment
Summary
The characteristics of pressure fluctuations on the airplane fuselage govern the vibroacoustic excitation of surface panels exposed to the boundary layer flow. These pressure fluctuations are caused either by the Turbulent Boundary Layer (TBL) itself or acoustic fluctuations induced by-for instance-the engine or by airframe noise. Flight tests are an appropriate method to obtain knowledge about the characteristics of these pressure fluctuations under realistic conditions. Sensors suitable for this task require a high overload point to resolve the highamplitude pressure peaks within the turbulent boundary layer. Small sensors suitable for capturing both acoustic and hydrodynamic pressure fluctuations are to our knowledge not very common
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