Development of an innovative noise generation system for turboprop aircraft fuselage testing

This paper presents the development of a cabin noise testing equipment that will be
used to evaluate the interior noise of regional aircraft as well as to aid the development of noise
reduction techniques. The innovative noise generation system consists of three loudspeaker
arrays positioned around the fuselage circumference to synthesize a pressure field that is similar
to the pressure field seen by the fuselage during a flight. The acoustic pressure field generated
by the loudspeakers is measured by a number of microphones scattered on the fuselage surface.
These microphone signals are then fed back to the controller with the purpose of minimising the
error between the target pressure field and the measured one by means of an iterative learning
approach. The number and location of the microphones used in the control loop are selected
through a pre-test optimisation analysis, which aims to reduce the time and cost of the set-up. A
small-scale electroacoustic demonstrator has been built to develop the feedback control
approach. A frequency domain multi-input multi-output feedback controller is used to replicate
the random pressure field generated by the turbulent boundary layer excitation. The multiharmonics
of the propeller induced excitation are then added to the time histories of the
broadband noise using a time waveform replication technique. Different arrangements of the
driving signal distribution are investigated, and the results are then presented in terms of accuracy
of the pressure field reproduction.