Preliminary results of a MIMO Harmonic Controller to perform active sound power attenuation with a RHAPSODI

A Harmonic Acoustic Pneumatic Source (HAPS) is an acoustic device developed to perform active harmonic sound control in turbofans. In order to develop a demonstrator, a ring of multiple HAPS (RHAPSODI) is assembled around a cylindrical duct and a dedicated MIMO harmonic controller was developed to perform active sound power attenuation. The control objective is to develop a MIMO feedback controller adapted to multiple HAPS and using in-duct microphones close to them. Three points are addressed : the control of HAPS as a mechanical modulator, the in-duct error microphones located in the near field of HAPS, and the tuning of the controller. The presented method is based on a dedicated MIMO feedback controller of complex envelops with compensation of near field. The compensation matrix of the near field is tuned during a learning phase based on the measurement of a set of optimal commands experimentally obtained with a dedicated controller using the out-duct microphones. When the matrix of compensation is estimated, the MIMO controller using induct microphones can be used. Preliminary experimental results show that a RHAPSODI of 5 HAPS can attenuate the first harmonic of a radiated tonal sound power by more than 20dB.