Active Control of Counter-Rotating Open Rotor Interior Noise in a Domier 728 Experimental Aircraft: Optimised Sensor Placement

For the next generation of aircraft, new engine and fuselage concepts are investigated because of the increasing demand for fuel efficiency and the CO2/NOx restrictions declared by the European Union. A lightweight design of civil aircraft combined with efficient engines like the counter-rotating open rotor (CROR) is a key technology to reach these ambitious goals. Especially in the lower frequency range, where the CROR blade-passing frequencies (BPF's) are dominating the acoustic response, the transmission loss of lightweight structures is typically poor. Active control techniques was tested on plates and beams to increase the system performance in terms of global vibration or sound power reduction. Yet to the authors' best knowledge, only very little work has been conducted to establish sensor or actuator position optimisation on a complex aircraft structure. The presented paper investigates the potential of a sensor position optimisation on a Dornier 728 experimental aircraft of the German Aerospace center (DLR). This experimental aircraft provides a real fuselage structure and the multi-sinusoidal CROR excitation is induced by a 112-channel loud speaker array. The system model of a fuselage segment is experimentally identified, a sensor optimisation is established and compared to empirically placed sensor configurations. The sensor optimisation includes the simulation of an multiple-input multiple output (MIMO) active feedforward vibration controller and the resulting sound radiating vibration patterns. It is shown in the experiments that the feedforward controller using optimised sensor locations reduces the radiated sound power by 7 dB, whereas the empirically placed sensors achieve only 4.5 dB. Furthermore, the potential of the proposed optimisation method regarding sound power reduction performance and the number of required sensors is shown for a real aircraft structure and a complex acoustic excitation.