Abstract:
A closed loop control system comprising of the feedback controller and the multiple pressure sensors is developed and evaluated in the wind tunnel test, where the active flap is used as a test bed of the active technique for noise reduction. The feedback controller utilizes a global model with on-line identification for the BVI noise reduction. By taking into consideration for the application to real helicopters, the BVI index generated from the pressure fluctuation on the blade is used for a control object. The control object by multiple pressure sensors which can more sufficiently represent the BVI phenomenon on the blade than by a single sensor is proposed and its capability is studied experimentally using a 1-bladed rotor system equipped with the active flap and the pressure transducers. The strong correlation between the sound pressure level measured near the blade and this BVI index generated from the surface pressure fluctuation by multiple pressure sensors is observed. Also, from the closed loop test results, a good convergence for the active flap phase of the minimum pressure fluctuation and the minimum SPL is obtained. It is concluded that the validation of the proposed control law is demonstrated and the control object utilizing the multiple pressure sensors is promising.