Published online by Cambridge University Press: 04 July 2016
Noise reduction in the inlet of stationary gasturbines or aeroengines is usually achieved by passive absorbers (acoustic liners) the efficiency of which is limited due to the confined length. Higher sound level reductions can be obtained — in particular for the tonal components -by using additionally active noise control techniques (ANC): The rotorspeed-coherent tonal components of the primary sound field are superimposed with an anti-phase sound field which is produced by secondary acoustic sources.