Amplification of Jet Noise by a Higher-Mode Acoustical Excitation

As shown in previous experiments, the broadband sound radiation of a turbulent jet can be amplified by a pure-tone sound excitation. This interaction takes place at perturbation levels lower than those found in aircraft engines. The previous experiments, however, have been carried out only with sound excitation of plane sound waves coming from inside the nozzle. In contrast to that, the present investigation shows that broadband jet noise amplification can be produced even by an acoustical excitation at higher modes. At exciting frequencies below the cut-on frequency of the nozzle exit cross section, the exciting tone is masked by the amplified jet noise in the radiated far field.