Experimental aeroacoustic studies of selected three types of helicoidal resonators

The paper presents experimental studies of selected three types of helicoidal resonators carried out on an aeroacoustic laboratory stand with the use of pink noise and a duct terminated with a reverberation chamber. The same ratio s/d = 1.976 is considered for three numbers of helicoidal turns n = 0.671, n = 0.695 and n = 1.0. The results of the acoustic attenuation performance depending on the air flow velocity were compared in relation to the numerical tests carried out, which resulted in a decrease in resonance frequencies with an increase in the air flow velocity. The measurements were carried out with a high resolution of the FFT spectrum in order to illustrate the changes in the acoustic attenuation performance as accurately as possible. One-third octave bands of flow noise studies were also carried out.