Numerical and Experimental Analysis of Tuning Three Selected Types of Acoustic Helicoidal Resonators with 90-Degree Duct Elbow

This work presents the results of numerical and experimental analyses regarding the tuning of three selected acoustic helicoidal resonators using a 90-degree elbow in a cylindrical duct. The elbow is placed directly at the end of the resonators, which were additionally rotated about the duct axis at a specific angle (45° angle change in the numerical analysis and 90° angle change in the experiment). Three resonators with the same helicoid pitch-to-duct diameter ratio of s/d = 1.976 but with different numbers of turns n of 0.671, 0.695, and 1.0 were selected for analysis. They represent three different transmission loss (TL) characteristics in the frequency domain. In the considered system of helicoidal resonators and a 90-degree duct elbow, it was found that the selected resonators can be tuned by rotating them, effectively covering nearly the entire range of their characteristic sound attenuation resulting from acoustic resonance.