Experimental study of truncated-cylinder struts for noise reduction of large-scale landing gears

Abstract

Landing gears are an important noise source of aircraft during approach and landing, which makes the research on their aerodynamic noise reduction a topical problem. This paper experimentally studies the method of noise reduction developed by the authors, which consists in using truncated-cylinder elements for landing gears instead of circular-cylinder parts (e.g. struts, links, actuators, etc). The method stems from a theoretical interpretation of the experimental results obtained for bluff body noise measured with the help of azimuthal decomposition technique, and its efficiency has been many times demonstrated in tests with small-scale models. The present work continues these studies in application to large-scale generic landing gears and natural Reynolds numbers (up to Re = 2.4·106); it reports the results of experimental tests performed in a large anechoic wind tunnel. The large-scale experiments have shown that the truncated-cylinder strut could lead to broadband noise reduction of landing gear noise by up to 2 dB, which thus validates the noise reduction method demonstrated earlier for the small scales only. Beamforming source localization shows that the noise source in the frequency region where noise reduction is observed is associated with the strut. These results obtained for the large-scale models at natural Reynolds numbers allow the noise reduction method of cross-section shape modification to be recommended for implementation in low-noise landing gear design for struts and other cylinder elements.