ARTICLE | doi:10.20944/preprints202009.0117.v1
Subject: Engineering, Marine Engineering Keywords: underwater radiated noise; propeller; Ffowcs William-Haukings; permeable FW-H; BEM
Online: 5 September 2020 (04:59:07 CEST)
The sound field properties for non-cavitating marine propellers are studied using FW-H (Ffowcs William-Hawkings) acoustic analogy and BEM (Boundary Element Method) approach. For the first time, the FW-H formula to calculate acoustic pressure generated by the propeller wake sheet is proposed. The corresponding sound signal can be dominant up to several kilometres. Secondly, non-physical fictitious volume flux is observed when the permeable FW-H approach is used together with BEM. The reason is explained and a virtual source correction method is proposed to solve this problem. Furthermore, analytical analyse show that the second thickness term and the first two loading terms in Farassat 1A formula are important, and the others are negligible. The numerical studies show that the permeable FW-H approach produces underestimation when compared to the direct FW-H method, and the underestimation is severer for larger permeable surface and higher frequency. It is also found that the first loading term in Farassat 1A formula is the dominant source term in the direct FW-H method, while the first thickness term is dominant when the permeable FW-H approach is used.
ARTICLE | doi:10.20944/preprints201802.0032.v1
Subject: Physical Sciences, Acoustics Keywords: inverse acoustic problem; helicopter rotor; Ffowcs Williams and Hawkings equation; aerodynamic constraint; Thikhonov method
Online: 5 February 2018 (11:34:30 CET)
An inverse aeroacoustic problem for a helicopter rotor combined with aerodynamic constraint is proposed based on Ffowcs Williams and Hawkings equation in subsonic. The rotor noise includes thickness noise and loading noise when quadrupole noise is neglected. Thickness noise is related to geometry and motion conditions. Loading noise is related to the pressure on the wall. Therefore, the equation between pressure on the wall and far-field noise can be established, thus the pressure on the wall can be obtained by solving this equation. Since this equation is an ill-posed, the singular value decomposition combined with the regulation method is applied and the aerodynamic constraint is taken into account. The direct noise prediction is verify firstly and then the inverse problem is solved. The reconstruction pressure is compared to the input data. The result is in good agreement with the input value. At the same time, the influence of interference noise is also considered. Under low signal-to-noise ratio, the reconstruction result is also reasonable.