![]() Previous researches mainly focus on the theories of BEM method, and some basic verification cases of acoustic scattering effects with simple solid boundaries such as spheres and plains. Curle studied the influence of solid boundaries upon aerodynamic sound and the acoustic scattering effects of the solid boundaries. Seongkyu Lee, Kenneth Brentner and Philip Morris studied the scattering effects in the time domain using an equivalent source method, with a sphere solid scattering boundary and a point sound source. ![]() Roger Michel and Kucukcoskun Korcan studied the scattering effects of the solid strut member of a rotor and put forward some relevant theories. Some basic researches based on boundary element method (BEM) have been brought out for calculations of acoustic scattering effects. The helicopter fuselage can be regarded as a solid boundary and thus BEM method can be a proper method adapted to the calculation of its acoustic scattering effects. Compared with ESM that should disperse the whole domain, BEM just requires the dispersal of the boundary, transferring three dimensional problems into two-dimensional problems so that the complexity and workload can be reduced. Common methods include equivalent source method (ESM) and boundary element method (BEM). Therefore a method is required for the calculation of the acoustic scattering effects of the helicopter fuselage. However, not all of the sound waves travel directly in straight lines to infinity, for the existence of helicopter fuselage that brings acoustic scattering effects for its reflection of sound waves. ![]() have deduced convective Kirchhoff equation for the calculation of sound field. Taking account of the influence of medium movement (inflow), Ghorbaniasl and Lacor have developed a direct calculation method of the sound field of rotating sound sources with inflow, based on convective FW–H equation, and also developed several time domain formulations for the solution of the convective FW–H equation. The Ffowcs Williams and Hawkings (FW–H) equation is a standard approach to the solutions of this sort of problems. It is commonly acknowledged that the rotor blades are regarded as the main acoustic noise source of a helicopter, whose acoustic noise prediction problem can be regarded as the calculation of the sound field of rotating sound sources. Predicting the acoustic noise is one of the important parts of aircraft acoustic stealth technology, helping to ascertain the sound pressure level of acoustic noise and find out the main affection factors. Therefore it is essential that a proper stealth design is adopted for a new helicopter, aiming at suppressing its acoustic noise and strengthening its acoustic stealth ability. The most important characteristic signal of helicopters is acknowledged to be acoustic noise, which can be a severe problem of the acoustic stealth of helicopters. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( ), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Besides, the research in this paper leads to the discovery of the influence factors of the acoustic scattering effects and helps the proper selection of the fuselage in a helicopter stealth design. ![]() The presented FBM is efficient to analyze the acoustic scattering effects of the helicopter fuselage and predict the acoustic noise field, taking both the rotor and the fuselage into account. In addition, the acoustic scattering effects of the same type of fuselage but with different length, width and height ratios are also compared for discovering the influences of the fuselage size. According to the discovery that helicopter fuselages with sharp edges can bring more significant acoustic scattering effects, a research on the influence of radius of curvature (RC), which reflects the sharpness of fuselage sharp edges, is also carried out. In this paper, different fuselage models are adopted for the comparisons of the acoustic noise scattered by different types of fuselages. For the accuracy of acoustic noise prediction and the research on the scattering affections of the helicopter fuselage, an FWH–BEM Method (FBM) based on convective FW–H equation and boundary element method (BEM) is presented for the prediction of the noise scattering effects of helicopter fuselage and the approach to the calculation of a helicopter’s acoustic noise field. * Corresponding author: main acoustic noise source of helicopters is supposed to be the rotor blades, but the scattering effect of the helicopter fuselage sometimes cannot be ignored. Beihang University, 100191 Beijing, China ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |