Using the Correlation Model of Random Quadrupoles of Sources to Calculate the Efficiency of Turbulent Jet Noise Screenin
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SPHERIC AND AEROACOUSTICS
Using the Correlation Model of Random Quadrupoles of Sources to Calculate the Efficiency of Turbulent Jet Noise Screening with Geometric Diffraction Theory S. L. Denisova, *, V. F. Kopieva, **, N. N. Ostrikova, ***, G. A. Faranosova, ****, and S. A. Chernysheva, ***** a
Central Aerohydrodynamic Institute (TsAGI), Moscow, 105005 Russia *e-mail: [email protected] **e-mail: [email protected] ***e-mail: [email protected] ****e-mail: [email protected] *****e-mail: [email protected] Received March 23, 2020; revised April 17, 2020; accepted April 28, 2020
Abstract—The paper presents the results of a computational–experimental study of jet noise reduction using the screening effect. According to correlation theory, the noise sources of a single circular jet are represented by a set of uncorrelated quadrupoles. Using the basic relations of geometric diffraction theory (GDT), expressions are obtained for the sound field emitted by a point quadrupole source located near an acoustically rigid infinite half-plane. Using the expressions obtained in the framework of the GDT, the correlation model of the jet noise sources was adapted to the calculation of the sound field in the presence of a flat rectangular screen. A comparison of the calculated and experimentally measured spectra of sound pressure levels, performed at a given jet velocity and various screen positions, showed good qualitative, and for certain observation angles, quantitative agreement. Keywords: turbulent jet noise, jet noise correlation theory, sound wave diffraction, geometric diffraction theory (GDT), screening efficiency DOI: 10.1134/S1063771020050024
INTRODUCTION Turbulent jet noise, as is well known, is an important component of the modern aircraft community noise. For over 60 years, it has been the focus of experimental, theoretical, and computational research. One way to reduce the jet community noise is to screen it with various airframe elements. At the same time, despite a significant history reaching back to the 1970s, the theoretical description of jet noise screening is far from complete. The first computational and experimental jet noise screening studies were performed in [1–3], which also proposed simplified computational models for describing jet noise itself. A jet as a sound source was represented as a set of monopoles distributed along the axis or as a point source at the nozzle exit with a directivity pattern corresponding to jet emission in the far field. Diffraction of sound emitted by such sources was calculated using the Maekawa method [4] or the MacDonald solution for a halfplane [5]. The results of these studies, performed for single turbojet and low-bypass engines, showed an
extremely high potential for reducing jet noise using the screening effect, which became the impetus for developing novel assembly schematics for new-generation aircraft, in which the screening effect could be fully realized. However, active improvement in turbojet engine design (the transition to large
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