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The excitation of trapped diametral acoustic modes within a rectangular cavity attached to a cylindrical duct is investigated numerically and experimentally. Because the excited acoustic modes are ...

Most aeroacoustic noise-prediction methods rely on an acoustic analogy featuring a propagation equation associated with source terms. These models were mainly applied to computation of acoustic far fields radiated by simple free flows like jets. The assumption is made in many formulations that the radiated acoustic field is not perturbed by the shear flow giving rise to the noise sources. These acoustic analogies thus do not provide a full description of acoustic/flow interactions. The Lilley equation was introduced to account, to a certain extent, for mean shear effects on propagation. More recently, this problem has been treated by making use of the linearized Euler equations, which are more flexible and more adequate for numerical simulations. As several types of modes are supported by the Euler equations, problems linked to their coupling have to be considered. It is then necessary to investigate acoustic field computations in complex flows. Our aim in the present article is to validate the wave operator associated with linearized Euler equations. Numerical tests deal with propagation in two-dimensional sheared ducted flows. Results are compared with other solutions deduced from analytical developments and direct numerical simulations. This study shows that the linearized Euler operator may be used to account for mean effects on wave propagation in the presence of sheared ducted flows. Processes that are specifically considered are 1) convection effects on axial disturbances, 2) refraction effects on oblique wave generation, and 3) source radiation effects on propagation in sheared flows.

Subsonicandsupersonicjetnoiseisdeterminednumerically from statisticalsourcemodels.Thegoalistodevelop prediction methods for high-speed jet noise for application to aeronautical and space transportation systems. In this framework, a combination of a k-≤ turbulence closure with an acoustic analogy provides an interesting way to compute such radiated acoustic e elds. Three acoustic analogies are investigated. First, the classical Lighthill theory in combination with Ribner' s results is applied to calculate jet mixing noise. The second method relies on the Goldstein -Howes convected wave equation, which is used to improve the predicted supersonic jet mixing noise in the upstream direction. It is necessary to properly account for acoustic wave convection, and then, one e nds that the Doppler factor features an exponent of i 3 in the associated power law. A model based on the Ffowcs Williams-MaidanikanalysisthenisdevelopedtoestimatetheMach-wavenoisecomponentthatdominatesforward arc radiation when theconvection Mach number is supersonic. Comparisons between aerodynamicand calculated acoustic results on the one hand, and available measurements on the other hand, are carried out. It is shown that the last two models yield improved supersonic jet mixing noise predictions.