Desenvolvimento e análise de um modelo para previsão do espectro do ruído de jatos, incluindo efeitos de temperatura

Abstract

A model is developed to obtain, from the spectrum of a cold jet at 90°, the corresponding spectrum for a heated or cold jet at any angle. The model uses the Lilley analogy – which considers a linearized wave equation for a parallel flow and regards the nonlinear terms as sources –, which includes explicitly flow-source interaction effects, and employs analytical solutions available in the literature for the case of uniform flow in the limits of high and low frequencies. The proposed solution is obtained from a general representation for the solution of the Lilley equation, which shows explicitly the velocity and temperature gradients, and the combined use of the asymptotic solutions. The model depends on the temperature, jet diameter, Mach number and frequency. It is shown that in addition to the terms corresponding to the cold jet, the hot jet involves new components with dipole and quadripolar efficiency, which are discussed. The comparison of the results predicted by the model with experimental data showed that the model performed reasonably well for angles outside the cone of silence. It also evidenced the importance of dipoles for small Mach numbers at low frequencies and the