Caracterização Experimental do Efeito de um Bocal com Chevron sobre o Campo Turbulento de um Jato Subsônico

Abstract

The turbulent jet issuing from engine exhaustion is one of the main sources of noise in an aircraft. This is a topic in the research field of aeroacoustics in which the sound generation mechanisms are not yet fully understood. However, some noise reduction devices have been developed and applied in aircrafts, such as tabs and chevrons. The present work addresses a comparison between the flow fields generated by nozzles with and without chevrons through hot-wire anemometry. The main goal was to understand the chevron effect on the flow field and the noise reduction mechanisms attributed to such nozzles. The results have shown an increase in axial turbulent intensity generated by the chevron in the initial region of the jet (x/D<2) and a decrease in turbulent intensity levels in the subsequent region. The chevron nozzle also increased the spreading of the jet and generated a thicker shear layer. The power spectral density showed the existence of coherent structures in the jet and the chevron was found to affect the energy peaks associated to these structures, specially at Strouhal number 0.3.