Experimental Investigation of Jet Flow Fields with Chevron Nozzles

Abstract

With the rapid development of the aircraft industry, more regulations on aircraft noise are established. The turbulent jet is one of the major sources of noise in the aircraft, extensive researches on noise reduction has been investigated, especially for chevron. In this project, the near-nozzle flow fields of three chevron nozzles and one circular nozzle from a subsonic jet are investigated experimentally. This paper presents the results the comparison between four nozzles (CN0, CN1, CN2 and CN3) in terms of radial mean velocity, turbulent intensity and the selected nozzles are compared to baseline and each other with respect to turbulent kinetic energy spectra. CN0 is the baseline circular nozzles, CN1 is the standard chevrons nozzle, CN2 is a chevron with alternating angles and CN3 is chevron with more number of chevrons. Fluctuated velocity profiles were measured at x/D = 2 at different radial locations along characteristic direction using hot-wire technique. The purpose of these measurements and comparison is to study the variations in the flow field with the different configurations of chevron, which might be related to the acoustic field. CN1 nozzle has a 40dB turbulent kinetic energy reduction compared to the baseline nozzle CN0, and CN2 has the highest turbulent flow field, which is a mixture of low, medium and high velocities corresponds to three directions. CN3 has the most similar mean velocity and turbulence intensity profiles, this may be caused by the under developing jet flow field.