DOI: 10.1615/TSFP9
An experimental study of the role of core intermittency in equivalent jet noise sources
SINOPSIS
Large-scale turbulence intermittency has been found in previous work to have a large impact in the noise emission of high speed jets. In the current study, turbulence intermittency due to motions originating from the irrotational core of heated supersonic jets is investigated. A novel multipoint Doppler Global Velocimetry (DGV) instrument with a frequency resolution of 125 kHz is employed to obtain time-resolved data of velocity fluctuations. For jet total temperatures of 1.6 and 2.0 times the ambient temperature, results from the perfectly-expanded supersonic jets at 1.65 isentropic exit Mach number help confirm key observations of convective wave speeds in these flows. In particular, it is apparent that the core region for the colder jet remains irrotational up to 10 diameters downstream of the nozzle exit−the region observed in the study. The hotter case exhibited centerline intermittency of approximately 0.4-0.6 for the stations examined at 6, 8, and 10 diameters downstream the nozzle exit. The results provide a first examination of the interplay of density ratio effects and the dynamic breakdown process of the potential core in supersonic jets−physics integral to the noise generation process.