AMPLITUDE AND FREQUENCY MODULATION OF THE SMALL SCALES IN A TURBULENT JET

This work involves the large-scale amplitude and frequency modulation of the small-scale motions in fullydeveloped turbulence of a high Reynolds number jet. The scales responsible for the production of turbulent kinetic energy (large scales), and those responsible for its viscous dissipation (small scales) are extracted from time series of hotwire signals, using a band-pass spectral filter. The top-down interaction between the turbulent scales is then examined. We show that the strength of the large-scale fluctuations affect non-linearly the amplitude of the small-scale signal. Furthermore, the higher frequency components within the small-scale signal exhibit stronger amplitude modulation, which evidences frequency modulation. Analogies and dissimilarities with turbulent flows other than jets are discussed.