Correlations and wavelet based analysis of near-field and far-field pressure of a controlled high speed jet

Discussed within are the experimental results obtained via simultaneous near-field and far-field measurements of a controlled jet. A large database of both open-loop and closed-loop control cases are carried out. The two most interesting investigations from the open-loop (OL) and closed-loop (CL) studies are highlighted here and compared to the uncontrolled jet. For the open-loop forcing, the shear layer is seeded with an axisymmetric sinusoidal input with a frequency of 1700 Hz. For the closed-loop case, the shear layer is seeded with a sinusoidal forcing amplitude modulated with the mode-filtered near-field pressure sampled from the stream-wise location at x/D = 6. Data analysis looks at both averaged and instantaneous quantities. In an averaged sense the introduction of control significantly modifies the characteristics of the developing shear layer. Open-loop control is shown to modify the phase lag between both near-field stations with a penalty in an increase in the overall sound pressure level. The closed-loop control imparts more subtle changes to the flow field but yields a slight reduction in the acoustic pressure at the microphone closest to the jet axis. Wavelet based filtering exposes the evolution of the broadband intermittent events seen at both stations.