The onset, frequency selection, and control of nonlinear global modes in low-density jets

A low-density axisymmetric jet is studied experimentally. The onset for various density ratios is determined in the parameter space including Reynolds number and momentum thickness. A universal frequency scaling of the primary global mode is determined and encompasses several facilities and research groups. Finally different control techniques are implemented with varying degrees of success including complete suppression of the global mode and relaminarization of the unstable jet. Open-loop acoustic forcing yields a wide range of control and provides connections to theoretical underpinning of the globally unstable flow.