Input-output modes and their relevance to jet noise reduction of supersonic jet flows from bi-conical nozzles.*

Input-output analysis is used to describe the radiated noise of the shock-laden, supersonic exhaust generated by an axisymmetric bi-conical jet nozzle. Large-eddy simulations (LES) are used to predict the unsteady, turbulent jet at a fixed nozzle pressure ratio (NPR) of 4 and three total temperature ratios (TTR) of 1, 3, and 7. The non-modal, input-output analysis is performed about each time-averaged base flow, providing the optimal linear forcing and corresponding response modes, using a singular value decomposition of the input-output operator. Additionally, sub-optimal modes associated with a smaller gains are also computed. The physical relevance of the resulting modes are evaluated through projection onto the unsteady data. Sensitivities of the gains to the TTR are measured and compared with analytical predictions.