Linear Stability Analysis Using the Arnoldi Eigenmode Extraction Technique Applied to Separated Nozzle Flow

A linear stability analysis method, employing a linearized flow solver combined with the Arnoldi algorithm for eigenmode approximation, was applied to a separated supersonic flow inside an axially symmetric convergent-divergent nozzle. The eigenmodes were analyzed in terms of frequency, structure and damping. For the case demonstrated, four different types of axial modes and four different types of tangential modes were identified. Results show that the least damped axial modes displayed a relatively low frequency range, 60 Hz to 300 Hz. These modes showed a movement of the shock pattern inside the nozzle. The other mode types exhibited higher frequencies, strong shear layer interactions and acoustic waves. Additionally, the method revealed the presence of a continuous spectrum in the nozzle flow field