A complex-valued resonance model for axisymmetric screech tones in supersonic jets

We model the resonance mechanism underpinning generation of A1 and A2 screech tones in an under-expanded supersonic jet. Starting from recently proposed by \cite{mancinelli2019screech}, where upstream-travelling wave is a neutrally-stable guided jet mode, we here present more complete linear-stability-based for prediction. study temperature shear-layer thickness effects show that, order to accurately describe experimental data, effect finite shear layer must be incorporated jet-dynamics model. then improved screech-frequency predictions which both downstream- waves may have complex wavenumber frequency. This requires knowledge reflection coefficients at upstream downstream locations loop. explore on propose approach their identification. The complex-mode identifies limited regions frequency-flow parameter space loop amplified time, necessary condition sustained. provides description measurements.