Numerical and experimental study of discrete trapped acoustic waves

We report on the latest results from our experimental-numerical collaboration to find discrete trapped acoustic waves in turbulent jets. In high subsonic jets, it is well-known that the mean flow supports resonance modes in certain frequency bands (Towne et al. J. Fluid Mech. vol. 825, 2017; Schmidt et al. J. Fluid Mech. vol. 825, 2017; Jordan et al. J. Fluid Mech. vol. 853, 2018). Perhaps lesser-known is that within each narrow frequency band, the modes are hypothesized to be spectrally discrete. Our ongoing effort had previously produced clear evidence of these discrete modes in large-eddy simulation data. A new experimental campaign involving time-resolved schlieren imaging has now corroborated these findings. We compare the trapped waves yielded by numerical simulations and experiments to the predictions of linear theory.