We present a conditional space–time proper orthogonal decomposition (POD) formulation that is tailored to the eduction of rare or intermittent events. By construction, the resulting spatio-temporal modes are coherent in space and over a finite time horizon, and optimally capture the energy of the flow. For the example of intermittent acoustic radiation from a turbulent jet, we extract the statistically loudest event from high-fidelity simulation data. Our formulation identifies the statistically most significant ‘prototype’ burst event and tracks its evolution over time. We investigate the underlying mechanism using linear stability theory and find that its structure and evolution are accurately predicted by optimal transient growth theory.

The empirical ‘prototype’ burst event and the optimal transient growth prediction are compared side-by-side in the video.

Literature:

• Schmidt, O. T. and P. J. Schmid. “A conditional space–time pod formalism for intermittent and rare events: example of acoustic bursts in turbulent jets.” Journal of fluid mechanics 867 (2019): R2.
  [Bibtex]

  @Article{SchmidtSchmid_2019_JFMR,
  author = {Schmidt, O. T. and Schmid, P. J.},
  title = {A conditional space–time POD formalism for intermittent and rare events: example of acoustic bursts in turbulent jets},
  journal = {Journal of Fluid Mechanics},
  year = {2019},
  volume = {867},
  pages = {R2},
  doi = {10.1017/jfm.2019.200},
  file = {:SchmidtSchmid_2019_JFM.pdf:PDF},
  publisher = {Cambridge University Press},
  }