Steady and unsteady coupling in twin weakly underexpanded round jets

Tsz Y.M. Wong, Michael N. Stavropoulos, Jayson R. Beekman, Aaron Towne, Petrônio A.S. Nogueira, Joel Weightman, Daniel M. Edgington-Mitchell

Research output: Contribution to journalArticleResearchpeer-review

3 Citations (Scopus)


We investigate the intermittency of the coupling behaviour in screeching twin round supersonic jets at low Mach numbers across a range of nozzle spacings. Application of proper orthogonal decomposition combined with time-frequency wavelet analysis and spectral proper orthogonal decomposition shows that intermittency can manifest in twin jets as either a competition between the two symmetries, or the jets uncoupling and recoupling. The time scales on which symmetry switching occurs can vary strongly, ranging from to screech cycles. A transition from one symmetry to another is accompanied by a slight change in the screech frequency ranging from 0.30 % to 0.63 %. It was observed that complete uncoupling occurred only at the largest nozzle spacing of and at Mach numbers close to modal staging. When the jets are uncoupled they screech at slightly different frequencies, with a disparity of approximately 0.6 %. The coupling is particularly intermittent in the transition from the A1 to A2 branch, where the A2 mode is first observed, and tends toward steady coupling with increasing Mach number.

Original languageEnglish
Article numberA2
Number of pages43
JournalJournal of Fluid Mechanics
Publication statusPublished - 10 Jun 2023


  • aeroacoustics
  • flow-structure interactions
  • supersonic flow

Cite this