Modal Decomposition Analysis of Three-Dimensional Transonic Buffet Phenomenon on a Swept Wing

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Modal Decomposition Analysis of Three-Dimensional Transonic Buffet Phenomenon on a Swept Wing

Ohmichi, Yuya / Ishida, Takashi / Hashimoto, Atsushi

The dominant fluid structures and unsteady behavior of the three-dimensional transonic buffet phenomenon on a swept wing are clarified. This paper focuses on a well-established buffet phenomenon rather than an incipient shock buffet (buffet onset). Zonal detached-eddy simulation reproduced the features of three-dimensional buffet. Three-dimensional fluid structures were extracted as modes with dynamic mode decomposition. To apply dynamic mode decomposition to the large fluid dataset, the dimensionality was reduced using incremental proper orthogonal decomposition bases. Then, dominant modes were identified using the compressed sensing approach. The results showed that the computed flowfield is dominated by two fluid structures. One is a buffet cell structure oscillating at Strouhal numbers $S t$ 0.2 to 0.6. The buffet cells are spatially periodic in the spanwise direction. They are generated at midspan, where a large flow separation occurs, and they propagate at an angle toward the wing tip. The other main fluid structure has a frequency $S t \approx 0.06$ and represents the disturbances generated by the separation at midspan and propagating toward the wing tip and root. The two-dimensional shock wave at the root is oscillated by this disturbance.