Resolvent analysis on the origin of two-dimensional transonic buffet

TL;DR

This study uses resolvent analysis to uncover the origin of transonic buffet over an airfoil at low Reynolds number, revealing shock foot perturbations as the source and expanding understanding of buffet mechanisms.

Contribution

The paper demonstrates that resolvent analysis can identify buffet origins at low Reynolds numbers, highlighting shock foot perturbations as the key source.

Findings

Buffet can occur at low Reynolds numbers with appropriate forcing.

Shock foot is the primary source of buffet in the analyzed flow.

Resolvent modes validate the identified buffet mechanism.

Abstract

Resolvent analysis is performed to identify the origin of two-dimensional transonic buffet over an airfoil. The base flow for the resolvent analysis is the time-averaged flow over a NACA 0012 airfoil at a chord-based Reynolds number of 2000 and a free-stream Mach number of 0.85. We reveal that the mechanism of buffet is buried underneath the global low-Reynolds-number flow physics. At this low Reynolds number, the dominant flow feature is the von Karman shedding. However, we show that with the appropriate forcing input, buffet can appear even at a Reynolds number that is much lower than what is traditionally associated with transonic buffet. The source of buffet is identified to be at the shock foot from the windowed resolvent analysis, which is validated by companion simulations using sustained forcing inputs based on resolvent modes. We also comment on the role of perturbations in the vicinity of the trailing edge. The present study not only provides insights on the origin of buffet but also serves a building block for low-Reynolds-number compressible aerodynamics in light of the growing interests in Martian flights.