## 1 Introduction  
To save time and energy, high-speed flights are usually done by modern, large commercial aircraft, which always cruise between Mach 0.7 and 0.9 by employing supercritical wings [1; 2; 3]. These Mach numbers fall in the typical transonic flow range; consequently, unsteady shockwave/boundary layer interactions could induce intensive, large-scale, unsteady lift, and transonic buffet will be the result [4; 5; 6; 7; 8; 9; 10]. This transonic buffet not only decreases riding comfort [11; 12], but structural fatigue could also be triggered, and disastrous accidents could even result [2; 4; 9; 13; 14; 15]. Thus, transonic buffet is deemed one of the most important factors limiting the flight envelope [2; 7; 9; 14; 16; 17], since a margin of 30% on the lift coefficient at cruising conditions must be respected by design standards [7]. To delay the buffet onset margin, alleviate buffet loads, and widen the flight envelope, a lot of effort has been devoted to the development, including unveiling buffet mechanisms [4; 8; 18; 19; 20; 21; 22], of functional control techniques [2; 7; 9; 10; 14; 16; 23; 24], and so on. Meanwhile, studies have also been conducted to improve measuring techniques employed in wind tunnel tests [25], buffet onset prediction methods [17; 26; 27], numerical simulation techniques of shock/boundary layer interactions [6; 11; 25; 28; 29; 30; 31], and so on. One of the most interesting and difficult research targets is to uncover the mechanism of transonic buffet and shock/boundary layer interactions. Among these studies, wind-tunnel tests as well as numerical simulations, stability analyses, and so on, have been conducted, and different academic viewpoints have been proposed. Although the buffet mechanism has remained inexplicable over six decades due to its complexity [2], research is in progress. For example, in the last five years, [PERSON] et al. [3] presented that frequency modulation was formed by large-scale, periodic oscillations together with secondary oscillations, where low-frequency, large-scale, periodic oscillations and higher frequency secondary oscillations are generated by buffet instability and the von Karman mode near the trailing edge of the airfoil, respectively. [PERSON] and [PERSON] [4] stated that lower-frequency results are similar to the forced-response calculations reported on two-dimensional airfoils, but the three-dimensional shock buffet at higher frequencies is linked to the presence of a global destabilizing mode. [PERSON] et al. [8] presented that the flow is most receptive to harmonic forcing on the upper surface of the profile; besides the low-frequency shock unsteadiness, the flow also exhibits medium-frequency unsteadiness linked to Kelvin-Helmholtz-type instability. [PERSON] and [PERSON] [32] pointed out that the pre-buffet aerodynamic resonance response and the change in aerodynamic characteristics are governed by the shock-induced separation phenomenon, as a separation bubble was found behind the shock in static analyses. In the meantime, investigations on control techniques for mitigating buffet loads have also been performed. This research can be roughly divided into passive control techniques and active control techniques. Passive control techniques include suction slots on upper wing surfaces, vortex generators with inclined angles, three-dimensional bumps, and so on, while research on active controls includes trailing edge deflectors, flapping rudders, and so on. In the published literature on passive control studies, [PERSON] and [PERSON] [33] examined the impact of slots ejecting airflow normal to the upper surface of a supercritical airfoil. They figured out that the typical normal shock is modified to be two shocks that form a \"\(\lambda\)\", which notably decreases the total pressure loss and delays the boundary layer separation induced by the shockwave. [PERSON] et al. [34; 35] tested the effect of streamwise slots located downstream from the airfoil on the shock/boundary layer interference.