## 1 Introduction
They pointed out that by introducing streamwise vortices, streamwise slot control may help delay or prevent downstream separation. By solving Navier-Stokes equations enclosed by an IDDES turbulence model, [PERSON] et al. [1] investigated the influence of vortex generators with inclined angles on the transonic buffet of an OAT15A airfoil. They found that the time-averaged location of the shockwave was pushed downstream; thus, the root-mean-square of the oscillating force in the buffeting zone decreases, and the total lift is enhanced. [PERSON] et al. [36] and [PERSON] et al. [7] tested mechanical, continuous, and pulsed fluidic vortex generators located upstream from the shock foot to reduce the extent of the separated area, and fluidic actuators as well as mechanical vortex generators have proven to be very efficient in postponing buffet onset. [PERSON] et al. [37] proposed a method of using three-dimensional bumps on upper wing surfaces to alleviate the strength of flow interference between the shockwave and boundary layers, and the results indicated that a 30% decrease of total drag can be achieved for the best control case. Then, [PERSON] and [PERSON] [38] optimized the three-dimensional bump shape, and they pointed out that the bump can generate stream-wise vortices at high Mach numbers, suggesting improvement in the buffet margin. [PERSON] et al. [10; 24] studied the suppression effect of bumps on the transonic buffet. They found that the strength of the shockwave was weakened, and the location of the shockwave was stabilized; thus, buffet and drag-rise characteristics are improved. [PERSON] and [PERSON] [39] suppressed transonic shock oscillation and alleviated the buffet load for supercritical airfoils by using a micro-tab. Among the active control works on the transonic buffet, [PERSON] et al. [23; 40; 41] developed a trailing edge deflector (TED) with a close-circuit control loop to control the transonic buffet. Results showed that when the oscillating frequency of TED was close to buffeting frequency, evident control effectiveness could be obtained. The drawback of this method is that the control law for three-dimensional flow is very complicated. [PERSON] and [PERSON] [32] investigated the control effect of a 20% chord-length trailing edge flap under prescribed oscillation on transonic buffet, and they found that large, prescribed flap motions eliminated the lift resonance response and significantly reduced the lift coefficient amplitude. [PERSON] et al. [9] tested the impact of flapping rudders on the transonic buffet, and they stated that resonant rudders may be a feasible open-loop strategy to suppress buffet loads under different buffet states. [PERSON] et al. [14] tested the control effect of an upper trailing-edge flap (UTEF), and they pointed out that the UTEF prevents flow separation downstream of the shockwave, shifts the buffet boundary to higher angles of attack, and increases the lift coefficients. [PERSON] et al. [42] and [PERSON] et al. [43; 44; 45; 46] used tangential slot blowing for transonic buffet control of a P-184-158R supercritical airfoil, and they pointed out that tangential blowing can shift the shockwave downstream and increase the lift. From the published literature, it is found that by adopting passive control techniques such as slots normal to the wall, bumps and vortex generators on the upper surface, and so on, satisfactory control effects can be obtained under design conditions, while off-design conditions engender unexpected effects, and aerodynamic characteristics can even deteriorate. With the utilization of active control techniques, such as trailing edge deflectors, flapping rudders, and so on, the control law proves to be very complicated for three-dimensional flow, and the size of the control surface is relatively large; thus, large driving forces are needed, which depletes extra energy.