  Within the transonic regime, the aeroelastic problems exhibit many unique
characteristics compared with subsonic and supersonic cases. Although a lot of
research has been carried out in this field, the underlying mechanisms of these
complex phenomena are not clearly understood yet, resulting in a challenge in
the design and use of modern aircraft. This review summarizes the recent
investigations on nonclassical transonic aeroelastic problems, including
transonic buzz, reduction of transonic buffet onset, transonic buffeting
response and frequency lock-in phenomenon in transonic buffet flow. After
introducing the research methods in unsteady aerodynamics and aeroelastic
problems, the dynamical characteristics as well as the physical mechanisms of
these phenomena are discussed from the perspective of the fluid mode. In the
framework of the ROM (reduced order model) -based model, the dominant fluid
mode (or the eigenvalue) and its coupling process with the structural model can
be clearly captured. The flow nonlinearity was believed to be the cause of the
complexity of transonic aeroelasticity. In fact, this review indicates that the
complexity lies in the decrease of the flow stability in the transonic regime.
In this condition, the fluid mode becomes a principal part of the coupling
process, which results in the instability of the fluid mode itself or the
structural mode, and thus, it is the root cause of different transonic
aeroelastic phenomena.
