The aerodynamic behaviour of transonic flow around a supercritical aerofoil is strongly influenced by shock-wave/boundary-layer interaction (SBLI) due to compressible and viscous effects. SBLI causes undesirable effects in various manners including flow instability, drag rise, and buffet, which crucially limit the flight envelop hence operation. In this paper, a numerical investigation is conducted for an OAT15A supercritical aerofoil under a typical buffet onset condition. Unsteady Reynolds-Averaged Navier-Stokes (URANS) equation is used to simulate the compressible, viscous flowfield. A two-dimensional (2D) surface bump based on preceding research on SBLI control is employed as a flow control device. It is placed on the suction side of the aerofoil relative to the shock position, with a fixed location of 27% of the chord length. A freestream condition of Mach 0.73 and a 3.5° angle of attack have been considered for the unsteady flowfield. It has been found that the trailing edge vortices within the separation bubble have considerable influence on self-sustained shock oscillation by scrutinising the flowfields in the presence/absence of bump control. The establishment of a λ-shock structure effectively restricts the motion of the front shock leg without incurring significant re-expansion generated by the moving rear shock leg. This subsequently suppresses flow separation at the trailing edge within an acceptable range, and attenuates the periodic lift fluctuation associated with the oscillating shock movement.