Two-dimensional numerical investigations of flow characteristics behind a circular cylinder in the presence of a flapping plate mounted in the wake have been carried out in the present study. The flapping frequency of the plate has been varied in the range from 0.6 to 1.4 times the vortex shedding frequency behind single stationary circular cylinder in the presence of a stationary plate. The gap between the cylinder and the plate is considered to be 1D, 2D and 3D. The maximum amplitude of the tip of the plate has been fixed to be 0.3D (D being the diameter of the cylinder) for each of the frequency ratio for fixed value of Reynolds number (Re) equal to 100. The length of the plate has been chosen equal to cylinder diameter. The dynamic effects and the behaviour of vortex shedding behind the cylinders have been studied elaborately. Effect of fixed amplitude and varying frequency ratio of the cylinder on wake flow behaviour has been presented in the form of vorticity contours, lift, drag and Strouhal number (St) plots. The dynamic forces as well as the flow structure behind the plate are found to be modified in the presence of the flapping plate. © 2016 Avestia Publishing.