| The numerical study of global instability of the two dimensional flow in a model dump combustor has been conducted by solving Navier-Stokes equations. The numerical scheme used in this work is the Marker and Cell (MAC) method. To control the instability of flow in this model, distributed suction has been applied in the base of the step and results are compared with case of without suction. The interesting variables are boundary layer thickness, Reynolds number, suction flux and suction slot width. The Reynolds number, however, utilized to calculate was in the range of laminar flow which had a maximum value equal to 520.; The flow at subcritical Reynolds numbers exhibits the small amplitude oscillations in both local streamewise and cross-stream velocities. When the Reynolds number exceeds the critical value, the amplitudes of streamwise and cross stream velocities increase and have periodic form. This behavior also happens with applied suction velocity at the base of step. Furthermore, the characteristics of the bifurcation to a global instability have been studied. At sufficiently high suction velocities, the flow in the domain can be stabilized. Varying the suction slot width can also change the state of the flow from unstable to stable flow with small suction velocity.; The last aim of this work is to investigate perturbation energy levels. The perturbation energy is calculated by subtracting the average energy from its time-varying value over aspecified time and aspecified spatial domain. The average time is the period of the local global instability. The areas of interest are a varying reattachment area and a fixed area. Both of the areas have the same height but the horizontal length of reattachment area varies with the position of the reattachment point. In contrast, the fixed area has a constant horizontal length. It is worth noting that with a sufficiently high suction flux, the flow transitions to a global stability leading substantially higher levels of the perturbation energy. |
