Passive Fluidic control of flow around circular cylinder

Suction of the boundary layer is an effective means of delaying separation and reducing drag on external flows. However, if a pumping system is required to generate the suction, the weight and power consumption of the system can undo that benefit. ‘Autogenous’ (self-generating) suction control is a type of flow control that utilises the energy already within a flow (notably the pressure gradients) to drive the suction, thereby requiring no further energy to the system. This paper describes numerical studies that were performed on the flow around the circular cylinder in the 2D laminar range: Re = 40 (steady) and Re = 120 (unsteady). Suction and blowing control were implemented by imposed velocity boundary conditions. These controls were then modified using optimisation methods to generate arrangements of suction and blowing that can be passively generated by their pressure differential (i.e. Ps ≥ Pb). Steady and unsteady simulations were performed. It was found that at both Re = 40 and Re = 120 drag-reducing arrangements could be produced. At Re = 120 a reduction in drag of 4.3 % was found while maintaining a positive pressure differential from the suction to blowing loci. This approach for developing passive suction control can be applied to other bluff body flows and higher Reynolds numbers to design efficient optimised flow control although specifics of the control parameters may be slightly different.