Non-Uniform Suction Control of Flow around a Circular Cylinder

In the present study, numerical investigations were performed with optimisation to determine efficient non-uniform suction profiles to control the flow around a circular cylinder in the range of Reynolds numbers 4<Re<188.5. Several objectives were explored, namely the minimisation of: the separation angle, total drag, and the pressure drag. This was in an effort to determine the relationships between the characteristics of the uncontrolled flow and the parameters of optimised suction control. A variety of non-uniform suction configurations were implemented and compared to the benchmark performance of uniform suction. It was determined that the best non-uniform suction profiles consisted of a distribution with a single locus and compact support. The centre of suction on the cylinder surface for the optimised control, and the quantity of suction necessary to achieve each objective, varied substantially with Reynolds number and also with the separation angle of the uncontrolled flows. These followed predictable relationships, however. Non-uniform suction profiles were much more efficient at eliminating boundary layer separation, requiring the removal of less than half the volume of fluid as uniform control to achieve the same objective. Regardless of the method of control, less net suction was needed to minimise total drag than to eliminate separation. Though boundary layer separation could always be prevented, its elimination did not always result in an improvement in total drag, and in some circumstances increased it.