School of Mechanical Engineering, Faculty of Engineering, Tel-Aviv University, Tel-Aviv, Israel Baseline and controlled flow around a circular cylinder at transitional Reynolds numbers were measured and simulated. Active flow control in the form of slot and holes suction was applied to delay boundary layer separation with the aim of reducing form-drag. The first target of the study was to quantify form-drag reduction as a result of delay of boundary layer separation using slot suction with velocity ratio about unity. Once this has been quantified, the slot was replaced with an array of holes with similar total cross section. It was found that holes provided about 15 degrees of separation delay, as did the slot, at similar flow conditions. Detached eddy simulations were applied at the exact experimental conditions, using periodic boundary conditions in the spanwise direction. Generally good agreement was found between experiment and CFD results, while certain discrepancies are discussed. A discussion of fundamental flow physics provided by the detailed CFD data is also included.