Active flow control around simplified 3D bluff bodies

In the present work is illustrated a flow control technique designed with the aim of reducing the aerodynamic drag of a three-dimensional car model with a square-back rear part. The technique is based on continuous jets disposed in the periphery of the rear surface of the model. The design process of the entire investigation is illustrated. As a first step, a preliminary CFD study was performed to verify the effectiveness of the technique and its sensitivity to the flow control parameters. This CFD analysis assisted the design and the set up of the physical experiment. Several different measurements were performed and the entire chain of measurement is widely described evidencing the methodology. The assessment of this experimental methodology is also presented, which allowed to properly calibrate the different acquisition parameters and to reach adequate level of accuracy and repeatability of the measurements. Subsequently, the experimental investigation with the several diagnostic measurements allowed to understand and explain the flow characteristics. The wide range of flow control configurations evidenced, in fact, the effect that the forcing have on the pressure distribution, the flow structures and, consequently, on the drag value. The wake different sensitivity on the flow control parameters highlighted the most effective configuration which led to a drag reduction up to 12.6%. The analysis of pressure fluctuations, supported by the smoke visualization and the POD analysis evidenced the main flow structures present in the wake, their typical frequencies and their relation on the drag values. Finally the energy budget of the entire flow control system is presented in order to highlight the most efficient configurations and evidence the multi-criteria aspect of the active flow control technique presented.