Bluff body aerodynamic drag reduction by active flow control

A simple, innovative, highly efficient and robust active flow control (AFC) system was applied to a circular cylinder, an archetype bluff-body configuration, with the purpose of drag reduction and wake stabilization. This is a fundamental cornerstone of a larger research program aimed at similar objectives but focusing on more realistic engineering applications such as heavy ground vehicles, rotorcraft, buildings subjected to cross-winds, underwater structures and more. The current study is focused on drag reduction by separation delay and manipulation of the natural vortex shedding regime, which was achieved by the Suction and Oscillatory Blowing (SaOB) fluidic actuator, as part of the development of a new active flow control device for heavy vehicles' aerodynamic drag reduction and fuel savings. The experiments were carried out at Reynolds number range between 50,000 and 250,000, with smooth or rough model surface conditions. Several key aspects of the AFC system operation and its interaction with external-flow to be controlled were tested. Among the parameters that were studied we can mention the number of actuators used along the span of the model, which directly affect the energetic efficiency of the system and the influence of different actuation parameters such as the excitation magnitude, its frequency, suction distribution and phase relations between adjacent actuators. Optimal operational conditions were identified. These lead to significant drag reduction (up to 60%), complete suppression of the vortex shedding and increased overall system efficiency, by about 15%. The three-dimensional spanwise structure of the flow was examined and successfully utilized for enhanced energy efficiency.