Bluff Body Aerodynamic Drag Reduction by Active Flow Control

摘要

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 fundamentalcornerstone of a larger research program aimed at similar objectives but focusingon 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 andmanipulation of the natural vortex shedding regime, which was achieved by theSuction and Oscillatory Blowing (SaOB) fluidic actuator, as part of thedevelopment of a new active flow control device for heavy vehicles’ aerodynamicdrag reduction and fuel savings.The experiments were carried out at Reynolds number range between 50,000and 250,000, with smooth or rough model surface conditions. Several key aspectsof the AFC system operation and its interaction with external-flow to becontrolled were tested. Among the parameters that were studied we can mentionthe number of actuators used along the span of the model, which directly affectthe energetic efficiency of the system and the influence of different actuationparameters such as the excitation magnitude, its frequency, suction distributionand phase relations between adjacent actuators. Optimal operational conditionswere identified. These lead to significant drag reduction (up to 60%), completesuppression of the vortex shedding and increased overall system efficiency, byabout 15%. The three-dimensional spanwise structure of the flow was examinedand successfully utilized for enhanced energy efficiency.