Introduction

Abstract

Flow control involves controlling a flow field using passive or active devices in order to bring on desired changes in the behavior of the flow. For instance, laminar flow, which is characterized by parallel layers of fluid moving in a very regular and deterministic way, is associated with considerable less drag, or friction, at wall-fluid interfaces, than its counterpart, turbulent flow, which is characterized by small scale velocity components that appear to be stochastic in nature. On the other hand, turbulent flow may exhibit better mixing properties than laminar flows. Usually, laminar flows are unstable, and will unless controlled, evolve into turbulent flows. Common control objectives include [54]:

• Delaying or advancing transition from laminar to turbulent flow;

• Suppressing or enhancing turbulence, and;

• Preventing or provoking separation.