8 Wind Tunnel ‘Concept of Proof’ Investigations in the Development of Novel Fluid Mechanical Methodologies and Devices N. Findanis and N.A. Ahmed Aerospace Engineering, University of New South Wales, Sydney, Australia 1. Introduction It may be argued that the first successful flight by the Wright brothers in 1903 would not have happened had the Wright brothers not built wind tunnels and obtained aerodynamic data in a form that could be incorporated directly in the design of an actual aircraft. The wind tunnels they built at the time were of a very crude nature, but they nevertheless demonstrated conclusively their value in the aerodynamic design loop. Immediately after the historic flight, with World War I looming, a spurt in wind tunnel construction started and they were mainly built in government-funded aeronautical laboratories of Europe in countries such as Great Britain, France and Germany to achieve technical leadership in aviation between1903 and 1914. Although, primarily designed for aerodynamic studies, the wind tunnels of today are used in a multitude of fluid mechanical investigations including aerodynamic studies. It is considered to be an essential experimental tool in fluids/aerodynamic laboratories to complement research and teaching activities around the world. Today there are wind tunnels that are designed to cater for flow field investigations ranging from very low speeds to hypersonic speeds. The purpose of this chapter, however, is not to describe the design of these wind tunnels but to highlight the significance of wind tunnel investigations in the ‘concept of proof’ investigations in the development of novel fluid mechanical methodologies and devices. The materials presented here are, therefore, entirely based on the many successful and innovative works that have been carried out by N.A.Ahmed and his research teams at the aerodynamics laboratory of the University of New South Wales that spans well over a decade and supported by substantial funding from the Australian Research Council and from industry. The chapter will start with a description of the development of novel measurement methodologies for highly three-dimensional flow fields that can be created and investigated employing a wind tunnel. In this connection the development of new methodologies for application of multi-hole pressure probes developed by the aerodynamic research group at the University of New South Wales for application in highly complex flows in wakes and in cases where reversal of flows occurs will be detailed. This will be followed by a description of the group’s works where the wind tunnel investigations have featured prominently to help advance the cause of active flow control for aerodynamic efficiency of wings for aircraft www.intechopen.com