Aerodynamics of bluff bodies has gained the attention of aerodynamicists all over the world in recent times, primarily because of importance given to drag reduction by the automobile industry. Since pressure drag accounts for bulk of the drag of bluff bodies, any technique to manipulate and control the overall pressure field around such bodies to achieve base pressure rise causes reduction of drag. Interestingly, not many works are found on 3- dimensional bluff bodies such as spheres. Currently, interest in spherical airships is growing, triggered by the tourism industry. However, the high drag and management of highly unsteady wake of spheres are some of the aerodynamic issues that need to be addressed. This book offers the concept of passive natural ventilation as a potential solution. Natural ventilation occurs when the stagnation zone and the base are interconnected through an internal duct, which causes a jet flow through the center. Based on several years of experimental research, it is shown that natural ventilation of a sphere leads to substantial drag reduction and reduced wake unsteadiness at high Reynolds numbers.

Gargeshwari K Suryanarayana, PhD: Studied Aerospace Engineering at Indian Institute Science, Bangalore, Scientist at the National Aerospace Laboratories, Bangalore, India, Received many citations based on publications in Experiments in Fluids, Journal of Visualization, AIAA and IUTAM Conferences. Honorary Advisor, DAAD, Bonn.