In 1904, one year before Einstein published his miraculous papers, Ludwig Prandtl proposed the revolutionary concept of a boundary layer. This idea, in one shot, bridged the gap between the classical disciplines of “hydraulics” and “hydrodynamics” and gave birth to the modern discipline of “fluid dynamics” as we study it today. In this talk, I will present the basic physical idea, its consequences and the mathematical preliminaries which constitute what is now called the “boundary-layer theory”.
Boundary layers appear in myriad forms in aeronautical flows. In the second half of this lecture, I will talk about the structure of a “turbulent” boundary layer, which contributes to nearly half of the frictional drag experienced by a typical passenger aircraft during cruise. It is believed that the major contributors to the skin friction in a turbulent boundary layer are the “coherent motions” and a great deal of research is being carried out to understand their origin and dynamics. I will try to provide glimpses of some of the recent research advances made in this area.
