CLARK B. MILLIKAN Lecture in Aerospace
Logarithmic scaling is one of the cornerstones of our understanding of wall-bounded turbulent flows. In 1938, Clark B. Millikan advanced an overlap argument that framed the logarithmic variation of the mean velocity in simple dimensional terms. Seventy-five years later, however, basic aspects of this logarithmic region, such as its slope (described by von Karman's constant) and its spatial extent are still being debated. In addition, Townsend in 1976 proposed a logarithmic scaling for the streamwise and spanwise components of turbulence based on the attached eddy hypothesis, but to date the experimental verification has been elusive. Here, we use pipe flow measurements over a very large Reynolds number range to examine these expectations of logarithmic scaling, and show that pipe flows at sufficiently high Reynolds number reveal both expected and unexpected implications for our understanding and our capacity to model turbulence.