Homage to Bob Brodkey at 85: Ejections, Sweeps and Reynolds Shear Stress Generation in Turbulent Pipe Flow

TL;DR

This paper revisits Brodkey and Corino's classic visualization study of turbulent pipe flow near the wall, highlighting ejections and sweeps as key mechanisms in Reynolds shear stress generation across different Reynolds numbers.

Contribution

It presents a fluid dynamics video showcasing original visual sequences at three Reynolds numbers, emphasizing the historical and scientific significance of the original experiments.

Findings

Ejections account for 70% of Reynolds shear stress at Re_d=20,000.

Ejections occur about 18% of the time in turbulent flow.

Visual sequences illustrate the structure of near-wall turbulence phenomena.

Abstract

Almost 50 years ago Bob Brodkey and his student, Corino, conceived of and carried out a visualization experiment for the very near wall region of a turbulent pipe flow that, together with the turbulent boundary layer visualization of Kline et al., excited the turbulence research community. Using a high speed movie camera mounted on a lathe bed that recorded magnified images in a frame of reference moving with the flow, they observed the motions of sub-micron particles in the sub-, buffer- and log-layers. Surprisingly, these motions were not nearly so locally random as was the general view of turbulence at the time. Rather, connected regions of the near wall flow decelerated and then erupted away from the wall in what they called "ejections". These decelerated motions were followed by larger scale connected motions toward the wall from above that they called "sweeps". They estimated that ejections accounted for $70\%$ of the Reynolds shear stress at $Re_d = 20,000$ while only occurring about $18\%$ of the time. This fluid dynamics video shows short sequences, at three Reynolds numbers, from the original Corino and Brodkey visual study. In the following decades it inspired numerous laboratory and simulation studies aimed at unraveling the structure of bounded turbulent flows and understanding the turbulent transport processes within them.