Spatially developing turbulent boundary layer on a flat plate

TL;DR

This study visualizes the development of a turbulent boundary layer on a flat plate towed through water, revealing fundamental processes and large-scale structures as it evolves from trip to high Reynolds number.

Contribution

It provides a unique visualization method for observing the full evolution of turbulent boundary layers in a stationary frame, which is difficult in traditional experiments.

Findings

Visualization of boundary layer evolution from trip to high Reynolds number

Observation of large-scale coherent structures as nearly stationary in the flow frame

Insights into processes like interfacial bulging, entrainment, and vortical motions

Abstract

This fluid dynamics video submitted to the Gallery of Fluid motion shows a turbulent boundary layer developing under a 5 metre-long flat plate towed through water. A stationary imaging system provides a unique view of the developing boundary layer as it would form over the hull of a ship or fuselage of an aircraft. The towed plate permits visualisation of the zero-pressure-gradient turbulent boundary layer as it develops from the trip to a high Reynolds number state ($Re_\tau \approx 3000$). An evolving large-scale coherent structure will appear almost stationary in this frame of reference. The visualisations provide an unique view of the evolution of fundamental processes in the boundary layer (such as interfacial bulging, entrainment, vortical motions, etc.). In the more traditional laboratory frame of reference, in which fluid passes over a stationary body, it is difficult to observe the full evolution and lifetime of turbulent coherent structures. An equivalent experiment in a wind/water-tunnel would require a camera and laser that moves with the flow, effectively `chasing' eddies as they advect downstream.