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Peter S. Bernard
Department of Mechanical Engineering
University of Maryland
Mushroom shaped vortices composed of vortex filaments erupt outward from the region adjacent to a solid boundary as the flow (toward the viewer) transitions from a smooth, laminar state towards one that is chaotic and turbulent. The vorticity contained within the filaments enters into the flow at the wall surface as a result of frictional forces near the boundary that slows the movement of the fluid. The view in the figure is the end stage of a process that first begins with a streamwise buckling of the nominally well ordered array of filaments due to a fundamental flow instability.
Proceeding downstream, the furrow-like disturbances in the filaments grow in height forming simple arches that further evolve into mushroom-like shapes as they eject toward the outer flow. The furrows collect slow moving fluid into long streaks that travel outward with the mushroom-like vortices, contributing to an important exchange of high and low momentum that is one of the most significant affects of turbulent fluid motion.
This work was supported by NSF through teragrid resources provided at the Pittsburgh Supercomputing Center.
A preliminary account of this work appeared as AIAA Paper 2009-3547 at the 19th Computational Fluid Dynamics Conference in San Antonio, Texas, June 1009. A revised and updated version of this paper is currently under review at the AIAA Journal.
The picture is not published. Reporters can freely use this image. Credit: Peter Bernard.