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An experimental investigation of coherent substructures associated with turbulent spots in a laminar boundary layer

An experimental investigation of coherent substructures associated with turbulent spots in a... <jats:p>Longitudinal and transverse components of the velocity were simultaneously measured for various vertical locations at 20 off-centreline positions in turbulent spots artificially generated in a zero-pressure-gradient laminar boundary layer. Global ensemble-averaged velocity diagrams and vertical vorticity contours were computed in similarity coordinates ξ = (<jats:italic>x</jats:italic> − <jats:italic>x</jats:italic><jats:sub>0</jats:sub>)/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) and ζ = <jats:italic>z</jats:italic>/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) for different heights η = <jats:italic>y</jats:italic>/δ* above the plate. This global averaging technique inadequately describes the spot, which is not a single large vortex structure. A discriminative averaging technique was developed to construct a ‘statistically most-probable’ spot with sufficient resolution to include some of the largest substructures detected in visual studies. Four eddies were identified in vertical slices of the central region of the spot, while several rows appeared in the plan view. These features of the velocity and vorticity contours of the statistically most-probable spot exhibit similarities with structures observed in flow visualizations.</jats:p> http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Fluid Mechanics CrossRef

An experimental investigation of coherent substructures associated with turbulent spots in a laminar boundary layer

Journal of Fluid Mechanics , Volume 148: 319-348 – Nov 1, 1984

An experimental investigation of coherent substructures associated with turbulent spots in a laminar boundary layer


Abstract

<jats:p>Longitudinal and transverse components of the velocity were simultaneously measured for various vertical locations at 20 off-centreline positions in turbulent spots artificially generated in a zero-pressure-gradient laminar boundary layer. Global ensemble-averaged velocity diagrams and vertical vorticity contours were computed in similarity coordinates ξ = (<jats:italic>x</jats:italic> − <jats:italic>x</jats:italic><jats:sub>0</jats:sub>)/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) and ζ = <jats:italic>z</jats:italic>/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) for different heights η = <jats:italic>y</jats:italic>/δ* above the plate. This global averaging technique inadequately describes the spot, which is not a single large vortex structure. A discriminative averaging technique was developed to construct a ‘statistically most-probable’ spot with sufficient resolution to include some of the largest substructures detected in visual studies. Four eddies were identified in vertical slices of the central region of the spot, while several rows appeared in the plan view. These features of the velocity and vorticity contours of the statistically most-probable spot exhibit similarities with structures observed in flow visualizations.</jats:p>

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Publisher
CrossRef
ISSN
0022-1120
DOI
10.1017/s0022112084002378
Publisher site
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Abstract

<jats:p>Longitudinal and transverse components of the velocity were simultaneously measured for various vertical locations at 20 off-centreline positions in turbulent spots artificially generated in a zero-pressure-gradient laminar boundary layer. Global ensemble-averaged velocity diagrams and vertical vorticity contours were computed in similarity coordinates ξ = (<jats:italic>x</jats:italic> − <jats:italic>x</jats:italic><jats:sub>0</jats:sub>)/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) and ζ = <jats:italic>z</jats:italic>/(<jats:italic>U</jats:italic><jats:sub>∞</jats:sub>(<jats:italic>t</jats:italic>−<jats:italic>t</jats:italic><jats:sub>0</jats:sub>)) for different heights η = <jats:italic>y</jats:italic>/δ* above the plate. This global averaging technique inadequately describes the spot, which is not a single large vortex structure. A discriminative averaging technique was developed to construct a ‘statistically most-probable’ spot with sufficient resolution to include some of the largest substructures detected in visual studies. Four eddies were identified in vertical slices of the central region of the spot, while several rows appeared in the plan view. These features of the velocity and vorticity contours of the statistically most-probable spot exhibit similarities with structures observed in flow visualizations.</jats:p>

Journal

Journal of Fluid MechanicsCrossRef

Published: Nov 1, 1984

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