The role of shape and relative submergence on the structure of wakes of low-aspect-ratio wall-mounted bodies

The role of shape and relative submergence on the structure of wakes of low-aspect-ratio... The effects of shape and relative submergence (the ratio of flow depth to obstacle height, d/H) are investigated on the wakes around four different low-aspect-ratio wall-mounted obstacles at Re H  = 17,800: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, and two cylinders with aspect ratios matching the ellipsoids (H/D = 0.89 and 0.67, where D is the maximum transverse dimension). Particle Image Velocimetry was used to interrogate the flow. Streamwise features observed in the mean wake include counter-rotating distributions of vorticity inducing downwash (tip structures), upwash (base structures), and horseshoe vortices. In particular, the relatively subtle change in geometry produced by the rotation of the ellipsoid from the streamwise to the transverse orientation results in a striking modification of the mean streamwise vorticity distribution in the wake. Tip structures are dominant in the former case, while base structures are dominant in the latter. A vortex skeleton model of the wake is proposed in which arch vortex structures, shed from the obstacle, are deformed by the competing mechanisms of Biot-Savart self-induction and the external shear flow. The selection of tip or base structures in the ellipsoid wakes is caused by tilting of the arch structures either upstream or downstream, respectively, which is governed by ellipsoid curvature. An inverse relationship was observed between the relative submergence and the strength of the base structures for the ellipsoids, with a dominant base structure observed for d/H = 1 in both cases. These results demonstrate a means by which to achieve significant modifications to flow structure and thereby also to transport mechanisms in the flow. Therefore, this work provides insight into the modeling and control of flow over wall-mounted bodies. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

The role of shape and relative submergence on the structure of wakes of low-aspect-ratio wall-mounted bodies

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Publisher
Springer Journals
Copyright
Copyright © 2012 by Springer-Verlag Berlin Heidelberg
Subject
Engineering; Engineering Thermodynamics, Heat and Mass Transfer; Fluid- and Aerodynamics; Engineering Fluid Dynamics
ISSN
0723-4864
eISSN
1432-1114
D.O.I.
10.1007/s00348-012-1406-1
Publisher site
See Article on Publisher Site

Abstract

The effects of shape and relative submergence (the ratio of flow depth to obstacle height, d/H) are investigated on the wakes around four different low-aspect-ratio wall-mounted obstacles at Re H  = 17,800: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, and two cylinders with aspect ratios matching the ellipsoids (H/D = 0.89 and 0.67, where D is the maximum transverse dimension). Particle Image Velocimetry was used to interrogate the flow. Streamwise features observed in the mean wake include counter-rotating distributions of vorticity inducing downwash (tip structures), upwash (base structures), and horseshoe vortices. In particular, the relatively subtle change in geometry produced by the rotation of the ellipsoid from the streamwise to the transverse orientation results in a striking modification of the mean streamwise vorticity distribution in the wake. Tip structures are dominant in the former case, while base structures are dominant in the latter. A vortex skeleton model of the wake is proposed in which arch vortex structures, shed from the obstacle, are deformed by the competing mechanisms of Biot-Savart self-induction and the external shear flow. The selection of tip or base structures in the ellipsoid wakes is caused by tilting of the arch structures either upstream or downstream, respectively, which is governed by ellipsoid curvature. An inverse relationship was observed between the relative submergence and the strength of the base structures for the ellipsoids, with a dominant base structure observed for d/H = 1 in both cases. These results demonstrate a means by which to achieve significant modifications to flow structure and thereby also to transport mechanisms in the flow. Therefore, this work provides insight into the modeling and control of flow over wall-mounted bodies.

Journal

Experiments in FluidsSpringer Journals

Published: Nov 10, 2012

References

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