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Vortex shedding behind tapered obstacles in neutral & stratified flow

Vortex shedding behind tapered obstacles in neutral & stratified flow
Vortex shedding behind tapered obstacles in neutral & stratified flow
Results of laboratory and numerical experiments on both homogeneous and density-stratified flow over single, bluff obstacles of various shapes are presented. The obstacle height is in most cases of the same order as the base diameter and the major controlling (flow) parameter is the Froude number, defined here as Fh=U/Nh, where U is the (uniform) upstream velocity, h the obstacle height and N is the buoyancy frequency. Attention is concentrated, firstly, on the case of homogeneous flows over rather weakly tapered obstacles and, secondly, for bodies whose height is similar to their base width, on the case Fh=0.1, representing stratification sufficiently strong that lee-wave motions do not play a significant role in the flow dynamics. For right-circular cones it is shown that the sectional contributions to the total fluctuating side force (lift) show significant phase variations up the height of the obstacle, which are not always reflected in the developed vortex street further downstream. For some obstacle shapes, the vortex lines linking the von Karman eddies at different heights can be significantly tilted, particularly in the upper part of the wake. Vortex convection speeds do not appear generally to vary greatly with height and, as found in previous work, the shedding frequency remains constant with height, despite the strong variation of cross-stream obstacle width. By comparison with the homogeneous results, it is suggested that the stratification enhances the shedding instability, which would otherwise be very weak for squat obstacles, but does not annihilate the ability of the flow at one level to influence that at another.
stratified flow, vortex shedding
0377-0265
145-163
Castro, Ian
66e6330d-d93a-439a-a69b-e061e660de61
Vosper, Simon
d118ba0f-d9b4-4ee1-a6b6-ef53a9d5386e
Paisley, Martin
7cb9f822-5efb-4553-8d4f-0d9c04469c00
Hayden, Paul
b5662acc-6375-4f86-afee-04c779155d5f
Castro, Ian
66e6330d-d93a-439a-a69b-e061e660de61
Vosper, Simon
d118ba0f-d9b4-4ee1-a6b6-ef53a9d5386e
Paisley, Martin
7cb9f822-5efb-4553-8d4f-0d9c04469c00
Hayden, Paul
b5662acc-6375-4f86-afee-04c779155d5f

Castro, Ian, Vosper, Simon, Paisley, Martin and Hayden, Paul (2001) Vortex shedding behind tapered obstacles in neutral & stratified flow. Dynamics of Atmospheres and Oceans, 34 (2-4), 145-163. (doi:10.1016/S0377-0265(01)00065-3).

Record type: Article

Abstract

Results of laboratory and numerical experiments on both homogeneous and density-stratified flow over single, bluff obstacles of various shapes are presented. The obstacle height is in most cases of the same order as the base diameter and the major controlling (flow) parameter is the Froude number, defined here as Fh=U/Nh, where U is the (uniform) upstream velocity, h the obstacle height and N is the buoyancy frequency. Attention is concentrated, firstly, on the case of homogeneous flows over rather weakly tapered obstacles and, secondly, for bodies whose height is similar to their base width, on the case Fh=0.1, representing stratification sufficiently strong that lee-wave motions do not play a significant role in the flow dynamics. For right-circular cones it is shown that the sectional contributions to the total fluctuating side force (lift) show significant phase variations up the height of the obstacle, which are not always reflected in the developed vortex street further downstream. For some obstacle shapes, the vortex lines linking the von Karman eddies at different heights can be significantly tilted, particularly in the upper part of the wake. Vortex convection speeds do not appear generally to vary greatly with height and, as found in previous work, the shedding frequency remains constant with height, despite the strong variation of cross-stream obstacle width. By comparison with the homogeneous results, it is suggested that the stratification enhances the shedding instability, which would otherwise be very weak for squat obstacles, but does not annihilate the ability of the flow at one level to influence that at another.

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Published date: 2001
Keywords: stratified flow, vortex shedding

Identifiers

Local EPrints ID: 22594
URI: https://eprints.soton.ac.uk/id/eprint/22594
ISSN: 0377-0265
PURE UUID: 57750f46-eed8-4da5-a5b3-0e3827bbd588

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Date deposited: 23 Mar 2006
Last modified: 17 Jul 2017 16:21

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Author: Ian Castro
Author: Simon Vosper
Author: Martin Paisley
Author: Paul Hayden

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