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Obstacle drag in stratified flow

Obstacle drag in stratified flow
Obstacle drag in stratified flow
This paper describes an experimental study of the drag of two- and three-dimensional bluff obstacles of various cross-stream shapes when towed through a fluid having a stable, linear density gradient with Brunt-Vaisala frequency, N. Drag measurements were made directly using a force balance, and effects of obstacle blockage (h/D, where h and D are the obstacle height and the fluid depth, respectively) and Reynolds number were effectively eliminated. It is shown that even in cases where the downstream lee waves and propagating columnar waves are of large amplitude, the variation of drag with the parameter K (= ND/$\pi $U) is qualitatively close to that implied by linear theories, with drag minima existing at integral values of K. Under certain conditions large, steady, periodic variations in drag occur. Simultaneous drag measurements and video recordings of the wakes show that this unsteadiness is linked directly with time-variations in the lee and columnar wave amplitudes. It is argued that there are, therefore, situations where the inviscid flow is always unsteady even for large times; the consequent implications for atmospheric motions are discussed
1364-5021
119-140
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61
Snyder, W.H.
6925a08b-cb1c-4d8e-967d-f48a4aab995c
Baines, P.G.
17775441-140e-4177-b36d-5fae642b8c04
Castro, I.P.
66e6330d-d93a-439a-a69b-e061e660de61
Snyder, W.H.
6925a08b-cb1c-4d8e-967d-f48a4aab995c
Baines, P.G.
17775441-140e-4177-b36d-5fae642b8c04

Castro, I.P., Snyder, W.H. and Baines, P.G. (1990) Obstacle drag in stratified flow. Proceedings of the Royal Society of London A, 429 (1876), 119-140. (doi:10.1098/rspa.1990.0054).

Record type: Article

Abstract

This paper describes an experimental study of the drag of two- and three-dimensional bluff obstacles of various cross-stream shapes when towed through a fluid having a stable, linear density gradient with Brunt-Vaisala frequency, N. Drag measurements were made directly using a force balance, and effects of obstacle blockage (h/D, where h and D are the obstacle height and the fluid depth, respectively) and Reynolds number were effectively eliminated. It is shown that even in cases where the downstream lee waves and propagating columnar waves are of large amplitude, the variation of drag with the parameter K (= ND/$\pi $U) is qualitatively close to that implied by linear theories, with drag minima existing at integral values of K. Under certain conditions large, steady, periodic variations in drag occur. Simultaneous drag measurements and video recordings of the wakes show that this unsteadiness is linked directly with time-variations in the lee and columnar wave amplitudes. It is argued that there are, therefore, situations where the inviscid flow is always unsteady even for large times; the consequent implications for atmospheric motions are discussed

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Published date: 1990
Organisations: Aerodynamics & Flight Mechanics Group

Identifiers

Local EPrints ID: 354303
URI: https://eprints.soton.ac.uk/id/eprint/354303
ISSN: 1364-5021
PURE UUID: 3b7c36c4-509a-475b-8a57-94edc9fb1d78

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Date deposited: 08 Jul 2013 09:16
Last modified: 15 Sep 2017 16:33

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