Effect of flexible beds on flow stability in open channels

Hatata, Ahmed M (1964) Effect of flexible beds on flow stability in open channels. MSc(R) thesis, University of Glasgow.

Abstract

A brief review is given of the available theoretical and experimental work of Nonweiler end Kramer relating to the effect of surface flexibility on the maintenance of laminar flow in water. This thesis describes the results of tests on a sample of a thin sheet of soft rubber used as a bed for an open channel. The influence of this flexible bed on the stability of flow in open channels is discussed with special reference to the effect of delaying transition from laminar to turbulent flow. To this end, two criteria analogous to those of Nonweiler - the one for the elimination of the Tollmien-Schlichting waves, and the other for the elimination of the flexural waves - are applied to the consideration of the effects of possible changes in the bed material (to melinex for exampled). Transition was inferred from measurements of the friction coefficient and Reynolds number. The experimental procedure for measuring the friction coefficient and Reynolds number is discussed, and also the experimental 1 imitations which affected the measurements (hydraulic jump, and uneveness of the rubber bed for example). Owing to the limitations of accuracy, a statistical analysis for the results had to be applied in order to find the most probable values of Reynolds number for transition. It was found that if the 90% probability level is considered, the flow is likely to be laminar at a value of Reynolds number of about P2U, transitional at a value of Reynolds number between 1600 and 1800, and turbulent at a value of Reynolds number equal to 2370. It seemed doubtful whether the flexible bed used, maintained the laminar flow, when compared with rigid beds having the same shape. The material used for the bed may be thought, perhaps, to be so thin that flexural waves exist; this seemed to be indicated by gross instabilities observed in the flow when the bed was tensioned enough to ensure that the whole width of the channel was wetted. Other flexible materials are suggested which are thought probably to have better stabilizing effect on the flow.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Additional Information: Adviser: T RF Nonweiler
• Keywords: Fluid mechanics
• Date of Award: 1964
• Depositing User: Enlighten Team
• Unique ID: glathesis:1964-73966
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73966