Title

Effects of submergence and test startup conditions on local scour by plane turbulent wall jets.

Date of Award

2004

Degree Type

Thesis

Degree Name

M.A.Sc.

Department

Civil and Environmental Engineering

First Advisor

Balachandar, R.

Keywords

Engineering, Civil.

Rights

CC BY-NC-ND 4.0

Abstract

Experiments were carried out to study the interaction of plane turbulent wall jets with cohesionless soils during scour. The jet of water having a constant mean velocity of 1.16 m/s and thickness of 25.4 mm at the nozzle exit was set to initially flow tangentially along the sand bed with a median grain size of 2.15 mm. Both scour profile measurements and velocity measurements were obtained for a range of submergences, defined by the ratio of the tailwater depth to the nozzle opening. The results confirm the presence of two distinct types of flow fields, one that occurs at lower submergences and the other at higher submergences of the jet. At low submergences, laser Doppler anemometer measurements indicate that the jet flow is initially close to the bed and then flicks towards the water surface, whereas at the higher submergences, no such flicking movement was noticed. At higher submergences, however, the jet impingement point on the sand bed was highly unsteady. Low pass filtering of the velocity data give further details of these processes. It is seen that the movement of the impingement point for high submergences is more rapid with decreasing submergence. Furthermore, variations in scour and velocity profiles were noted in the mound region across the flume cross-section, and were found to be dependent on the level of submergence. In an effort to clarify some of the differences noted in the scour characteristics in earlier studies, the test startup conditions were varied. This includes an instantaneous, a gradual and a stepwise startup condition. The velocity measurements indicate that the flow gradually evolves to a state that is independent of the startup conditions. However, the scour profiles appear to be dependent on the startup conditions for a longer period of time.Dept. of Civil and Environmental Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2004 .D47. Source: Masters Abstracts International, Volume: 43-03, page: 0915. Advisers: Ram Balachandar; K. Mazurek. Thesis (M.A.Sc.)--University of Windsor (Canada), 2004.