Document Type
Thesis - Open Access
Award Date
2025
Degree Name
Master of Science (MS)
Department / School
Civil and Environmental Engineering
First Advisor
Francis Ting
Abstract
The study of flow over roughness transition in an open channel is very important in the field of hydraulic engineering. Bed shear stress is the key factor in predicting sediment transport and determining the stability of hydraulic structures while flow depth, flow velocity, surface roughness are some hydraulic parameters that can affect the bed shear stress in an open channel flow. In this thesis, a detailed investigation into the development of bed shear stress in a rough-to-smooth transition is performed. Experiments were conducted on flow over a rough-to-smooth transition in an open channel flume with an M2 to S2 composite water surface profile. A non-intrusive optical technique commonly known as Particle Image Velocimetry (PIV), was used to measure the fluid velocity field at the centerline of the channel. The bed shear stress was determined from the measured flow depth and velocity using four different methods. The primary objective was to investigate the behavior of bed shear stress in flows transitioning from rough to smooth bed conditions. The second objective of this study was to compare the friction velocities obtained using different methods, with particular attention given to the region after the transition. This study found that the bed shear stress was significantly influenced by flow depth and bottom roughness. In a rough-to-smooth transition under an M2 to S2 water surface profile, the bed shear stress adjusted rapidly to the new bed condition but did not reach equilibrium until the most downstream location when the flow became uniform, while the turbulence intensities and Reynolds stress decreased with distance from the transition. For the different methods used in finding the bed shear stress on the smooth bed, the Spalding wall function and log law method yielded comparable values when a logarithmic layer was present, but the Reynolds stress extrapolation method overestimated the bed shear stress due to flow history effect from the rough bed upstream. The depth-slope method did not yield results comparable to the other methods, most likely because of side wall effects in the narrow channel.
Publisher
South Dakota State University
Recommended Citation
Kafle, Monika, "Evolution Of Bed Shear Stress in Open Channel Flow Over a Rough-To-Smooth Transition" (2025). Electronic Theses and Dissertations. 1539.
https://openprairie.sdstate.edu/etd2/1539
Rights Statement
