Effect of tailwater on jet scour

• Main Author: Ee, Man Ting
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/154393
• Institution: Nanyang Technological University

Scour is a natural phenomenon that removes excessive excavated sediments around the structures located in the flow of water. For jet scour, understanding the difference and analysis of jet scour caused by 2D and 3D horizontal jet scour has been studied recently by a few earlier FYPs in NTU. In these studies, the tailwater depth was found to be an important parameter, and its effect on jet scour is explored further in this study. An existing database consisting of 518 experimental results was available and the effect of tailwater depth on jet scours was investigated by specifically focussing on data that were conducted under a wide range of tailwater depths. Dimensional analysis was used to identify the characteristic parameters affecting the scour formation. The regression feature in the Excel tool was used to obtain the computed Standard Error, SE and coefficient of determination, R2 for the data using the multiple regression model. Both SE and R2 provide a numerical assessment of how well a regression model fits the sample data. By observations and interpretation on the graphical plots, the effects of several characteristic parameters were evaluated. The analysis concluded that the densimetric Froude number F0,d84 based on sediment size d84, has better prediction ability compared to that based on the commonly used densimetric Froude number F0,d50 with sediment size d50. Furthermore, the analysis also showed that the scour prediction improves by adding the sediment size term d50/Rh to the tailwater depth term (1+ H/Rh). A predictive maximum scours equation with a higher correlation coefficient of R2 compared to earlier studies was obtained. For practical purposes, a new equation,Dse/Rh =0.869Fo,d84^(1.002+0.033 ln⁡(d50/Rh ) ) x 1+H/Rh ^(-0.1129+0.024 ln⁡(d50/Rh)), was proposed for deeply submerged jet outlet condition with the relative tailwater H/Rh > 10.