Small scale 3D jet scour

• Main Author: Nuramirah Suyin Zaihan
• Other Authors: Lim Siow Yong
• Format: Final Year Project
• Language: English
• Published: 2014
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/61186
• Institution: Nanyang Technological University

Numerous studies have been conducted on scouring in a laboratory setting and most of them have been centered on the idea of providing and proposing a realistic estimate to the scour formed. Nevertheless, we are ultimately concerned about the applicability and impact that these experiments have in the real world. Furthermore, it is vital for engineers to not over-estimate or under-estimate the scour formed. This is because over-estimation of scour may result in costly scour protection measures while under-estimation of scour may result in failure of bridge structures. Large scaled experiments on scour were common in various past studies with experimental conditions of a culvert pipe diameter, measuring as big as 900mm. On the other hand, not many studies have been focused and conducted on scour at a smaller scale. Therefore, this study was proposed to investigate the effects of a small scaled water jet produced from a small diameter culvert pipe. The purpose was to analyze the 3D equilibrium scour produced from this water jet. The objective of this study was to determine the relationship between densimetric Froude number (Fo) and the equilibrium scour hole geometry; maximum scour depth (dse), maximum scour length (Lse), maximum scour width (Wse) and maximum scour volume (Vse). It was to also examine the possibility of scale effect, whether the scour hole geometry was affected by scaling the experiment. An experiment was set up in the hydraulics laboratory and experimental runs were conducted to study the scour phenomenon. Data collected from these experimental runs were compared against an existing database of 347 data points. Dimensionless relationships between the scour hole geometry (d_se/d_o ,W_se/d_o , L_se/d_o and V_se/d_o ) and densimeric Froude number (Fo) were also determined. Analysis of the compiled data points suggests that the scour hole geometry was influenced by the sediment size of the bed material (d50), the mean velocity of jet at culvert pipe outlet (Uo) and the tailwater depth (Ho). Generally, the scour hole geometry increases as the densimetric Froude number (Fo) increases. It was also suggested that laboratory-based scour predictive models will most likely over-predict the prototype scour depth. Thus, indicating the likelihood of scale effect between idealized laboratory experiments to that for field conditions.