| Abstract: |
A study of scour downstream sudden expanding stilling basin was investigated. Different cases were studied to show the effect of different variables on scour characteristics. The analysis of the experimental data and the statistical analysis lead to the following conclusions:I-The rate of scouring is very high at the first few minutes then the rate of scouring slows down with the further increase of time. This means that a high percentage of scours occurs during the short-term scour and the small ratio occurs during the long-term scour process. The relationship between the scour depth and time was presented by equation (6.1). The relationship between the scour volume and time is satisfied by equation~- The scour downstream of the sudden expanding stilling basins with or without end sill is asymmetric. The magnitude of scour depth and scour pattern are function of Fa, e, h/G, G/Hu and D501G, where the lower expansion ratio produces smaller values of the maximum scour depth and vice versa.-The presence of end sill changes the flow pattern slightly upstream of the sill and highly just downstream of the end sill.,-The height of end sill should be designed carefully to improve the scour pattern and to produce the minimum scour depth. From the experimental study, for e=2.5 the use of relative sill height h/G=O.68-1.45 gives minimumd/G values and for e=2.0 and 1.54 the use of h/G =0.0 gives minimum diG values in general followed by h/G=0.68.5-The extent of scour and deposition processes (dm, Ls, Lm) depends on F G, e and h/G for a particular soil type.5-The empirical equation (6.5) can be used for scour estimation for an apron with an end sill of sloped up stream face (2: 1) and vertical one at the downstream side with different sill heights.7•Using the asymmetric side sill significantly reduced the maXImum scour depth and the extent of scour and deposition processes when usmg a single or double system of sills. The effect of using double asymmetric side sills on reduction of the scour and deposition processes was more effective than using a single side sill. For FG <3.0, the use of X/Lb=(0.25, 0.5) produces lower values of d/G while the system X/Lb =(0.5,0.75) is more effective for FG>3.0. Both systems produce lower extent of scour and deposition to about 50% or even•Simple prediction equations are developed to estimate the maximum relative scour depth downstream SESB with asymmetric one or two side sills, equation (6.6).-Using two symmetric side sills in the SESB affects the flow pattern over the solid apron and hence scour DS of SESB was affected. The . scour and deposition are mostly symmetrical around the centerline of the flume regardless of its magnitude.the symmetric sills that minimizes the and reduces the scour anddeposition processes is a function of F G, hs, W siB and angle (e) for a particular soil type. Within the experimental conditions of this study, the scour depth decreases by constructing two-side sills at. X)Ln=O.l5-0.5 rather than flat apron case and increases by increasing X)Lb to 0.75. The sills at X/Lb=0.35 causes maximum reduction in scour depth to about 43% and shorten the extent of scour and deposition to about 65% and produces more smooth water surface with less fluctuations.II-The use of two side sills with lateral length more than 60% of the flume width enhances the flow patterns and the maximum scour depth was remarkably reduced to about 59.4% and the length over which the scour and deposition processes takes place was significantly shortened to about 63%.12- The scour depth decreases as the sill height increase to a certain values (h/G=O.O to 2.0) then any increase in sill height increase the scour depth at particular location and lateral width of the sill. The use of side sill angles ranges between 90°<120° decreases the scour depth greatly to about 39%. Also the scour and deposition processes end at shorter distances about 50% compared to no sill case.13-Simple prediction equation was developed to estimate the maximum relative scour depth DS of SESB with symmetric side sills.1- Study the stability of another types of riprap particles with different shapes, sizes and densities are needed.2- Further studies are required to apply the obtained scour depth equation for one vent regulator on multi-vent regulators (asymmetric expansion).3- The study proposes a similar investigation for slopping floors and also for Froude numbers higher than 4.5.4- Studying the effect of curved side sills on scour processes. Also, further studies are required to apply the effect of continuos sill on scouring and deposition process.5- The same work is proposed to be done for the submerged hydraulic jump below abrupt expansions.••6- Studying the shear stress and velocity distribution is recommended for riprap design.
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