Author(s): Rocio Leslie Arista Alarcon
Linked Author(s):
Keywords: Localized scour; Experimental
Abstract: The results obtained on the research of localized scour phenomena due to a horizontal water jet that flows submerged over a rigid apron towards a movable bed of non-cohesive soil are presented. The jet is produced by the flow through a sluice gate and submergence is controlled regulating the level of water downstream of this gate. A theoretical analysis has been done based on several studies of localized scour phenomena developed by other researchers, and tests have been executed on a physical model specially designed which permitted verification of the hypothesis outlined. The variables manipulated during the tests are: length of the rigid apron, sluice gate opening, mean velocity of the horizontal water jet as it is issued through the sluice gate, depth of submergence, and movable bed characteristics. Even if at first it was considered that the movable bed soil would be represented by two parameters: geometric mean and geometric standard deviation from this mean of the grains that compose the sediment mixture, tests have strengthen, the same as in other research works, that non uniform mixtures may be represented solely by the d95 diameter. Otherwise, tests verified that the length of the rigid apron has only the effect of attenuating the jet velocity since the flow pattern over the apron is that of a diffusion jet with physical behavior similar to that of a free jet. Then, knowing the decrease of velocity due to the length of the rigid apron, the case may be treated as one of a horizontal jet without a rigid apron previous to the movable bed. This reasoning allowed simplification on the treatment of experimental data and it was found possible to obtain a unique relation between dimensionless parameters which would describe the case studied and also indicate which are the variables that reign the process of localized scour downstream of a sluice gate with rigid apron. The function obtained is intimately related to the analysis presented by Marion Carstens in 1966 who evaluated several cases of localized scour introducing the sediment number which is practically equivalent to the densimetric particle Froude number used nowadays. It has been found during the tests some dependence of the scour on the depth of submergence, though its effect has not been studied.
Year: 2005