COMPACTNESS OF HYDRAULIC JUMP RECTANGULAR STILLING BASINS USING A BROAD-CRESTED SILL

B. ACHOUR, L. AMARA, D. MEHTA, P. BALAGANESAN

Abstract


The study looks at the possibility of reducing the length of a rectangular hydraulic jump stilling basin by setting up a broad-crested sill. The conclusions of the study are based exclusively on laboratory tests using a specially designed hydraulic installation. The sills tested meet the hydraulic and geometric conditions of broad-crested sills suggested by the literature, in particular the Rao and Muralidhar study of 1963. The dimensionless parameters involved in the problem are the relative sill height S = s/h1, the relative length of the stilling basin X/h1 corresponding also to the relative position of the sill, and the Froude number F1 of the incident flow of depth h1. However, experimentation shows that the relative length X/h1 of the basin depends only on one of the parameters S or F1. An explicit experimental relationship between the three parameters involved X/h1, S and F1 is derived, bearing in mind that S and F1 are related by a theoretical relationship according to a previous study conducted by the authors. The experimental tests involve the following wide ranges: 1 £ S £ 6.15, 18 £ X/h1 £ 60, and 3.082 £ F1 £ 9.20, which allow drawing quality conclusions.

The compactness of the stilling basin is evaluated by the ratio X/Lj*, where Lj* is the length of the classical hydraulic jump evolving freely on a horizontal apron without a sill. The sequent depth ratio Y* = h2*/h1 of this type of hydraulic jump is related to the incident Froude number F1 by the well-known Belanger’s theoretical relationship successfully demonstrated in 1828, which remains unchanged.

Using the obtained appropriate experimental dimensionless relationship, combined with the Bradley and Peterka experimental equation giving the length of the classic hydraulic jump, it is shown that the ratio X/Lj* is always less than unity regardless of the value of the Froude number F1. This fact clearly indicates that the setup of a broad-crested sill has a reducing effect on the length X of the stilling basin. An in-depth study of the variation curve of X/Lj* against F1 reveals that the best compactness is obtained for F1 = 7.311, giving X/Lj*» 0.765, which corresponds to a compactness rate of 23.5%.


Keywords


Control of hydraulic jumps, classical hydraulic jumps, CHJ, compactness, rectangular stilling basins, broad-crested sills, incident Froude number

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References


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