Diffusion of the Sluice Way Jet
When a stream passes under a submerged sluice gate into water on the downstream side, it forms a jet which goes far downstream before it is dispersed [1]. A knowledge of the behaviour of such a jet is of engineering importance because it allows designers
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Diffusion of the Sluice Way Jet S.K. Al Naib North East London Polytechnic
INTRODlICTION When a stream passes under a submerged sluice gate into water on the downstream side, it forms a jet which goes far downstream before it is dispersed [1]. A knowledge of the behaviour of such a jet is of engineering importance because it allows designers to predict the rate of deceleration of the jet which is necessary in the prevention of scour downstream of hydraulic structures Furthermore, it leads to a better understanding of the mechanism of turbulent diffusion of jets in restricted spaceso Although it was one of the classical problems in hydraulic~ it has been little studied in the pasto Early publications mainly describe model tests for guiding design and predicting the depths and heads associated with the discharge characteristics. Consequently the correlations were given in terms of one-dimensional forms of continuity, momentum and energy relationships [2]. 0
The approach followed by these investigators has been, in general, empirical in character concerning an overall study of the flow variables. While information of this type is essential for industrial design, it does not lead far towards a fundamental understanding of the flow mechanism o However, when as in the present investigation the details of flow are examined a definite picture emerges of the jet dispersing in the deeper water downstream, in the manner occurring in other diffusion problems and conforming with similar statistical picture. Only a little relevant work has yet been published. Liu [3] investigated by pitot-cylinder the mean patterns with different depths of water downstream. He found that the distance required for the jet to diffuse in a given depth is independent of the Froude number. By using a pitot-tube operating an electrical circuit, Henry [3] measured the longitudinal component of turbulence in certain of the patterns previously K. V. H. Smith et al. (eds.), Hydraulic Design in Water Resources Engineering: Land Drainage © Springer-Verlag Berlin Heidelberg 1986
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studied by Liu. He discovered that the energy of the turbulence is less than one per cent of the energy of the mean flow. Their results contained discrepancies such as the one between the measured discharge and that calculated through the integration of the velocity profiles. Rajaratnam [4] attempted to analyse the jet as the case of a plane turbulent wall jet under an adverse pressure gradient over which a backward flow has been placed. He presented the forward flow simply as a plane wall jet and evaluated the backward flow using the results of Liu and Henry. The two parts were joined to predict the characteristics of the jet. Unfortunately, the theoretical profiles did not compare at all with the measured surface profiles, either in shape or magnitude [5]. The above three works, while containing some unexplained discrepancies, nevertheless clearly contribute to a better understanding of the general flow pattern. As a further contribution, the present investigation was unde
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