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INVESTIGATION OF SUBMERGED INLETS TO DEEP
RECTANGULAR SLUICES
N. P. Rozanov, N. Ya. Konakhovich,
and L. N. Orlova UDC 532.522.001.5

The form of the inlet to deep sluices should be selected to meet the following conditions: 1) cavitation does not occur; 2) on changing to a pressure flow from a free flow or vice versa unfavorable transitional regimes do not arise in the sluice, and the pressure remains stable; 3) the dimensions of the inlet bellmouth be as small and its outlines as simple as possible. The last condition can be the reason for allowing some vacuum at the inlet (not causing cavitation), especially if measures are taken to prevent a periodic sucking in of air into the vacuum region through vortices which form in the upper pool, and a stable pressure regime of the pipe is ensured [2].
Inlets of different shapes are used, depending upon local conditions: a sluice length, its position relative to the river bed, bottomslope, inclination of the upstream face of the structure, etc. Sluices with a vertical upstream face of structure have been investigated more than those with an inclined face. Round inlets [3] and certain types of elliptical inlets [4] have been rather thoroughly investigated, although only time-averaged pressures on the inlet without consideration of their fluctuations have been studied. Other streamlined inlets, shaped with respect to the coordinates of the surface of the stream discharging from an opening in a thin wall, can be used. In this case the inlet should be practically vacuum-free and with a very small (in this case even zero) length of conduit [4]. Since the shapes of these inlets depend on the ratio H/a. where H is the pressure head, a is the height of the pipe, which does not remain constant, they were replaced by inlets close to elliptical in shape. The inclination of the upstream face of the structure and the slope of the bottom of the conduit noticeably affect the outlines of a "vacuum-free"inlet corresponding to the discharge of a fluid through an opening in a thin wall (Fig. 1). As applied to bottom conduits,
experimental or theoretical coordinates of the surface of the stream discharging from under a shield can be used directly for constructing the upper and side outlines of the inlet walls; in the presence of a sill and an inclined face of the structure, they can be used approximately (Fig. 2). We see from Fig. 2 that for hydraulic structures the shape of the floor, ceiling, and side walls of the inlet could be made different and that it is necessary to form most smoothly the ceiling of the conduit, since it is here that a maximum vacuum is possible with the presence of an unfavorable form. The curves in the corners of the cross sections of the inlet are eliminated to reduce the vacuum[4].
Efficient inlets will be different in different cases.in some cases the surfaces of the inlet will be outlined quite smoothly (short pipes operating at high velocities)
and in others more compressed, simpler forms of inlets are acceptable.
Results are presented below of investigations of inlets of various structures with deep openings carried out recently at the department of hydraulic structures of the V, V. Kuibyshev Moscow Civil Engineering Insititute.
Theoretical Determination of the Shape of Vacuum-Free Inlets. The shapes of the inlets to undersluices can be obtained by using the theory of fluid motion, largely developed by N. E. Joukowsl[1].Examining the discharge of a fluid from a vesselbounded
by two plane symmetric walls (Fig. 8a), N. E.Joukowski derived as an equation of the contour BCD of the stream an equation to which we can give the form:


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