A model of a high-head bottom spillway with interaction of concentric swirled flows

Abstract

When designing hlgh-head spillways the provision of protection of the waterway of the structure from the destructive action of the high-velocity flow is a complex problem. It is often economically expedient to use low-head spillways as the service ones in the case of high heads and also to closely arrange or combine the power and spillway conduits. In these cases it is necessary to create conditions for dissipating the excess kinetic energy of the discharge behind the service gates to prevent cavitation erosion of the linings and scour in the lower pool, to reduce the dynamic loads on the structural elements, and to provide normal conditions of operation of the power conduits.For a number of years scientific laboratories of our country have been investigating socalled eddy spillways [i] based on the effect of swirling the flow in the exit section behind the dlscharge-regulating gate. It was established as a result of these works that when the flow is swirled the pressure increases and the wall velocities decrease as a consequence of the effect of the!~centrifugal forces on the walls of a cylindrical tunnel. This increases the cavitation safety of the spillway. The use of the interaction of swirled flows makes it possible to reliably dissipate their excess kinetic energy [2, 3].Thus the investigations showed the prospects of spillways of this type for high-head hydraulic structures [4]. An analysis of the expected technical--economical, layout, and operating characteristics shows their competitiveness and, in a number of cases, advantages over spillways of the traditional types, particularly over multilevel spillway systems [5, 6]. At present research is practically completed, considerable empirical data have been accumulated, methods of calculation hay been developed for the majority of spillways of this type, and a pilot model wlth an 800-unmdiameter exit conduit has been tested [7]. The necessary data are available for converting from research to practical introduction. However, the obstacle on this path was the complexity and labor intensity of construction and the technological inefficiency of the majority of the designs proposed by researchers.With consideration of this, at the hydrodynamics laboratory of the Moscow Special Design Department of Steel Hydraulic Structures (Mosgidrostal') investigations were aimed at developing primarily rather simple designs of bottom eddy spillways based on using the usual types of high-head sates mastered by Soviet industry: vertical-llft and radial. The possibility of realizing such a spillway system was examined in one of the publications [8]. As a result of the given work, a spillway system in which dissipation of the kinetic energy is accomplished by the interaction of concentric oppositely swirled flows was proposed and investigated on a model (Fig. 1).The spillway operates in the following way. Two flows from the entrance sections 1 enter the gate chambers with the emergency-guard 2 and service 4 gates, from under which in a free-into-air regime behind the gates (via...