水利水電畢業(yè)設(shè)計(jì)外文文獻(xiàn)翻譯-橋梁設(shè)計(jì)(編輯修改稿)
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【文章內(nèi)容簡(jiǎn)介】 stigations, since it is still not possible to evaluate all the elements of the operation of a spillway by means of calculations. Thus, let us turn our attention to a number of theoretically important problems. A familiarity with these topics will be of assistance in the design and investigation of vortex spillways. Evaluation of the Design and Geometric Dimensions of the Elements of a Spillway. The selection of a particular type of spillway depends on a number of factors, such as the effective head, the magnitude of the escapage discharge, the configuration of the hydraulic project (for example, the use of a river diversion tunnel during the operational period or of the water conduits of hydroelectric power plants in the construction period), conditions in the discharge of the flow into the tailrace channel, topographic and geological features (in particular, the possible length of the tailrace leg), and the technical and economic characteristics. Inlet (entry segment in the form of surface or subsurface offtake). The inlet is designed on the basis of standard techniques to maintain its conveyance capacity when functioning in the freefall regime. Shafts (vertical or inclined). The diameter of the shaft is made nearly equal to the diameter of the tailrace leg: It should be noted that the eddy node is designed so that A = Areq, where Are q is the value of the geometric parameter of the vortex generator needed to maintain the required prerotation of the flow. For example, for the conditions of the Tupolangskii vortextype spillway, Are q = 。 for the Tel39。mamskii hydraulic works, Are q = 。 and for the Rogunskii spillway, Ar:q = . A second parameter which characterizes the degree of rotation of the flow on individual legs of the tailrace segment is the integral flow rotation parameter II [1, 2]. The prerotation 17 0 behind the vortex generating device at a distance from the axis of the shaft may be determined on the basis of graphical dependences thus: 17_o = f(A) (Fig. 4).Tailrace tmmd. The overall widths of the tunnel are determined by the type of spillway design which is selected and the method decided on for dissipation of the excess energy (either by means of smooth or increasingly more intensive dissipation). Energy Dissipation Chamber. The choice of design and dimensions depends on the rate of rotation of the flow at the inlet to the chamber and on the length of the tailrace tunnel following the chamber. For a tailrace tunnel with LT/d T _ 60, it is best to use a converging tube (or cylindrical) segment as the conjugating element between the tangential vortex generator and the energy dissipation chamber. The segment will be responsible for the following functions: reduction of the rate of rotation of the flow at the inlet to the energy dissipation chamber, equalization of flow rates acpanied by a shift in the maximum axial ponent of the flow rate into the central portion, and reduction of the dynamic loads at the rotation node of the flow. From the foregoing discussion it follows that in those cases in which there is no entrapment of air, vortex spillways may be modeled with respect to all the required criteria. The situation is different in the case of aerated flow, which is also difficult to model. In hydraulic models with external atmospheric pressure, the volumetric content of air varies slightly as the flow is transported down the shaft to the critical section, whereas in the physical structure, the entrapped air, moving downwards, is pressed by the increasing pressure of the liquid. Thus, in the case of the spillway at the Teri hydraulic works (Fig. 1), the percent pression in the physical structure is as much a
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