The aim of achieving a maximum increase in the installed capacity of a hydroelectric station located in a narrow canyon without substantial additional expenditures for construction has led to the suggestion of a two-level (two-row) layout of the units in the powerhouse [1]. With such a layout the curved draft tubes of the lower level units reach a considerable length as a comequence of having to elongate the exit cone.The mutual effect of operating units and the hydraulic conditions in the lower pool of model blocks of twolevel powerhouses with long draft tubes were investigated" at the B. E. Vedeneev All-Union Scientific-Research Institute of Hydraulic Engineering (VNIIG) [2], research department of Gidroproekt, and V NIIGidromash. The effect o2 elongating the exit cone on the efficiency and discharge capacity of the turbine, except for minor investigations at VNIIGidromash, hasnot been studied.In the study made at the department of hydropower utilization at the V. V. Kuibyshev Moscow Institute of Civil Engineering (MISI), main attention was paid to an investigation of the effect of elongating the exit cone on the operation of the turbine and on the flow characteristics in the draft tube. The maximum length of the tested model robes, 15D I (Fig. 1), exceeded the length of the tubes installed in accordance with the designs of the Chirkey and Toktogul hydroelectric stations, i.e., about 9.5I) 1.At present the prospect of using draft tubes with long exit cones is limited to designs of powerhouses with a two-level layout of the units. These designs call for the installation of Francis turbines having Q~ max = 800 liters/ see. However, it is of interest to investigate the effect of elongating the exit cone over a wider range of turbine discharges characteristic not only for Francis but also for Kaplan turbines. Therefore, power tests were carried out on a model hydraulic turbine stand with a PL 20/661-25 runner.The flow structure in the entry section of the exit cone depends on the flow characteristics at the entrance to the draft re'be and on the character of this flow transformation in the entry cone and especially in the tube elbow. In the majority of turbine operating regimes the region of flow with maximum axial velocities in the tube entrance is located on the periphery of the cross section. This distribution is retained also at the entrance to the elbow. The turn of the twisted flow in the elbow with the cro~s sections gradually expanding in plan is characterized by the fact that, owing to the effect of centrifugal forces, the zone of maximum axial velocities is located at a maximum distance from the vertical plane of symmetry, i.e., near one or the other side walls of the elbow. In the case of a positive twist of the fl0w at the entry to the tube (in the direction of turbine rotation) the maximum axial velocities occupy a region near the left (with the current) wall of the elbow. As a result the greater part of the turbine discharge enters the left part of the exit cone. In the ease of a negative twist the zo...

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