Design Of Counter-Rrotating Double-Runner Bulb Turbine And Control Of Flow Interference

Bulb turbines are originally developed for the low head application. With increasing demand of clean sustainable power, it is urgent to expand their applicable range toward a higher head for the larger power. It is difficult, however, to expand the applicable limit toward higher heads than the 20m/45MW class with the single-stage runner due to the limit of the specific speed. A new bulb turbine having the counter-rotating double-runner was researched in this dissertation, in order to substantially expand the applicable limit toward higher heads with larger power. The research required to minimizing the Euler energy interference between the frontal and rear runners with the optimum control of the adjustable vanes to secure a smooth operation.In Chapter 2, as a preliminary study, a method of performance prediction was investigated with the steady flow analysis, followed by a new method of hydraulic design of a 15m/34MW class conventional bulb turbine (BT). By providing the numerical inner interfaces at the runner inlet and outlet etc, the flow Euler energies with hydraulic loss were precisely evaluated. The flow interference between the stationary guide vanes and the rotating runner, as well as the runner and the draft tube was also investigated through the flow on the inner interfaces, to find the optimum control for a smooth operation. As a result, the on-cam performance at the optimum combination of adjustable guide vanes and adjustable runner vanes was numerically predicted before the experimental model test of time consuming. Based on the above basis of flow analysis, a new method of designing an advanced runner vane was created by optimizing the flow through the guide vanes, runner and draft tube. In conclusion, the preliminary preparation was established for the new design of counter-rotating double runner bulb turbine.In Chapters 3, a new idea of counter-rotating double-runner bulb turbine (DRT) was established by replacing the stationary guide vanes to a frontal runner (DR_f) rotating in anti-clockwise against the rear runner (DR_r) of clockwise rotation. Three inner interfaces were numerically provided to design the DRT: the inlet sliding interface in front of DR_f, the counter-sliding interface between DR_f and DR_r, and the outlet sliding interface at the exit of DR_r. A basis theory of velocity triangles was established on the three inner interfaces to share the even head and output power by the two runners under the given design discharge. As a result, the total head and output power of DRT was doubled, at a stroke without changing the unit size, compared with the conventional BT. If the given design head is unchanged, as the head for DR_r is reduced to a half, the excavating depth for a new DRT can be reduced to a half for the conventional BT.In Chapters 4, a new DRT of 30m/68MW class was designed according to the method established. The steady flow analysis of the DRT revealed that, on the counter-sliding interface between DR_f and DR_r, the Euler energy interference was not small due to the unfair blade loading from hub to tip of both runners. A quantitative evaluation method of fairness in blade loading was proposed for the combination of DR_f and DR_r.In Chapter 5, a new idea of fair blade-loading design method was established to both runners. As the result of adjusting a logical balance of supply and demand for Euler energies to DR_f and DR_r, the blade loading was optimized to keep the equilibrium of Euler energy from hub to tip. New DR_f and DR_r were optimized with the fair loading design. The steady flow analysis verified the minimum interference of Euler energy on the counter-sliding interface. The on-cam setting angles of adjustable DR_f and DR_r were predicted to control the operation of DRT smoothly. By the numerical unsteady flow analysis, the pressure fluctuations were less than 2 % of runner head under the optimum control of both runners.In conclusion, this research provided a theoretical basis for the optimal design and the flow analysis of the adjustable-vane counter-rotating double-runner bulb turbines. It is feasible to double the limit of applicable head/power to the 40m/90MW class without increasing the turbine size and the excavation depth under the smooth control of counter-rotating frontal/rear runners with the on-cam combination of adjustable runner vanes.