尾水管深度对轴流定桨式水轮机性能的影响

尾水管深度对水轮机的效率及稳定性都有重要影响。为解决某电站水轮机效率及出力不足的问题,采用数值模拟的方法,分析了尾水管深度变化对水轮机性能的影响。通过几个不同尾水管加深方案的比较分析,得出尾水管深度在一定范围内增加能有效提高尾水管回能系数,降低扩散损失。但由于沿程摩擦损失会随深度增加而增大,因而综合考虑损失、效率及经济性因素,最终选定尾水管深度为3.0D1的尾水管深度方案。同时,为保证水轮机的运行稳定性,也比较了该方案对流场稳定性的影响,分析了湍动能及脉动的变化。结果表明尾水管与转轮内流场存在相互作用,直锥段加高后不但会降低直锥段出口的湍动能,也会减轻转轮出口的湍动能。即尾水管内流动的改善也会降低转轮出口附近流场的紊乱程度,显著降低了转轮所受到的径向力及压力脉动峰峰值,提升了转轮内流场的稳定性。此外尾水管深度改变方案对转轮空化性能的影响不大,转轮叶片背面的最低压力范围基本没有变化。

Effect of Draft Tube Depth on Performance of Axial Flow Fixed-blade Turbine

The performance of draft tube plays an important role in the efficiency and stability of hydraulic turbine. To improve the hydraulic performance of an axial flow fixed-blade hydro-turbine, the depth of draft tube was studied by changing the draft tube cone height using numerical simulation. Three different modified cases of draft tube depth were conducted and analyzed. The results showed that the recovery coefficients and the diffusion losses of draft tube were increased with its depth increasing within limits. However, the fraction losses were decreased with it. Thus, the draft tube depth of 3.0 D 1 was chosen as the initial scheme by comprehensive consideration of the efficiency and economic factors. Besides, the turbulence kinetic energy, pressure fluctuations and force components acting on the runner were compared to judge the effect of draft tube depth on stability. The results showed that the increase of depth was favorable for the flow field stability at rated conditions. The turbulence kinetic energy at both the inlet and outlet of the cone was reduced with the heightening of draft tube cone, which also proved the flow field interaction between the draft tube and runner. The flow improvement in draft tube would in turn reduce the disturbance to runner outlet, which also explained the decreases of the peak to peak value and force components in runner. The areas lower than the critical cavitation pressure on the suction side of blades was almost unchanged compared with the original draft tube.