本文针对水力发电机组在运行过程中出现的影响运行稳定性的水压脉动问题进行了阐述，通过总结目前国内外模型或真机试验中尾水管压力脉动的测试和分析研究，并结合实验室前期针对此问题的研究，利用数值模拟的方法，开展了对补气抑制尾水管中低频水压脉动的深入研究。首先，针对补气工况下多相湍流数值计算方法进行了研究。结合补气后流场内存在液气汽三组分的流动特点，基于对流场内不同尺度的旋涡流动、气相带了的可压缩性以及相交界面表面张力的影响，对湍流模型和多相空化模型进行了相应的修正，充分反映了通入空气对流动发展的影响。其次，采用经翼型通气空化流动验证的计算方法，对混流式水轮机低负荷工况下产生螺旋空化涡带进行了计算。结果表明，随着空化数的降低，涡带由单一液相涡带转变为多相空化涡带，除了涡带旋转所诱发的压力脉动之外，空化涡带体积波动诱发了新的脉动。向尾水管中通入空气可以有效抑制尾水涡带所诱发的压力脉动。在较小的补气量下，能够部分抑制由涡带旋转扰动所诱发的压力脉动；当补气量较大时，尾水管内的流动特性发生本质变化，所有压力脉动均被抑制，从压力方面分析，流动变得相对稳定。同时，对补气前后尾水管内流场的流动特点进行了深入分析。结果表明，高压气体的通入能够提高涡带中心区域的压力，改善圆周速度和轴向速度的分布，减小涡带偏心距，这是小补气量下尾水管压力脉动被抑制的主要原因。随着补气量的增加，由于高压气体对压力和速度的影响以及对主流区液相的排挤，涡带脱落形式由螺旋状脱落逐渐变为柱状脱落，流场内旋涡流动特征发生了本质改变，从而抑制了压力脉动的产生。最后，对转轮顶盖补气和主轴中心孔补气进行了对比，结果表明在相同补气量工况下，顶盖补气在脉动抑制和效率优化上略优于中心孔补气。同时针对旋涡流动和压力脉动关系的认识，提出了一种带有抑涡槽的泄水锥结构，研究结果表明合理设计的抑涡槽结构能够有效降低部分负荷工况下旋涡强度从而抑制压力脉动，而对设计工况和高负荷工况的流动稳定性不产生明显的影响。

This paper introduced the flow instabilities in the operating of the hydro turbines. Based on the experiments of the model turbines or prototype turbines, numerical simulations were done to make a deep investigation of the air admission effect on the pressure fluctuations in the draft tube. Firstly, the simulation method for multiphase turbulence flow was investigated. Focus on the flow characteristics of the multiphase flow, the multiphase cavitation model and turbulence model were modified by considering the compressibility of air and the multiscale vortex. The modified simulation method was verified by comparing the simulation results with the experimental data of the ventilated cavitation around a NACA0015 hydrofoil.Secondly, the internal flow in a Francis turbine operating under partial load was simulated based on the modified simulation method. It is indicated that with the decreasing of the cavitation number, the vortex rope turned to be a vapor rope from a water rope. Besides the pressure fluctuation induced by the rotating of the vortex rope, cavitation surge also induced a pressure fluctuation. Air injected into the draft tube can alleviated the pressure fluctuations partially with a small air injected flow rate, and totally with a large air flow rate.Then, the effect of the air admission on the vortical flow in the draft tube was investigated based on the simulation results. It is indicated that the injected air can increase the pressure level of the vortex rope core, improve the distribution of the circumferential and axial velocity and minish the eccentric distance of the rope. While with the increase of the air flow rate, the injected air pushing the water away and make the vortex breakdown changed from spiral one to a cylindrical one. This is the main reason for air admission can alleviated the pressure fluctuations induced by the vortex rope.Lastly, the comparison between runner crown injection and spindle hole injection was make. It is indicated that with the same air flow rate, air injected from the runner crown more effective than injected from the spindle hole. Also a grooved runner cone was designed to alleviate the pressure fluctuations.