The precessing vortex core in the draft tube of Francis turbine is investigated using entropy production method. The high-fidelity Delayed Detached Eddy Simulation (DDES) method with SST k-ω turbulence model is used to acquire the entropy dissipative components of the flow, and the Q-criterion is selected to evaluate the vortex cores inside the draft tube under different operating conditions, separately. The results show that the numerical simulation is in good agreement with the experimental data obtained from the model test. It is found that the vortex motion, separation flow and shock phenomenon are considered to be hydrodynamic factors for the formation of entropy. Furthermore, draft tube accounts for the greatest proportion of entropy production, which is ascribed to the vortex rope. Vortex rope will rotate in the same direction as the runner, but the rotational speed is lower, resulting in low frequency pressure pulsation with large amplitude in the draft tube. It is concluded that the key reason why great energy dissipation is caused in the draft tube is that the vortex rope is transporting continuously towards the downstream, especially when the turbine deviating from optimum operating point.

采用熵产生法研究了混流式水轮机尾流管中的进动涡核。具有 SST k-ω的高保真延迟分离涡模拟 (DDES) 方法湍流模型用于获取流动的熵耗散分量，并选择Q准则分别评估不同工况下引流管内的涡核。结果表明，数值模拟与模型试验得到的实验数据吻合较好。发现涡旋运动、分离流和激波现象被认为是熵形成的流体动力因素。此外，尾流管占熵产生的最大比例，这归因于涡绳。涡流绳会与转轮同向旋转，但转速较低，导致尾水管内产生幅度较大的低频压力脉动。