Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

Pressure fluctuation at the vaneless space and vanes passages is one of the most important problems for the stable operation of a pump turbine.The fluctuation appears in any operating condition.Much research has been done on the pressure fluctuation of hydraulic machinery.However,the details of pressure fluctuation propagation of the pump turbine at the pump mode have not been revealed.The modern pump turbine with high water head requires the runner to be"flat",which would induce pressure fluctuation more easily than the low head pump turbine.In this article,a high head pump turbine model is used as the research object.As the pressure fluctuation at off-design point is more serious than at the design point,the low head condition is chosen as the research condition.Pressure fluctuation at the vaneless space and vanes passages is predicted by the computational fluid dynamics method based on k-?shear stress transport model.The experiment conducted on the test rig of the Harbin Institute of Large Electrical Machinery is used to verify the simulation method.It proves that the numerical method is a feasible way to research the fluctuation under this operating condition.The pressure fluctuation along the passage direction is analyzed at time and frequency domains.It is affected mainly by the interaction between the runner and vanes.In the circumferential direction,the influence of the special stay vane on the pressure fluctuation is got.The amplitude in the high-pressure side passage of that vane is lower than that in the other side.The study provides a basic understanding of the pressure fluctuation of a pump turbine and could be used as a reference to improve the operation stability of it.

Investigation of the unstable flow phenomenon in a pump turbine

Instability of pump turbine with S-shaped curve is characterized by large fluctuations of rotational speed during the transient processes.For investigating this phenomenon,a numerical model based on the dynamic sliding mesh method(DSSM)is presented and used to numerically solve the 3D transient flow which is characterized by the variable rotation speed of runner.The method is validated by comparison with measured data for a load rejection process in a prototype pump turbine.The results show that the calculated rotation speed agrees well with the experimental data.Based on the validated model,simulations were performed for the runaway process using an artificially assumed operating condition under which the unstable rotation speed is expected to appear.The results confirm that the instability of runner rotational speed can be effectively captured with the proposed method.Presented results include the time history profiles of unit flow rate and unit rotating speed.The internal flow characteristics in a typical unstable period are discussed in detail and the mechanism of the unstable hydraulic phenomenon is explained.Overall,the results suggest that the method presented here can be a viable alternative to predict the dynamic characteristics of pump turbines during transient processes.

Investigation on reversible pump turbine flow structures and associated pressure field characteristics under different guide vane openings

The use of reversible pump turbines(RPT) within pumped storage power plants goes with prolonged periods of off-design operating conditions, which leads to the onset of operating mode-dependent instabilities. In order to decrease the gravity of RPT flow instabilities and associated damages or even completely eliminate them, a deep understanding of its onset and development mechanism is needed. In line with this, the present study seeks to numerically investigate the onset and development mechanism of RPT unsteady flow structures as well as the evolutional characteristics of associated pressure pulsations throughout the RPT complete flow passage, under off-design conditions for three GVOs namely 17, 21, and 25 mm. The study results showed that low torque operating conditions and associated vaneless space back flow structures were the trigger of flow unsteadiness onset within the RPT vaneless space, the instabilities which grew to cause the S-shape characteristics appearance. Moreover, the runner flow unsteadiness was found to decrease with the GVO increase. On the other hand, the GVO increase worsened the pressure pulsation levels within RPT flow zones, where pressure pulsations within the vaneless space and flow zones in its vicinities were found to be the most sensitive to GVO changes.

非线性双圆盘转子-密封系统的数值分析(英文)

研究目的:求解双圆盘转子-密封系统的非线性振动特性和运动响应创新要点:采用有限元法(FEM)和拉格朗日方程求解双圆盘转子-密封系统,进而为研究多级转子系统的非线性振动问题提供有效方法。研究方法:基于有限元法(FEM)和拉格朗日方程,得到包含Muszynska非线性密封流体力和圆盘重力作用下的双圆盘转子-密封系统的运动方程。同时利用四阶龙格-库塔法求解系统动特性运动响应情况,利用分岔图、时间历程图、轴心轨迹图、庞加莱映射和幅值谱等分析图研究双圆盘转子-密封系统的非线性振动特性。重要结论:随着转速的增大,双圆盘转子-密封系统呈现丰富的非线性运动形式,包括周期性运动、多周期运动、准周期运动以及混沌运动。在右端圆盘不平衡质量小于34 kg、密封间隙范围为0.376 mm–0.54 mm、密封长度大于0.13 m或者密封压差高于0.104 MPa的情况下均有利于提高双圆盘转子-密封系统的稳定性。