试验水头和空化系数对混流式水轮机尾水管压力脉动影响的试验研究

本文通过试验方法研究了模型试验水头和空化系数对混流式水轮机为尾水管压力脉动的影响。首先在混流式水轮机6个典型运行工况,即空载、低部分负荷(叶道涡)、部分负荷、最优工况、额定工况和超负荷工况进行变水头和变空化系数试验。试验结果表明在试验范围内,水头对混流式水轮机尾水管压力脉动幅值影响较小;而在一定范围内,空化系数对混流式水轮机尾水管压力脉动有较大影响。通过对部分负荷和超负荷工况幅值和频率分析发现,空化系数不仅对混流式水轮机尾水管压力脉动幅值有较大影响,对其频率分布也有较大影响。最后比较了以转轮中心线为空化基准面的压力脉动试验结果和以锥管中心线为空化基准面的压力脉动试验结果。研究表明,以转轮中心线为空化基准面进行压力脉动试验比较合理,故进行混流式水轮机压力脉动相似性研究时,需考虑空化系数的差异和空化基准面的选择。

蒲石河抽水蓄能电站1号机转轮改造水力稳定性研究与实践

蒲石河抽水蓄能电站自运行以来,机组和厂房振动强烈,给电站带来较大的安全隐患,迫切需要采取措施降低振动。为解决该振动问题,经现场测试数据分析,认为引起水电站厂房100Hz异常振动和噪声的主要激振力是由动静干涉诱发引起的。因此采用了9叶片转轮更换为7叶片转轮的错频降振改造措施。本文通过数值计算、模型试验和真机现场测试等方法,重点比较了7叶片转轮与原9叶片转轮的无叶区压力脉动幅值和现场振动情况。模型试验结果表明,经水力优化,7叶片转轮无叶区压力脉动幅值整体低于原9叶片转轮;同时,改造后原型机现场运行情况表明,机组和厂房异常振动消失,机组振摆、噪音及振动水平均大幅降低,证明了该方案的有效性和可行性,研究成果可应用到具有相同振动问题的抽水蓄能电站的改造中。

Entropy Production Analysis for Hump Characteristics of a Pump Turbine Model

The hump characteristic is one of the main problems for the stable operation of pump turbines in pump mode.However,traditional methods cannot reflect directly the energy dissipation in the hump region.In this paper,3D simulations are carried out using the SST k-ω turbulence model in pump mode under different guide vane openings.The numerical results agree with the experimental data.The entropy production theory is introduced to determine the flow losses in the whole passage,based on the numerical simulation.The variation of entropy production under different guide vane openings is presented.The results show that entropy production appears to be a wave,with peaks under different guide vane openings,which correspond to wave troughs in the external characteristic curves.Entropy production mainly happens in the runner,guide vanes and stay vanes for a pump turbine in pump mode.Finally,entropy production rate distribution in the runner,guide vanes and stay vanes is analyzed for four points under the 18 mm guide vane opening in the hump region.The analysis indicates that the losses of the runner and guide vanes lead to hump characteristics.In addition,the losses mainly occur in the runner inlet near the band and on the suction surface of the blades.In the guide vanes and stay vanes,the losses come from pressure surface of the guide vanes and the wake effects of the vanes.A new insight-entropy production analysis is carried out in this paper in order to find the causes of hump characteristics in a pump turbine,and it could provide some basic theoretical guidance for the loss analysis of hydraulic machinery.

Numerical investigation on the “S” characteristics of a reduced pump turbine model

The performance of a reversible pump turbine with S-shaped characteristics is of great importance to the transition processes such as start-up and load rejection. In order to predict the S-shaped curve accurately and develop a reliable tool for design improvement, a shear stress transport model (SST) with various numerical schemes for pressure term in the governing equation was investigated in a whole pump turbine including spiral casing, stay vanes, guide vanes, runner and draft tube. Through the computation, it was shown that different zones in the curve should employ different schemes to get the solution converged. Comparison of discharge-speed performance showed that good correspondence is got between experimental data and CFD results. Based on this, internal flow analysis was carried out at three typical operating points representing turbine mode, shut-off mode and reversible pump mode, respectively. According to the flow field concerned, the mechanism for the speed-no-load instability was explained, which provides good guidelines to take countermeasures in future design.

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.

Numerical predictions and stability analysis of cavitating draft tube vortices at high head in a model Francis turbine

Draft tube vortex is one of the main causes of hydraulic instability in hydraulic reaction turbines,in particular Francis turbines.A method of cavitation calculations was proposed to predict the pressure fluctuations induced by draft tube vortices in a model Francis turbine,by solving RANS equations with RNG k-turbulence model and ZGB cavitation model,with modified turbulence viscosity.Three cases with different flow rates at high head were studied.In the study case of part load,two modes of revolutions with the same rotating direction,revolution around the axis of the draft tube cone,and revolution around the core of the vortex rope,can be recognized.The elliptical shaped vortex rope causes anisotropic characteristics of pressure fluctuations around the centerline of the draft tube cone.By analyzing the phase angles of the pressure fluctuations,the role of the vortex rope as an exciter in the oscillating case can be recognized.An analysis of Batchelor instability,i.e.instability in q-vortex like flow structure,has been carried out on the draft tube vortices in these three cases.It can be concluded that the trajectory for study case with part load lies in the region of absolute instability(AI),and it lies in the region of convective instability(CI)for study case with design flow rate.Trajectory for study case with over load lies in the AI region at the inlet of the draft tube,and enters CI region near the end of the elbow.