The influence of runner cone perforation on the draft tube vortex in Francis hydro-turbine

Influencia de la perforación del cono del rodete en el vórtice del tubo de aspiración de una turbina hidráulica Francis

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ID: 89759
2018
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Abstract
In Francis hydro-turbine, the pressure oscillation in the draft tube is the main source of flow-induced vibration and noise. The structural design of runner cone exerts significant influence on the tangential flow velocity within the draft tube and the pressure fluctuations downstream. In this work, we propose a simple and effective method by perforating through-holes on the runner cone to weaken or eliminate pressure fluctuations induced by the vortex ropes in draft tube. An 2 and 4 holes are perforated on the lower half of runner cone, and numerical simulations and experiments are conducted to understand the changing of phenomenology and features with regard to vortex ropes and pressure levels, comparing with the original unperforated case. The analyses are done for two different guide vane openings, α, and the results were validated by experiments with high-speed photography. It is found that at the two openings, the runner cone with perforations can reduce the volume of vortex ropes, and decrease the pressure fluctuation level. The motion of vortex ropes tends to be less violent with more perforated holes. Therefore, the runner cone perforation has the potential of reducing the vortex rope strength.
En las turbinas hidráulicas Francis, la oscilación de presión en el tubo de aspiración constituye la principal fuente de ruido y vibraciones inducidos por el flujo. El diseño estructural del cono del rodete ejerce una influencia significativa sobre la velocidad tangencial del flujo en el interior del tubo de aspiración y sobre las fluctuaciones de presión aguas abajo. En este trabajo, se propone un método sencillo y eficaz consistente en realizar orificios pasantes en el cono del rodete para atenuar o eliminar las fluctuaciones de presión inducidas por las antorchas de vórtice en el tubo de aspiración. Se perforan 2 y 4 orificios en la mitad inferior del cono del rodete, y se llevan a cabo simulaciones numéricas y ensayos experimentales para comprender la variación de la fenomenología y de las características relativas a las antorchas de vórtice y a los niveles de presión, en comparación con el caso original sin perforaciones. Los análisis se realizan para dos aperturas diferentes de los álabes directrices, α, y los resultados se validaron experimentalmente mediante fotografía de alta velocidad. Se constata que, en ambas aperturas, el cono del rodete con perforaciones logra reducir el volumen de las antorchas de vórtice y disminuir el nivel de fluctuación de presión. El movimiento de las antorchas de vórtice tiende a ser menos violento a medida que aumenta el número de orificios perforados. Por consiguiente, la perforación del cono del rodete presenta el potencial de reducir la intensidad de la antorcha de vórtice.
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Journal thermal science
Year 2018
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