Analysis of Bulb Turbine Hydrofoil Cavitation

Andrej Podnar,Matevž Dular,Lovrenc Novak,Marko Hočevar

doi:10.3390/app11062639

Abstract

The influence of a bulb runner blade hydrofoil shape on flow characteristics around the blade was studied. Experimental work was performed on a bulb turbine measuring station and a single hydrofoil in a cavitating tunnel. In the cavitation tunnel, flow visualization was performed on the hydrofoil’s suction side. Cavitation structures were observed for several cavitation numbers. Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number. The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures. A regression model was produced for cavitation cloud length. The results of the regression model show that cavitation length is dependent on Reynolds’s number and the cavitation number. The coefficients of determination for both the existing and modified hydrofoils were reasonably high, with R2 values above 0.95. The results of the cavitation length regression model also confirm that the modified hydrofoil exhibits improved the cavitation properties.

Highlights

Hydropower was used as a source of baseload generation for electric power, but it is increasingly used for grid balancing
Cavitation was less intense on the modified hydrofoil than on the original hydrofoil, delaying the cavitation onset by several tenths in cavitation number
The results of the visualization in the cavitation tunnel show that modifying the existing hydrofoil design parameters played a key role in reducing the cavitation inception and development, as well as the size of the cavitation structures

Summary

Introduction

Hydropower was used as a source of baseload generation for electric power, but it is increasingly used for grid balancing. Among dispatchable renewable energy sources, hydropower plants are the most often used [1], achieving up to 15 s response times [2] for 90% of the total power response. Including nondispatchable renewable energy sources, e.g., inter alia wind and photovoltaics, and market deregulation, creates the requirement for rapid power generation fluctuations and power increase in the afternoon [3,4,5]. Any new hydraulic turbine design should enable this type of operation and reach high efficiency and stable operation outside its optimal operating interval. Besides stable continuous turbine operation away from the best efficiency point, new designs will need to function sufficiently in transient operation. Bulb turbines face challenges for such operation; designers will have to overcome the detrimental effects that flow fluctuations and cavitation have on turbine operation, while still ensuring adequate performance over a broad interval of operating points and in transient operation [3]

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Results

Conclusion