Abstract
The Kaplan turbine is an axial propeller-type turbine that can simultaneously control guide vanes and runner blades, thus allowing its application in a wide range of operations. Here, turbine tip clearance plays a crucial role in turbine design and operation as high tip clearance flow can lead to a change in the flow pattern, resulting in a loss of efficiency and finally the breakdown of hydro turbines. This research investigates tip clearance flow characteristics and undertakes a transient fast Fourier transform (FFT) analysis of a Kaplan turbine. In this study, the computational fluid dynamics method was used to investigate the Kaplan turbine performance with tip clearance gaps at different operating conditions. Numerical performance was verified with experimental results. In particular, a parametric study was carried out including the different geometrical parameters such as tip clearance between stationary and rotating chambers. In addition, an FFT analysis was performed by monitoring dynamic pressure fluctuation on the rotor. Here, increases in tip clearance were shown to occur with decreases in efficiency owing to unsteady flow. With this study’s focus on analyzing the flow of the tip clearance and its effect on turbine performance as well as hydraulic efficiency, it aims to improve the understanding on the flow field in a Kaplan turbine.
Highlights
Kaplan hydroturbines are widely used in hydropower plants because of their high efficiency over a wide range of operating conditions
Gehrer et al [14] examined the cavitation caused by the tip clearance of a Kaplan turbine by simulation in the runner blade optimization based on an evolutionary algorithm, and Bodkhe [15] studied the experimental analysis of Kaplan turbines at different operating load conditions
Numerical analysis of the fluid flow was based on the continuity and momentum equations [25,35], which are expressed as Equations (3) and (4) as follows, respectively:
Summary
Kaplan hydroturbines are widely used in hydropower plants because of their high efficiency over a wide range of operating conditions. Gehrer et al [14] examined the cavitation caused by the tip clearance of a Kaplan turbine by simulation in the runner blade optimization based on an evolutionary algorithm, and Bodkhe [15] studied the experimental analysis of Kaplan turbines at different operating load conditions. To extract the characteristics of fluctuated signals, mathematical tools like the fast Fourier transformation (FFT) analysis is often utilized, wherein the signals’ features in the time domain, frequency domain, or amplitude can be obtained Such methods are significantly helpful for the working stability and state inspection of hydroturbines [27,28]. Unsteady three-dimensional turbulent flow throughout the full domain of a Kaplan turbine was investigated through simulations, and the pressure pulsation in the runner and generator (hub) was predicted and analyzed using the FFT analysis
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