Abstract
Unavoidable tip clearance between blade tip and casing shroud plays an important role in the performance and characteristics of a tidal propeller turbine. In this work, the tip-leakage vortex (TLV) induced in the end-wall region was numerically illustrated by using the shear-stress transport (SST) k–ω turbulence model at various flow conditions and different tip-clearance sizes (TCSs). The swirling strength criterion was employed to visualize the tip-leakage vortex trajectory and investigate vortex evolution according to clearance size change. Although TLV occurs in both design and off-design conditions, vortex intensity develops strongly under excess flow rate with increased tip gap. The extreme influence of TCS on the turbine’s generated power and efficiency was predicted in steady simulations for four TCS cases, namely, δ = 0%, 0.25%, 0.5%, and 0.75%. With the extension of the tip gap, turbine performance was drastically reduced because of vigorous turbulent leakage flow combined with considerable volumetric loss. The effect of TCS on pressure fluctuation intensity were also explored on the basis of the transient simulation statistic. Maximal pressure variation amplitude and dominant frequency were presented in spectrum analysis utilizing fast Fourier transform.
Highlights
Among the several types of renewable energy, hydropower is one of the most commonly used sources with a vast amount of power scale and applications since it is emission free, clean, and friendly to the environment
Samora et al were used to η/η1method [26]
0.999472 validate our numerical propeller turbine designed on the basis of free-vortex theory and a constant-thickness-blade prototype was made to perform the experiment at different rotational speeds andVerification flow conditions to characterize its performance curves
Summary
Among the several types of renewable energy, hydropower is one of the most commonly used sources with a vast amount of power scale and applications since it is emission free, clean, and friendly to the environment. Hydro-turbines converting flow kinetic energy to electricity have been developed and are widely employed in both civil and industrial fields. An important factor affecting flow characteristics and turbine efficiency is the blade tip clearance. The flow through the tip clearance is called tip-leakage flow generated by the difference in pressure between two sides (pressure side and suction side) of the turbine blade [1]. Tip-leakage vortex (TLV) detrimentally impacts machine performance, such as via blockage of the main flow in the passages [2], reduction of energy extraction ability and efficiency [3], and excessive noise [4] due to the existence of separation flow, volumetric loss, and cavitation
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