Towards an optimum pitch to chord ratio and establishing its scaling effects in low head Kaplan propellers.

Notwithstanding the long historic journey of Kaplan turbines for hydropower generation, the inner design details like position of guide vane relative to runner, blade pitch to chord ratio amongst others are yet to be investigated in depth let alone being standardized. This dearth widens in small capacity hydropower plants. The current study chooses the blade pitch to chord as research theme to be investigated both experimentally and numerically on a medium-high specific speed Kaplan turbine. Three levels of study are envisaged for obtaining the optimum ratio. The first is the change of blade number with chord fixed, the second is fixing the blade number and changing the chord length and final level of keeping the ratio constant by varying the pitch and chord by identical proportion attempts to clarify the scaling effects. Optimum efficiency in the range of 78%–82% for ratios 1.2 to 2.2 are observed for smaller pitch, smaller chord condition. The scaling study at optimum ratio revealed that increasing the blade pitch distance causes the exit fluid deflection deteriorating the performance. The paper strongly recommends a wider pitch-chord ratio study in higher specific speed Kaplans to get standardized scaling effects with respect to size and achieve universality. • Kaplan turbine with 4 blades,D = 218 mm,1570 rpm,pitch(t)/chord(t) at tip = 1.6 chosen. • 9 cases investigated with blade number 2, 3 and 4; chord length ratio 0.5, 0.75, 1.0 • Efficiency increased by 15% as t/l decreased from 3.2 to 1.6, at fixed chord 'l'. • Small pitch and small chords improved performance by 2–8% at given t/l. • Novel study of scaling effect done on inter-blade space and fluid deflection. [ABSTRACT FROM AUTHOR]