Abstract: To make full use of the energy of reciprocating flow in the oscillating water column, this study numerically simulates and analyzes the performance of an impulse turbine in the conditions of steady air flows and reciprocating air flows, including analysis of the input coefficient, torque coefficient and efficiency. Accuracy of the numerical calculations is verified through comparison to previous studies in the literature. The results show that as important geometric parameters of the impulse turbine, the outer diameter clearance should be about 1 mm and the number of moving blades be 30. In reciprocating flow modes, the performance curve of an impulse turbine has a hysteresis loop due to its different performances in acceleration and deceleration stages. And because of different pressure drops in these two stages, the input coefficient curve has a clockwise hysteresis loop, while the efficiency curve has an anticlockwise hysteresis loop. In contrast, the torque coefficient shows no obvious hysteretic behavior. Comparison of the results of steady and reciprocating flows reveals the lower reciprocating flow frequency results in the turbine performance closer to that of the steady flow case.

Key words: impulse turbine, numerical simulation, steady flow, reciprocating flow, hysteresis, quasi-steady analysis