A bidirectional axial-flow impulse turbine installed in an oscillating water column raises the question of damping at different wave conditions. This article reports unsteady performances of such a turbine in an airflow test rig. The rig has a piston-cylinder arrangement, and the piston, when reciprocating, generates the oscillatory airflow. At a very low wave height (piston stroke length, <0.4 m), the turbine speed is very low. Time series analysis of pressure drop and speed are reported for higher stroke lengths, which shows the rate of increase and decrease in velocity of the turbine. Furthermore, the turbine pressure coefficient and the damping characteristics of the test rig chamber were estimated. Finally, the chamber damping verifies that the turbine-chamber coupling effect is reciprocal.