Windage measurements for rotating disc with protrusions

A new test rig was performed to investigate the windage torque of the rotating disc with protrusions or roughness on the rotor surface. The new measurement method was verified accurately with the comparison between the free disc data and the correction in open literatures. Six configurations of protrusion were carried out. The results show that the moment coefficient of rotor increases with increasing the disc surface roughness. The increasing roughness from hydrodynamically smooth to a roughness ratio of 1120 (corresponding to a roughness height of 0.2 mm) causes a double torque value of rotor within the test range. The impact factors obtained from hydrodynamically smooth disc case were derived for the roughness disc cases. The blade shape protrusion caused the smallest friction torque of the rotor within the six configurations. Changing the protrusions orientation with respect to the direction of the fluid causes the moment coefficient a difference of approximately 10 percents. New correlations were proposed for the windage torque for the hydrodynamically smooth and the roughness rotor cases and the rotor with protrusions respectively.