Experimental study on windage torque in unshrouded rotor-stator system with central inflow

In order to investigate the windage loss on the rotating disc in unshrouded rotor-stator systems, a purpose test rig was applied to measure the frictional torque with static torquemeter as air passed through the rotor-stator system. The unshrouded and the shrouded stationary cases were both investigated with various gap ratio and the flow parameter. The experimental data and an associated correlation for the moment coefficient for the unshrouded case were also presented. The results show that the flow regime, being identified by the turbulent flow parameter plays an important role on friction torque. The flow in the cavity whether is rotational dominant or throughflow dominant will affect the moment coefficient of the rotor. Compared with free disc case, the friction torque of the unshrouded case is mainly affected by the gap ratio. Two critical gap ratios are found with the torque data, the minimum one is G=0.02~0.04 and the maximum one is G=0.06~0.08. For the throughflow dominant case, the moment coefficient of the unshrouded case is about 5 to 15 percent less than the free disc case. The presence of the shroud will enhance the moment coefficient by 20%.