Impact of solidity and speed ratio on the performance of a contra-rotating fan

In this study, the effects of solidity and rotor speed ratio on the performance of a contra-rotating fan are investigated numerically. Simulation results have been validated by experimental tests. The test stand construction and the measurements have been performed according to ISO-5801 standard. In order to investigate the effect of blade solidity, simulations have been conducted with constant blade count of the front rotor and four configurations of the rear rotor (having 6, 8, 12 and 16 blades), and also constant blade count of the rear rotor and three configurations of the front rotor (having 8, 12, and 16 blades). Results suggest that there is an optimum solidity for the rear rotor, which gives maximum pressure rise and efficiency. Furthermore, the effects of the rotor speed ratios have been investigated in this study. It is shown that the speed of the front rotor is more effective on the fan performance, as compared to the rear rotor. Results reveal that the performance drop caused by a 25% reduction in the rear rotor blade count, can be compensated by 5% increase of the front rotor rotational speed. Therefore, a suitable choice of the speed ratio can result in light-weight and high-performance contra-rotating stages.