Low Reynolds Number Scaling Effects For Small-Scale Rotors

Three T-Motor rotors with different diameters but otherwise identical relative geometries were tested in fully edgewise flow at different advance ratios and Reynolds numbers. The objective was to verify whether the existing scaling relationships between rotor size and the aerodynamic forces are applicable to small scale rotors that operate at relatively low chord-Reynolds numbers. The rotors were mounted onto a test stand housed inside a closed loop wind-tunnel where the air speed of the tunnel was varied to achieve different advance ratios. The chord-Reynolds umber at 75% of the radius of each blade were matched for ranges from 39,000 to 117,000. The experimental data was also compared to computational results from a blade element momentum theory-based method. The results showed that the existing coefficient based scaling laws can be used to predict the performance parameters for the thrust coefficient, power coefficient, longitudinal force coefficient, side force coefficient and, rolling moment coefficient for the full range of Reynolds numbers tested. Although for the pitching moment coefficient, a coefficient approach became less applicable for chord-Reynolds number of less than 100,000.