Measurement and Prediction of Model-Rotor Flowfields

A laser velocimeter was used to measure accurately the three-component velocities induced by a model rotor at transonic tip speeds. The measurements, which were made at Mach numbers 0.85-0.95 and at zero advance ratio, yielded high-resolution, orthogonal velocity values. The measured velocities were used to check the ability of the ROT22 full-potential rotor code to predict the transonic flowfield in the crucial region around and beyond the tip of a high-speed rotor blade. The good agreement between the calculated and measured velocities established the code's ability to predict the off-blade flowfield at transonic tip speeds. This supplements previous comparisons in which surface pressures were shown to be well predicted on two different tips at advance ratios of 0.40 and 0.45, especially at the critical 90-deg azimuthal blade position. These results demonstrate that the ROT22 code can be used to predict the important tip-region flowfield, including the occurrence, strength, and location of shock waves causing high drag and noise.