Development and Application of a CFD-based Engineering Analysis of Hover Performance

The vorticity embedding method for the prediction of rotor hover performance, as implemented in the Helix-Ia code, is shown to be suitable for use as a routine engineering tool — it is probably the first CFD hover analysis to attain this capability. This is the result of improvements to the wake representation and increased code speed. Two landmark experiments are the basis for validation computations shown herein. Comparison with the model UH-60A data of Lorber et al. shows that the method predicts hover performance, wake configuration and blade loads; that is, it accurately predicts performance and the measured bases for that performance. The second experiment used for validation is the multi-blade-number test of Knight and Hefner (K-H), which shows the ability to predict a wide number of different rotor configurations. The little-known K-H work also includes a blade-element-momentum analysis in which a useful set of similarity scaling variables was discovered. Not only do the present computations agree well with the K-H data, but K-H scaling permits the comparisons (for four rotors of different blade number) to be contained within two curves, one for scaled thrust coefficient and one for a modified/scaled torque coefficient. The generality of the K-H scaling (explored herein using the Helix-Ia code) is remarkable and such scaling (or a variant thereof) is recommended for future presentations of hover performance results.