Brown’s Vorticity Transport Model has been used to predict the wake structure and resultant
blade loading of the rotor that was studied during the HART II experimental programme.
The descending flight condition of the experiment yields significant high-frequency content to
the blade loading due to the presence of blade-vortex interactions. PIV images of the wake
structure were compared against numerical predictions of the detailed geometry of the rotor
wake using three different computational resolutions of the flow. This was done to investigate
the origin of inaccuracies exposed in an earlier study of the system in capturing the effects of
blade vortex interactions on the loading on the rotor. The predicted positions of the vortex
cores agree with measured data to within a fraction of the blade chord, and the strength of the
vortices is preserved to well downstream of the rotor, essentially independently of the resolution
of the calculation. Nevertheless the amplitude of the loading impulses induced on the blade by
vortex interaction are strongly influenced by the resolution of the calculation through the effect
of cell density on the minimum vortex core size that can be supported. It would appear thus
that the inaccuracies in predicting the high-frequency loading on the rotor are not due to any
inherent deficiency in the representation of the wake, although viscous effects may need to be
considered in future in order to decouple the vortex core size from the cell size, but rather due
to the inherent deficiencies of the lifting line approach used to model the blade aerodynamics