A scaled model of a notional helicopter rotor hub was tested at hub-diameter-based Reynolds numbers of 2.45 million and 4.9 million based on the hub of a large helicopter at an advance ratio of 0.2 in the 48" Garfield Thomas Water Tunnel. The main objectives of the experiment were to understand the spatial and temporal content of the unsteady wake downstream of a rotor hub up to a distance corresponding to the empennage. Primary measurements were the total hub drag and velocity measurements at three nominal downstream locations. Various flow structures were identified and linked to geometric features of the hub model. The most prominent structures were two-per-revolution (scissors) and four-per-revolution (main hub arms) vortices shed by the hub. Both the two-per-revolution and four-per-revolution structures persisted far downstream of the hub, but the rate of dissipation was greater for the four-per-revolution structures. A six-per-rev structure was also observed, which is conjectured to be from Strouhal shedding. This work provides a dataset for enhanced understanding of the fundamental physics underlying rotor hub flows and serves as validation data for future CFD analyses.
