Water Tunnel Flow Diagnostics of Wake Structures Downstream of a Model Helicopter Rotor Hub

摘要

A scaled model of a notional helicopter rotor hub of a large helicopter was tested at Reynolds numbers of 2.45×10~6 and 4.90×10~6 based on the hub diameter at an advance ratio of 0.2 in the 48-inch 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 downstream locations. Blind computations of the rotor hub flow were also performed by Sikorsky Aircraft and compared with the experimental results. Various flow structures were identified and linked to geometric features of the hub model. The most prominent structures were 2/revolution (scissors) and 4/revolution (main hub arms) vortices shed by the hub. Both the 2/revolution and 4/revolution structures persisted far downstream of the hub, but the rate of dissipation was greater for the 4/rev structures. A 6/rev structure was also observed, which is conjectured to be the result of Strouhal shedding. This work provides a data set for enhanced understanding of the fundamental physics underlying rotor hub flows and serves as validation data for future computational analyses.