Effects of Reynolds Number and Advance Ratio on the Drag of a Model Helicopter Rotor Hub

A 1:17 scale model of a notional rotor hub of a large helicopter was tested in the Pennsylvania State University (PSU) Applied Research Laboratory (ARL) 12-inch test section water tunnel. Objectives of the experiment were to quantify effects of Reynolds number, advance ratio, and hub geometry configuration on the drag and shed wake of the rotor hub. A range of flow conditions were tested, with hub diameter-based Reynolds numbers ranging from 1.06×10⁵ to 2.62×10⁶ and advance ratios ranging from 0.2 to 0.4, as well as non-rotating cases. Three hub geometry configurations were tested with various combinations of components including fairing, blade stubs, spiders, scissors, swashplate, and pitch links. Primary measurements were steady and unsteady hub drag and Particle Image Velocimetry at two downstream locations. Results include time-averaged, phase-averaged, spectral analysis of the unsteady drag, and wake velocity. A strong dependence of steady and unsteady drag on Reynolds number and advance ratio was noted, eluding to the importance of adequate Reynolds scaling for model helicopter rotor hub tests.