First rotor hub flow prediction workshop experimental data campaigns and computational analyses

The rotor hub can account for up to thirty percent of rotorcraft parasite drag. Therefore, reducing hub drag is mandatory to advance the scientific knowledge necessary for future high-speed conventional and compound rotorcraft. The importance of high-Reynolds number testing of rotor hub flows is paramount as turbulent coherent structures persist up to the long-age wake where they interact with the empennage and tail, an observation impossible to make in experiments at lower Reynolds scale due to viscous dissipation. Basic Vertical Lift Center of Excellence (VLRCOE) research at Penn State in water tunnel facilities has provided unique high Reynolds-scale data of rotor hub wakes, providing new data for physical understanding and validation of computational fluid dynamics (CFD) methods. A first rotor hub flow prediction workshop is the result of a collaboration between Penn State and Georgia Tech VLRCOEs with support from the National Rotorcraft Technology Center (NRTC), including participation from academia, industry, and government. This paper describes the experimental data campaigns on hub flows conducted in the Penn State water tunnels and used for CFD comparisons/validations at the workshop. The 'First Rotor Hub Flow Prediction Workshop' is a compelling example of productive exchange between experimental and computational efforts, resulting in suggestions for post-workshop experiments and CFD analyses, some of which are highlighted in this paper.