Outwash Test Results for a Single Rotor in Hover (Presentation Only)

Abstract:
In September 2025 a test was conducted at the NASA Ames Research Center's Outdoor Aerodynamics Research Facility to characterize the outwash flow from a hovering rotor. The studied configurations included variations in rotor height above the ground plane as well as variations in rotor speed, thrust, and trim state. Outwash flow was measured using a rake of hot-film anemometers mounted to a semi-autonomous instrumentation cart. Flow measurements were conducted for a single rotor azimuth at distances between 0.6 and 4.0 diameters from the rotor center. In addition to hot-film anemometry, additional flow data was captured using a Background Oriented Schlieren Velocimetry technique that provides a detailed measurement over time of flow velocity in an image plane upstream of the hot-film sensors. The downwash and outwash produced by a lifting rotor in the presence of a ground plane can pose significant risks to life and property in the area of operations. Rotor wake interactions exhibited by modern, multi-rotor aircraft designs can amplify these flows and increase the risk. The rotorcraft community is therefore motivated to better understand rotor downwash and outwash to establish safe operating limits in the vertiport environment.

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