Reynolds number dependence of coaxial rotor wakes in climb and hover
Pennsylvania State University
Abstract
Coaxial rotor configurations are becoming more commonplace on specific aerospace applications, such as electric vertical take-off and landing rotorcraft. However, from a fundamental perspective, coaxial rotors have not been studied as extensively as single main rotors meaning that less is known about their underlying fluid dynamics. In this work, the Reynolds number (or scale) dependence of the coaxial rotor wake in axial flight is examined using a specialized, high pressure wind tunnel known as the Penn State Compressed Air Wind Tunnel (CAWT). In this facility, flight-relevant Reynolds numbers can be achieved using relatively small models. Wake surveys were conducted on a coaxial rotor system based on the NASA Dragonfly geometry at several downstream locations to determine the Reynolds number sensitivity for both mean and fluctuating axial velocities. Results indicate that only moderate Reynolds numbers are required before invariance in Re is achieved. Spectra calculated from the axial fluctuating velocity show evidence of wake meandering for rotors in hover. These findings offer the first detailed look into coaxial rotor configuration wake scaling by quantifying how downstream wake dynamics are affected by the flight condition.
About the speaker
Dr. Mark A. Miller’s research at Penn State focusses on the fundamental fluid dynamics of unsteady and rotating systems by using a multifaceted experimental and theoretical approach. Ongoing projects span a wide range of fluid systems including multi-rotor electric Vertical Take-Off and Landing (eVTOL) performance and acoustic characterization, wind turbine aerodynamics, turbulent flows and roughness, as well as the development of innovative sensor systems which are tailored to these specific flow regimes. He is an active member of the American Physical Society, the American Society of Engineering Education, the AIAA, where he serves on the Fluid Dynamics Technical Committee, and the Vertical Flight Society, where he serves on the Test and Evaluation Committee.
