High Advance Ratio Effects on the Aerodynamics and Blade Dynamics of a Slowed Helicopter Rotor

• Applicant: Dr.-Ing. Andre Bauknecht
• Subject Area: Fluid Mechanics
• Term: from 2017 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 383968368

Medical emergency services face the challenge to reach remote locations within a critical response time of less than an hour. Innovative "compound" helicopters with additional propellers, such as Airbus Helicopters' prototype X³, are designed to meet this challenge through a combination of high cruise velocities and vertical take-off capability. To circumvent the impact of high cruise velocities on the advancing blade, the main rotor of a compound helicopter operates at a reduced rotational speed. The corresponding reverse flow on the retreating blade has detrimental effects on the performance and stability of the helicopter. This project focuses on the detailed investigation of the reverse flow field to advance our knowledge of compound helicopter aerodynamics and ultimately design faster helicopters that reduce response times for emergency situations.Experimental evidence shows the impact of reverse flow on the rotor power and loads. To effectively counteract these negative effects, this project will investigate the reverse flow field itself and its subsequent effects on rotor blade deformations. The reverse flow field is characterized by a high advance ratio, the relation of flight speed to blade tip velocity. By manipulating the advance ratio, we can measure its effects on the reverse flow field and blade deformations of a slowed rotor. These measurements, in turn, will improve the aerodynamic rotor codes used in the conceptual design of compound helicopter configurations, which are currently insufficient for accurate prediction of the complex flow physics in the reverse flow field. The proposed project will be carried out in cooperation with the Alfred Gessow Rotorcraft Center and Jones Aerodynamics Laboratory at the University of Maryland. A four-bladed, slowed model rotor will be tested at high advance ratio in the Glenn L. Martin Wind Tunnel. The reverse flow field and deformations of the retreating blade will be measured simultaneously by time-resolved stereo particle image velocimetry and stereo photogrammetry, respectively. The combination of state-of-the-art facilities, a fully funded wind tunnel test, and researcher expertise in this project is essential to investigate reverse flow on a slowed rotor and improve the design of future compound helicopters.

• DFG Programme: Research Fellowships
• International Connection: USA
• Hosts: Professor Dr. Inderjit Chopra; Professorin Dr. Anya Jones