In-Flight PIV for CROR Flight Test Demonstration

Designing innovative solutions for future aircraft is one the concerns of aeronautical engineers. Among the studied technologies, Counter Rotating Open Rotor (CROR) propeller technologies are appearing as a promising, though highly challenging, alternative solution to Ultra High Bypass Ratio (UHBR) engines. Amongst these challenges, the interaction of the wake of the CROR engine pylon with the counter rotating blades, positioned downstream of the pylon (pusher configuration), are responsible for both airframe noise and vibrations that penalize aircraft certification. ‘Erasing’ the pylon wake such as to recover a strictly uniform flow upstream of the rotating blades would suppress this major source of airframe noise and vibrations. The current study is put forward in that context and is part of a project funded by the European Commission through the Cleansky/FP7/SFWA (Smart Fixed Wing Aircraft) Demonstrator program. In the first part of the project, an optimal design of the pylon, associated with advanced flow control strategies, has been proposed. The current study aims at developing an advanced experimental methodology, based on vibration-controlled stereoscopic Particle Image Velocimetry (3C-PIV), able to be flight-operated and that will serve the validation of the above mentioned active flow control system when operated on the Flying Test Bench. This article deals particularly with the characterization of the limits of the vibration spectrum acceptable by the on-board PIV subsystems and with the design of a system to lessen potentially harmful vibrations