A. GEERAERT, C. STEPHAN
DOI Number: N/A
Conference number: IFASD-2015-023
Although contra-rotating open rotors (CROR) were experimented mainly in the 40’s, even limitedly produced in some countries, and with enhanced performances compared to single propellers, their complex design, installation and maintenance prevented them from being used over an extended period of time. The current research by aeronautical community on bringing significant step changes regarding the environmental impact of aviation has given new impetus to this kind of propulsion system. Within the CleanSky SFWA-ITD project, recent wind tunnel tests campaigns have been performed to get a deeper understanding of the complex phenomena involving aerodynamic, acoustic, structural, performances, and aeroelastic topics. Concerning particularly the latter topic, this European project has been an opportunity to improve both experimental and numerical methods to estimate operational blade deformation. The whole achieved work is described in two companion papers. This first paper presents the preparation and application of the Strain Pattern Analysis (SPA) during the Z49 CROR wind tunnel tests, with Airbus AI-PX7 generic blades [1], as the experimental method used to determine the steady and unsteady blade deformations over all azimuths by recombination of reduced number of modal shapes. The important initial step of optimising the strain gauges bridges locations by maximising the structural modes observability and minimising the information redundancy shared by a set of sensors is detailed. Instrumentation constraints taken into account are listed to highlight the difficulty of applying the SPA with such composite structures. Then a numerical sensitivity study, from which results are exposed, has been performed before manufacturing the blades to determine the optimal set of SPA parameters and to evaluate the expected error induced by SPA on a reference case in cruise conditions. The next phase concerning the laboratory tests results is detailed, describing the calibration of the instrumented blades, the instrumentation verification in non-rotating and rotating conditions, as well as a first validation of the SPA of blades subject to a distributed static loading. The final experimental step concerns the application of SPA during the wind tunnel tests (WTT) at ONERA S1MA facility, from signal preprocessing to typical final results, such as steady and unsteady bending and twist, useful for a better understanding of the blades aeroelastic behaviour and CROR performances. A companion paper [7] describes the improvement of numerical methods to calculate the blades aeroelastic deformation and compares the obtained numerical results with experimental SPA results mentioned here-above.