Design of an active compressor blade for aeroelastic studies

This thesis begins the development of a tool that will enable direct measurement of the unsteady aerodynamic response of a transonic compressor for use in flutter identification. The experimental apparatus, named the Active Rotor, will have active blades with individual motion control. The Active Rotor Blades, proposed in this work, uses a spar-and-shell concept which consists of a flexible outer foam shell, structural spars, and piezoelectric actuators. The graphite epoxy spars both carry the load of the blade and induce shape changes of the blade from attached piezoelectric actuators. Control of a blade shape and position to the airflow allows new experiments to be performed in the area of flutter and unsteady aerodynamics. A design study was performed to choose several of the material and geometrical properties of the Active Rotor Blade. A NASTRAN/PATRAN finite element model was developed with these design parameters to calculate the stresses in the composite spars, the level of tip rotation available from piezoelectric actuation, and the strains seen by the piezoceramic under full centrifugal loads. The spar stresses and available actuation were within required ranges, but the strain predictions on the piezoceramics were near the ultimate. The composite spar modeling and piezoelectric actuation modeling were verified with experimental results. The piezoceramics were protected from large tensile strains by bonding to the composite with a compressive prestrain. Experiments on the bond layer characterized its strength and ability to hold the desired precompression. Testing identified piezoelectric actuation under loads specific to the Active Rotor Blade: compression, release of compression, and tension. The piezoceramics were bonded to different composite layups with different Poisson's ratios to assess the effect of biaxial stress states. Results indicate that the biaxial stresses have a larger influence on actuation than the precompression. The piezoceramic was not observed to lose structural integrity or show a large loss in actuation when pulled significantly beyond its failure strain. The increased strength is attributed to the packaging designed for the Active Rotor. Thesis Supervisor: Professor Carlos E. S. Cesnik Title: Assistant Professor of Aeronautics and Astronautics Acknowledgments I would like to thank my advisor, Professor Carlos Cesnik, for allowing me a great amount of freedom in this project. Through his in-depth discussions and through his excellent teaching ability, he kept my work as a graduate student interesting and rewarding. I am thankful for his support. Thanks to Professor Jim Paduano for being patient with the continual structural and material problems that arose at every turn. And to Professor Paul Lagace whose overdeveloped sense of competition can't always match that of a student. Forget arm wrestling. softball, anyone? Many thanks to the undergraduate research assistants that worked with me on this project. Andy Oury, who had the independence and motivation to work out several of the manufacturing details, and who was invaluable for getting the test equipment in a usable fashion. Anna Park, whom, despite the horrors of the machine shop, was always smiling and producing very nicely tapered composite spars. Mike Kim, who kept the assembly line of packaging piezoceramics running smoothly, and Paul Goulart and Matt Lockhart for their contributions. I would like to thank John Kane, the TELAC lab technician, whose experience and humor was well appreciated, and John Rodgers, whose work on Active Fiber Composites kept me continually seeking his advice and borrowing from his supplies. And many thanks to Debashis Sahoo, who worked with me on the finite element modeling, and whom I am sure will do fantastic work in continuing the project. I must thank those members of GTL and TELAC and that whole group of Draper Fellows (who somehow all found it convenient to graduate on time), that kept life a GFT. I make a special thanks to my family for making all of this possible. Funding for this research was provided under the Air Force Office of Scientific Research (AFOSR) Grant Number F49620-95-1-0280, and Grant Number F49620-95-1-0409: their support is gratefully acknowledged.