A Feasibility Study To Control Airfoil Shape Using THUNDER

The use of trademarks or names of manufacturers in this report is for accurate reporting and does not constitute an official endorsement, either expressed or implied, of such products or manufacturers by the National Aeronautics and Space Administration. Summary The objective of this study was to assess the capabilities of a new piezoelectric actuator to alter the upper surface geometry of a subscale airfoil to enhance performance. This new piezoelectric actuator called thin-layer composite-unimorph ferroelectric driver and sensor (THUNDER), recently developed at Langley Research Center, is manufactured to deform out of plane when under an applied voltage and, to date, has exhibited much larger displacements than other piezoelectric actuators. It was anticipated that attaching a THUNDER wafer to the upper surface of a small airfoil and actuating it to increase the camber of that surface when the airfoil was at positive angles of attack (above 2°) would extend the region of attached flow across the upper surface. Two common characteristics of all piezoelectric actuators, creep and hysteresis, however, pose challenges when THUNDER is used for airfoil shaping or other positioning applications. For this study, a subscale airfoil model was designed, fabricated, and tested under two-dimensional flow conditions in a small tabletop wind tunnel. Sixty test conditions, consisting of combinations of five angles of attack, four direct current (dc) applied voltages, and three tunnel velocities, were studied. Results indicated that displacements of the upper surface of the airfoil were affected by the magnitude of the applied voltage, the tunnel velocity, the airfoil angle of attack, and the creep and hysteresis of the THUNDER wafer. Larger magnitudes of applied voltage produced larger wafer displacements. Wind-off wafer displacements were consistently larger than corresponding wind-on displacements; however, higher velocities produced larger displacements than lower velocities because of increased upper surface suction. Larger displacements were also recorded at higher angles of attack because of increased upper surface suction. Creep and hysteresis of the wafer were identified at each test condition and contributed to larger negative displacements for all negative applied-voltage conditions and larger positive displacements for the smaller, positive applied-voltage (+102 V) condition. An elastic membrane used to hold the wafer onto the upper surface hindered displacements at the larger magnitude positive applied voltage (+170 V). Both creep and hysteresis of the THUNDER wafer appeared bounded, based on the analysis of several displacement cycles. These results show that THUNDER can be used to alter the …