Toward Efficient Bio-Inspired Propulsion: The Effect of Propulsor Shape and Kinematics on System Performance and Efficiency during Bio-inspired Locomotion

Abstract

Both bird and fish locomotion are thought to be more efficient than the equivalent man-made vehicles driven by propellers/impellers and jet engines. Through studies that decompose the different kinematic and shape effects of these biological systems, we can understand what leads to their high cruising performance and efficiency. Two major studies were conducted. The first was on the effect of different kinematic parameters of large soaring birds on flight performance and the second was on the effect of caudal fin shape on the performance of thunniform swimmers. For the first study on flight performance, flapping, folding, and twist were the wing motions of interest. The second study on swimming performance observed how caudal fin sweep angle affects propulsion while isolating the effect of this shape difference from aspect ratio and area effects. Low order models were primarily used to conduct the bird flight study, though experimental methods were investigated as well. The thunniform swimming study was conducted through experimentation on a biomimetic system. The flight study found that, under the right circumstances, both wing twist and wing folding have a positive effect on flight performance. However, the impact of wing twist is much larger. To incorporate this wing twist into a robotic system, a new reduced order model that partially accounts for 3D effects was developed and validated. In the future, this model can be used in conjunction with a flight controller to control wing twist. The swimming study found that caudal fin sweep had a significant impact on performance, moderately swept fins showing the greatest improvement. Using an overly large sweep angle led to diminished performance when compared to the moderately swept fins, but still demonstrated improved performance over a non-swept fin. The increased performance of the moderately swept fins was due to how it affected LEV formation and stability.