The Complicating Effect of Uncertain Flapping Wing Kinematics on Model Validation

Abstract

In order to experimentally validate an aeroelastic modeling tool, a flapping mechanism has been built to flap a flexible wing structure about a single axis. A comparison of the flexible tip deformation during the flapping stroke is of particular interest. Due to the small size of fully-scaled mechanisms, the “commanded” kinematics may differ substantially from what is observed. A crucial input into any numerical flapping wing model, the temporal derivatives of the flapping kinematics, is then not known with certainty. For the current work, the flap rotation is measured with a non-contact image correlation technique, and a Fourier series fit is used to obtain flapping velocities and accelerations. The resulting match between experimental and numerical tip displacements is satisfactory for a very small range of harmonic number. A recommended strategy for future numerical modeling efforts is to include the entire flapping system (power source, actuation, wings) into the framework in order to improve the validation process, with less dependence upon experimental data to “tune” the computational model's input kinematics.