Aerodynamics of 2D unsteady flows dominated by vorticity

M. VALDEZ; S. PREIDIKMAN; J. C. MASSA; B. BALACHANDRAN; D. T. MOOK

Cancun, Mexico

Congreso; PACAM X - TENTH PAN AMERICAN CONGRESS OF APPLIED MECHANICS; 2008

American Academy of Mechanics (AAM)

In this work, some of the aerodynamic mechanisms used by insects and tiny birds arenumerically simulated. These mechanisms are inherently nonlinear and unsteady and, therefore, cannot be captured by a formulation based on linear steady aerodynamic theories. Moreover, an important aspect of this flight is the interaction between the wings and their own wakes; therefore, any realistic simulation must include an accurate model of the wakes. Although the flight of insects and small birds occurs at small chord-based Reynolds numbers, it is still reasonable to assume that viscous effects are restricted to boundary layers on the surfaces of the wings and that vorticity is restricted to those boundary layers and wakes. This hypothesis justifies the use of a modified version of the general unsteady vortex-lattice method (UVLM) that accounts for the possibility of leading-edge separation. The present version of UVLM can also account for time-variations in the camber as well as the chord, and it “splits” vortices and redistributes circulation in the wake in such a way as to keep the spacing nearly uniform, the distribution smooth, and the total circulation constant. Pre-processing, visualization, and post-processing algorithms are developed in order to expedite the comparison of the present numerical results with experimental observations. The characteristics of a well-known flight pattern called “hovering”, in which the insect holds its position in mid-air, is studied. The long-range objective of the present effort is to contribute a numerical tool for predicting the aerodynamic loads associated with the many different flight mechanisms that insects and small birds use. Such a tool can inspire the development of super-maneuverable micro-air-vehicles powered by flapping wings.