Application Of The VLM To The PropulsivePerformance Of A Pair Of Oscillating Wing-tails

Abstract

A 3-D unsteady vortex lattice technique is applied to the analysis of a pair of vertical oscillating wing tails, in order to investigate quantitatively its propulsive performance. Each lifting component undergoes a combined transverse and angular motion at the same frequency, in a uniform inflow condition A freewake analysis is incorporated in order to account for the effects of non-linearity, especially at increased amplitudes of oscillatory motion Wing thickness effects are taken into account by an appropriate linearisation of the no-entrance boundary condition, and the effects of viscosity by means of a factional drag coefficient applied to the solid surface. Numerical results are presented vs. experimental measurements for the propulsion thrust coefficient and the efficiency of the system over a range of motion parameters, including wing's aspect ratio, Strouhal number, feathering parameter and phase lag between oscillatory motions. These results indicate the significance of 3-D effects and show that the present technique, after appropriate elaboration, especially as concerns unsteady LE flow separation and stall effects, can serve for the design of this kind of propulsive systems with optimised performance.