Please cite this article as: M. Dongli, Z. Yanping, Q. Yuhang, L. Guanxiong, Effects of relative thickness on aerodynamic characteristics of airfoil at a low Reynolds number, (2015), doi: http://dx. AbstractThis study focuses on the characteristics of low Reynolds number flow around airfoil of high-altitude unmanned aerial vehicles (HAUAVs) cruising at low speed. Numerical simulation on the flows around several representative airfoils is carried out to investigate the low Reynolds number flow. The water tunnel model tests further validate the accuracy and effectiveness of the numerical method. Then the effects of the relative thickness of airfoil on aerodynamic performance are explored, using the above numerical method, by simulating flows around airfoils of different relative thicknesses (12%, 14%, 16%, 18%), as well as different locations of the maximum relative thickness ( x/c = 22%, 26%, 30%, 34%), at a low Reynolds number of 510 5 . Results show that performance of airfoils at low Reynolds number is mainly affected by the laminar separation bubble. On the premise of good stall characteristics, the value of maximum relative thickness should be as small as possible, and the location of the maximum relative thickness ought to be closer to the trailing edge to obtain fine airfoil performance. The numerical method is feasible for the simulation of low Reynolds number flow. The study can help to provide a basis for the design of low Reynolds number airfoil.

This paper presents the unsteady numerical simulation and analysis of the slipstream generated by distributed propellers on a solar-powered UAV using the CFD method based on structured/unstructured hybrid grids. Sliding mesh technology and a transition model are used for the numerical simulation of a NACA propeller and an Eppler 387 airfoil, the results of which are well compatible with the experimental data, proving the calculation method to be highly credible and accurate. Numerical simulations are run for configurations with the propeller in front of and behind the wing, and comparative analyses are conducted with a pure propeller and pure wing. The results suggest the existence of mutual disturbance between the propeller and the wing, as the propeller, either in front of or behind the wing, causes an increase in cyclical fluctuation of the wing's lift, drag and nose-down moment. The wing, in return, gives rise to an increase in fluctuation of the propeller's pulling force, absorbing power and efficiency, with propeller oscillation being triggered by the discontinuity of the flow field. The configuration with the propeller posed behind the wing is proven to be of smaller disturbance to the whole system.