Investigation of the technological deviations influence on the aerodynamic characteristics of unmanned aerial vehicles

Abstract

At the stage of serial production, all the potential of the aircraft must find a practical realization. Such features of the contour such as projecting rivets, surface waviness, steps, cracks, and flashing lights cause the additional drag.Methods for additional drag calculating can be found in various sources, but there is no confirmation how these methods are regular for low Reynolds numbers.The influence of technological deviations on the aerodynamic characteristics of the unmanned aerial vehicle was investigated by the computational fluid dynamics method.The study was performed in Profili 2.27 software, which uses the XFOIL code. It shows a high convergence of calculation results with experimental data for low Mach numbers and a wide range of Reynolds numbers. Each of the airfoils was considered with different positions of the deviation and with its different depth. The calculation was also performed for different Reynolds numbers.Eighteen polars of SD8040 (10%) and HN-417 (10%) airfoils were received. Twelve dependencies of drag coefficient and maximum lift coefficient from the cavity depth, its coordinate and Reynolds number were also presented in the form of tables and graphs. A comparison of the determined impact of surface deviations on aerodynamic characteristics with generalized regularities was made. As a result of the calculation, it was shown that, in general, the cavity shifting backward decreases its effect on the aerodynamic characteristics, since the thickness of the boundary layer increases and the relative cavity depth to this thickness becomes less. Mainly, the Reynolds number decreasing reduces the influence of the cavity on the airfoil aerodynamic characteristics for the same reason. The obtained results meet the known patterns and confirm the correctness of the chosen research method. The impact of the cavity with a 0.5% depth of the chord can significantly reduce the maximal lift coefficient (from 1.28 to 1.21). At the same time, it was found that the effect of deviations from the theoretical contour depends essentially on the particular airfoil shape, even if these airfoils have the same thickness and are geometrically similar. Comparisons with analytical generalizations indicated that the calculated results have one order of value, but unlike theory, they are more complex nonlinear dependences on the cavity depth.Further studies of other airfoils of different thickness and curvature with similar deviations from the theoretical contour are promising as well as using more powerful numerical methods (solving Navier-Stokes equations).