Experimental study of passive flow separation control by backward facing step with different aspect ratios of Naca 0012 wing

Abstract

The lifting surface may be considered as a tool which develops a useful reaction force during its motion relative to the fluid. The surfaces of wings and tails of airplanes, propellers and blades of turbo-machinery are some of the examples of the lifting surfaces. The production of the maximum possible lift force and that of the minimum possible drag force in directions perpendicular to the direction of motion depends on the optimum design of lifting surface. Aspect ratio is an important technique for the improvement of aerodynamic characteristics through drag reduction. In that present work, the effect of aspect ratio on the airfoil characteristic of NACA 0012 wing is investigated through experiments as a function of angle of attack and also the passive flow separation is controlled by introducing backward facing step to the optimum airfoil. The ability to manipulate a flow passively or actively is of immense technological importance. An interference drag between wing and body also plays an important role on the performance. The magnitudes of aerodynamic forces on airfoils resulting from the incompressible viscous flow fields are determined experimentally. Three wing models of different aspect ratios such as AR=2, AR=1 and AR=0.5 of symmetrical airfoils type NACA 0012, are tested in this experiment, with different angle of attack ranging from 0° to 20° keeping the surface area alike. The aerodynamic characteristics such as coefficient of lift, coefficient of drag and coefficient of lift to drag ratio and coefficient of performance for different models is determined from the static pressure distribution.

After analyzing the data, it is found that the pressure differences between the upper and lower surfaces are higher for wing model of AR 2 than other two models of AR 0.5 and AR 1.It is observed that the critical angle of attack of all the wing models remain around 120 beyond which stall occurs but for optimum wing models with backward facing step stall occurs at 140. The experimental results also show that wing model with the aspect ratio 2 yields the optimum performance as its lift to drag coefficient ratio is higher than any other models. It is also experimented that by introducing backward facing step the flow separation is controlled at high angle of attack which is required during takeoff, landing and maneuvering.