ABSTRACT: Aerodynamic performance of a full span NACA 641-412 airfoil with a circular-shaped damage at various attack directions has been numerically investigated in this study. To assess the aerodynamic effects of different penetration angles in which threats such as projectiles can pass through the wings, attack directions of 30°, 60°, -30° and -60° relative to the normal axis of the chord line has been studied and compared with attack direction of 0°. To validate with published studies about damaged wing, the 200 mm chord airfoil was simulated with the damage hole diameter of 20% chord at the midspan and midchord location in Reynolds number of 500,000. Quantitative and qualitative results of this numerical study had a good agreement with published experimental data due to appropriate structured mesh and turbulence modelling. In addition to lift, drag and pitching moment coefficient, surface pressure distribution around the damage hole has been studied. Results show that, if the penetration angle becomes more negative, aerodynamics performance of the wing will be further decreased; therefore, attack directions of threat mechanisms such as “ahead and above” or “below from the rear” have severe negative impact than other directions on aerodynamic performance of the damaged infinite wing.

ABSTRACT Experimental investigations were carried out to study the wake profile of a supercritical airfoil at Mach numbers of 0.4 and 0.6 in a pitching motion. Both static and dynamic tests were conducted in a tri-sonic wind tunnel. Flow field inside the wake was measured by hot wire anemometry at downstream distances of 0.25 and 0.5 times the chord length from trailing edge. All data were taken at mean incidence angle of 3º; the amplitude of oscillation was 3º and the oscillation frequencies were 3 and 6 Hz. Moreover, numerical study was applied for the same airfoil under similar experimental test conditions; finally, wake profiles obtained from both numerical and experimental methods were compared.

ABSTRACT In this study, incompressible, unsteady and turbulent flow over an airfoil with pitching and plunging oscillations is numerically studied in order to investigate the effect of reduced frequency on stability derivatives of oscillating airfoil. Linear k – ε model called Launder-Sharma and Rhie and Chow model are used for turbulence modeling and overcoming pressure checkerboard problem. This means that a co-located approach is proposed in this paper to study a moving grid problem, and the results demonstrate the high accuracy of the method. Control volume and Crank-Nicholson discretization method are also used for the numerical solution. It is shown that the longitudinal stability derivatives of plunging and pitching motions trend change intensively beyond the stall angle of attack while pitching rate has a completely opposite behavior. The results also show that increasing reduced frequency leads to stability reduction in plunging oscillation but it does not have significant effect on pitching oscillation case in pre-stall, stall and post-stall conditions. Grid convergence is examined to assess the accuracy of the numerical method that shows the high accuracy of it and this is a prominent achievement of the present study. The results of the proposed method in forces and moment show a good agreement with the experimental data.