Comparative Assessment on Unsteady Aerodynamics of Thin and Thick Airfoils Subjected to Pitching Motion

Abstract

This article presents the comparison between the unsteady flow characteristics of thick (t/c ≥ 6%) and thin (t/c ≤ 6%) airfoils performing pitching motion at Reynolds number Re = 3.6 × 10 5 . For the analysis, the considered airfoils are NACA 0012 as thick and symmetric airfoil and GOE 417A as thin and highly cambered airfoil. The analysis in this study is restricted to only two airfoils because from the preliminary investigations, similar aerodynamic characteristics with slight variation in their flow field development under same conditions were observed. The influence of reduced frequency, pitching amplitude and mean angle of attack on the airfoil’s aerodynamic performance in terms of instantaneous force coefficients is thoroughly investigated. Further, the flow surrounding the airfoils is also investigated. It is noticed that the aforementioned parameters substantially affect the instantaneous force coefficients (both qualitatively and quantitatively). Under certain conditions, the formation of reverse Karman vortex street was observed indicating airfoil’s thrust force generation. It must be noted that the conditions where the thrust force generation occurs for thick and symmetric airfoils like NACA 0012 are quite different from that of thin and cambered airfoils like GOE 417A. Additionally, a drastic change in the flow field around the airfoils is observed under similar conditions. For NACA 0012 airfoil, the formation and convection of the Leading Edge Vortex (LEV) under certain conditions has detrimental effects on its aerodynamic characteristics as it encourages early flow separation. However, the same cannot be true for thin and highly cambered airfoils like GOE 417A. Under the similar conditions with negligible variation, the LEV contributes toward providing extra suction over the GOE 417A airfoil’s suction side. This significantly improves airfoil’s aerodynamic characteristics.