Abstract
The work investigates the effect of turbulent intensity (Tu) on the force and wake of a NACA0012 airfoil at chord Reynolds number Rec = 5.3X103 and 2X104. Lift and drag coefficients (CL and CD) on and flow fields around the airfoil were measured with Tu varied from 0.6% to 6.0%. Four Rec regimes are proposed based on the characteristics of the maximum lift coefficient (CL,max), i.e., ultra-low (Rec < 104), low (104 〜 3X105), moderate (3X105 〜 5X106) and high (> 5X106) Rec. It is noted that at Rec = 5.3X103 (ultra-low Rec regime) the stall is absent for Tu = 0.6% but occurs for Tu = 2.6% and 6.0%. In the low Rec regime, the Tu influence wanes and the critical Rec, above which stall occurs, decreases with increasing Tu. When the airfoil angle (α) of attack varies from 0° to 30°, at low Tu (0.6%) the shear layers over the airfoil are mostly laminar in the ultra-low Rec regime but involve transition in the low Rec regime. The effect of increasing Tu on flow bears similarity to that of increasing Rec, albeit with a difference. The flow separation shifts upstream with increasing Rec but downstream with increasing Tu.
