Turbulent Intensity Effect on Low Reynolds Number Airfoil Wake

The work investigates the effect of turbulent intensity (T _u ) on the force and wake of a NACA0012 airfoil at chord Reynolds number Re _c  = 5.3 × 10³ and 2 × 10⁴. Lift and drag coefficients (C _L and C _D ) on and flow fields around the airfoil were measured with T _u varied from 0.6 to 6.0 %. Four Re _c regimes are identified based on the characteristics of the maximum lift coefficient (C _{L, max}), i.e., ultra-low (Re _c  < 10⁴), low (10⁴ ~ 3 × 10⁵), moderate (3 × 10⁵ ~ 5 × 10⁶), and high (> 5 × 10⁶). It is noted that at Re _c  = 5.3 × 10³ (ultra-low Re _c regime) the stall is absent for T _u  = 0.6 % but occurs for T _u  = 2.6 and 6.0 %. As Re _c increases to low Re _c regimes, the T _u influence decreases. So does the critical Re _c , above which stall occurs. The effect of increasing T _u on flow bears similarity to that of increasing Re _c , albeit with a difference; the flow separation point shifts upstream with increasing Re _c but downstream with increasing T _u .