The work investigates the effect of turbulent intensity (Tu) on the force and wake of a NACA0012 airfoil at chord Reynolds number Rec = 5.3×103 and 2×104. 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 identified based on the characteristics of the maximum lift coefficient (CL,max), i.e., ultra-low (Rec 5×106). It is noted that at Rec = 5.3×103 (ultra-low Rec regime) the stall is absent for Tu = 0.6% but occurs for Tu = 2.6% and 6.0%. As Rec increases to low Rec regimes, Tu influence weakens and the critical Rec between the ultra-low and low Rec regimes decreases. When the airfoil attack angle (α) varies from 0° to 30°, at low Tu (0.6%) the shear layers over the airfoil are mostly laminar at the ultra-low Rec regime but involve transition at the low Rec regime. The effect of increasing Tu on the flow bears some similarity to that of increasing Rec, albeit with a difference. The concept of the effective Reynolds number Rec,eff advocated for the moderate and high Rec regimes is re-evaluated for the low and ultra-low Rec regimes. The Rec,eff treats the non-zero Tu effect as an addition of Rec and is determined based on the presently defined Rec,cr. It has been found that all the maximum lift data from both present measurements and previous reports collapses into a single curve in the low and ultra-low Rec regimes if scaled with Rec,eff.