Experimental investigation on the unsteady lift of an airfoil in a sinusoidal streamwise gust

The unsteady lift of a stationary airfoil encountering a sinusoidal streamwise gust is experimentally investigated under attached flow conditions. The airfoil has an NACA 0015 profile with a chord length c = 0.5 m. The Reynolds number of the main flow is in the range of 198 000 ⩽ Re ⩽ 331 000. The reduced frequency of the perturbation ω ranges from 0.047 to 0.392. The results show that the fluctuation in the lift force reduces very much at the high frequency. It can be attributed to a significant reduction in the fluctuating pressure difference over the front half of the airfoil. Thus experimental aerodynamic admittance functions for the unsteady lift are lower than theoretical predictions relating to this case with increasing reduced frequencies, though experimental values are close to theoretical values at low reduced frequencies.