Experimental Investigation of the Unsteady Aerodynamics of a Pitching S809 Aerofoil at Various Reduced Frequencies and High Reynolds Numbers

This paper presents first experimental results on the unsteady lift and pitching moment coefficients of an oscillating S809 aerofoil at Reynolds numbers up to \(6 \times 10^{6}\). The model can perform sinusoidal pitching motions with amplitudes up to \(\pm 15^{o}\) at reduced frequencies as high as \(k = 1\), independent of its mean angle of attack. For the steady model configuration the aerodynamic loads at angles of attack of \(-30^\circ \le \alpha \le 30^\circ \), hence including the deep dynamic stall, are investigated. It is shown that in this range an increase in Reynolds number from \(0.5 \times 10^{6}\) up to \(6 \times 10^{6}\) has a clear effect on the maximum lift coefficient and the stall behaviour. However, in case of sinusoidal pitching at \(\hbox {Re}_{{c}} = 4 \times 10^{6}\) and \(6 \times 10^{6}\) only small influences of the Reynolds number on the dynamic stall are observed. Higher reduced pitching frequencies and/or larger amplitudes then again lead to an increasingly pronounced dynamic stall.