Wind tunnel experiments were conducted on NACA-0015 airfoil model to investigate the effect of the reduced frequency (κ) & Reynolds Number (Re) on the aerodynamic characteristics and hysteresis behavior associated with the pitching motion of the airfoil. Pressure measurements were conducted on the mid span of the airfoil for quantitative results. The hysteresis behavior was observed in aerodynamic characteristics as strong function of reduced frequency in form of a loop which gets enlarged with the increase in the value of reduced frequency. The present investigation of oscillating sinusoidal motion of airfoil, α = 10° + 15° sin(ωt) showed that, under the operating conditions studied, the airfoil was allowed to execute oscillating motion from almost steady (quasi-steady) conditions to unsteadiness with the incremental increase in the reduce frequency. Static conditions show distinct characteristics as compared to dynamic mode. But at extremely low reduced frequency of oscillation even in the dynamic mode the quasi-steady conditions do prevail. This results in a value of reduced frequency upto which the quasi-steady characteristics are preserved. Normal force defect is derived from the surface pressure distribution and the value of reduced frequency within 5% of normal force defect is obtained for varied range of Re to determine and validate the quasi-steady conditions. Re effect is dominant at very low reduced frequency. Also as reduced frequency increases causes decrease in the Re effect and increase in the normal force defect upto certain limiting value. Further increase in the reduced frequency reduces the normal force defect. Effect of Leading edge contamination is also depicted to cause incremental shift in the static stall angle.

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