Q., "Experimental investigation of the flow field of an oscillating airfoil and estimation of lift from wake surveys", Journal of Fluid Mechanics, Vol. I., "Hot-Wire Measurement of Near Wakes Behind an Oscillating Airfoil", AIAA Journal, Vol. Lee, T., and Gerontakos, P., "Investigation of flow over an oscillating airfoil", Journal of Fluid Mechanics, Vol. and Maresca, C., "Unsteady boundary-layer measurement on oscillating airfoils: transition and separation phenomenon in pitching motion", AIAA paper 96-0035. T., "On the Wake of a Pitching Airfoil", AIAA Paper 85-1621, 1985 V., "Wind tunnel tests of wings at Reynolds numbers below 70,000", Experiments in Fluids, Vol. "A Guide to Uncertainty Analysis of Hot-wire Data", Journal of Fluids Engineering, Vol. M., Viscous Fluid Flow, McGraw-Hill International Edition. Goldstein, S., ed., Modern Developments in Fluids Dynamics, Vol. W., "Near-Wake Characteristics of an Oscillating NACA 4412 Airfoil", Journal of Aircraft, Vol. R., "Velocity Measurements over a Pitching Airfoil", AIAA Journal, Vol. W., "Progress in Analysis and Prediction of Dynamic Stall", Journal of Aircraft, Vol. J., "Analysis of the Development of Dynamic Stall Based on Oscillating Airfoil Experiments", NASA TN-8382, 1977Ĭarr, L. P., and Dulieu, A., "Vortex formation around an oscillating and translating airfoil at large incidence", Journal of Fluid Mechanics, Vol. Unsteady Flow Concepts", Journal of Fluids and Structure, Vol. P., "Fluid Mechanics of Dynamics Stall Part 1. A NACA 0012 airfoil was sinusoidally pitched at the quarter chord point with an oscillating amplitude of $10^4$ 사이에 상당한 차이가 있다는 것을 나타낸다.Įricsson, L. All rights reserved.An experimental study was performed in order to investigate the influence of Reynolds number on the drag coefficient variations of an oscillating airfoil. The phase of the shear layer motion with respect to the airfoil motions shows a clear difference between the exciting and the damping case.
On the other hand, the shear layer formed after separation is found to clearly move periodically away from the airfoil suction surface and towards it with a phase lag to the airfoil oscillations. Particle Image Velocimetry (PIV) measurements of the flow around the oscillating airfoil show that the shear layer separates from the leading edge and forms a leading edge vortex, although it is not very clear and distinct due to the low oscillation amplitudes. Outside this range of reduced frequencies, the energy transfer is negative and under these conditions the oscillations would be damped. These measurements indicate that for large mean angles of attack of the airfoil (alpha(m)), there is positive energy transfer to the airfoil over a range of reduced frequencies (k=pi fc/U), indicating that there is a possibility of airfoil excitation or stall flutter even at these low Re (c=chord length). The unsteady loads on the oscillating airfoil are directly measured, and are used to calculate the energy transfer to the airfoil from the flow. The airfoil is placed at large mean angle of attack (alpha(m)), and is forced to undergo small amplitude pitch oscillations, the amplitude (Delta alpha) and frequency (f) of which are systematically varied.
In the present work, we experimentally study and demarcate the stall flutter boundaries of a NACA 0012 airfoil at low Reynolds numbers (Re similar to 10(4)) by measuring the forces and flow fields around the airfoil when it is forced to oscillate.
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