An Experimental Investigations of the Oscillations of an Airfoil Near a Sharp Velocity Gradient

Citation

Walker, Donald Petrilla (1951) An Experimental Investigations of the Oscillations of an Airfoil Near a Sharp Velocity Gradient. Engineer's thesis, California Institute of Technology. doi:10.7907/5PMF-4R60. https://resolver.caltech.edu/CaltechETD:etd-03232009-090843

Abstract

The purpose of this study was to make an experimental investigation of the effect of a sharp velocity gradient on the oscillations of an airfoil. This information is pertinent to the formulation of theories for predicting tail buffeting. The test equipment was designed to provide conditions corresponding as closely as possible to those based on the assumptions of Lo in his theoretical study of an oscillating airfoil in parallel streams separated by an interface.

Because of the viscous nature of air, the assumptions of Lo could not be simulated sufficiently closely to permit an experimental check on his findings. The simulation, however, was adequate to provide for an experimental check on his fundamental point of view as an explanation of buffeting.

The presence of the high speed flutter predicted by theory was verified. Variations in the flutter speed and flutter frequency were noted as the position of the sharp velocity gradient relative to the airfoil was shifted, but these variations were not considered significant.

A low speed oscillation was found which the evidence available indicated was due to periodic vortices formed in the flow by the experimental set-up used to create the velocity gradient. Limitations on the minimum operating speed of the wind tunnel precluded a thorough investigation of the lower speeds in the low range.

The evidence found in this investigation, though not conclusive, indicates that buffeting is simply the response of an elastic system to a turbulent flow. No conclusive evidence was found to indicate that a sharp velocity gradient near an airfoil has any effect on the oscillations of the airfoil.

Further investigation of the airflow created by the experimental set-up used is recommended in order to explain precisely the oscillation phenomena encountered.

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