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Research was performed in a low-speed wind tunnel to examine the evolution of an unsteady three-dimensional tip vortex in near wake of a rectangular NACA 0015 wing oscillating sinusoidally in pitch about its quarter-chord axis. Three-component laser Doppler velocimetry was utilized to acquire the data. Results showed that the average trajectory of the oscillating vortex in the near field is similar with a stationary wing at the mean incidence.

The rollup region of the tip vortex from a rectangular wing of NACA 0015 profile was measured using a laser Doppler velocimetry to study the time-averaged flow structure in highly three-dimensional near-wake region. The vortex core was found to be predominantly due to axial vorticity that is concentrated at the center and approaches a zero value at the outer portion of the vortex. The length and velocity scales of the vortex were also demonstrated to originate from the near wake, with the inner part of the vortex easily reaching a universal state.

An increase in the lift of a pitching airfoil occurs near the airfoil surface on the suction side of a two-dimensional NACA 0015 airfoil pitching at constant angular velocity about its quarter-chord spanwise axis. The lift is caused by the influx of vorticity from the surface due to strong pressure gradient close to the leading edge. A secondary counterclockwise vortical structure is generated below the leading-edge vortex (LEV), causing the shear layer to roll up, forming the dynamic-stall vortex. LEV is formed at larger incidences at high Reynolds numbers due to early transition to turbulence.

The surface pressure measurements on a pitching swept wing in a water channel show that the three-dimensional dynamic hinderance spreads gradually over a slightly swept wing. The phenomenon is less dynamic than the two-dimensional process over an unswept wing. The onset of the dynamic hinderance leads to a spanwise variation of the aerodynamic coefficients. A spanwise periodicity exists in the production of vorticity. The study is conducted on a swept wing of NACA 0015 profile with a back sweep angle of 15 degrees.

Surface pressure measurements on pitching airfoils up to angles of incidence greater than stall angles yield spatially well-resolved pressure distributions that agree well with experimental data. The obtained pressure magnitudes are greater than previous experiments at low Reynolds numbers due to fast initiation of laminar-turbulence in the flow. The experiment is conducted in a water channel which yields Reynolds numbers of 10 to the power 5 at low velocities of about 30 meters per second.

There is not much information available on the use of diaphragm-type pressure transducers for the measurement of unsteady pressures in liquids. A procedure for measuring the dynamic response of a pressure transducer in such applications and correcting for its inadequate response is discussed in this report. An example of the successful use of this method to determine unsteady surface pressures on a pitching airfoil in a water channel is presented.

Measurements of velocity and vorticity fields around a pitching swept wing reveal a larger lift and a more gradual lift drop-off in comparison to that for an unswept wing. The flowfields for the two wings are similar at early angle on incidence and show a clockwise leading edge vorticity. The dynamic stall vortex detaches from the surface of the unswept wing at an incidence of 26 degrees. Whereas, the loss of vorticity and loss of lift after dynamic stall is gradual in case of the swept wing. The time delay of events across the wing span explains the gradual washing away of the vorticity.

Presents information on an experiment regarding evolution of the unsteady tip vortex in the near wake of a rectangular wing oscillating. Details on the experiment; Result of the experiment; Conclusion.

Presents information on a study which examined the vortex dynamics and stall associated with airfoils. Description of the experiment; Result and conclusion.