The present cross-wire measurements of the flowfield above a 75-deg flat-plate delta wing have yielded distributions of velocity, axial vorticity, and circulation which exhibit strongly conical behavior upstream of the breakdown region and away from the apex and trailing edge regions. The conical character of these properties is most pronounced over the central portion of the planform, away from the apex and trailing-edge regions. This behavior is further documented by the roughly linear increase in vortex strength with distance from the apex over the forward area of the wing.

Measurements of Circulation and Vorticity in the Leading-Edge Vortex of a Delta Wing

Turbulent and unsteady flow characteristics of delta wing vortex systems

A Comparison of Data-Reduction Methods for a Seven-Hole Probe

The interaction of vortex breakdown with an oscillating e n was investigated by e ow visualization and velocity measurements to understand the effects of aeroelastic dee ections on e n buffeting. For frequencies lower than a cutoff frequency, the response of vortex breakdown location is quasi periodic, and the amplitude of the variations of breakdown location decreases with increasing frequency. For frequencies higher than the cutoff frequency, vortex breakdown does not respond to the e n oscillations. These observations suggest that the dynamic response of breakdown location to an oscillating e n is similar to that of a low-pass e lter. For different locations of the e n with respect to the vortex, similar amplitude responses were found. This result can be used in the design of e ns to prevent a feedback effect and coupling between the vortex breakdown and e n structure. A theoretical explanation of the experimental observations based on the wave propagation characteristics of the vortex e ows is presented.

Interaction of Vortex Breakdown with an Oscillating Fin

The transient flowfield over a delta wing during pitch-up motions to very large angles of attack was investigated. Emphasis was directed at the growth and the eventual breakdown of the leading-edge vortices. Delta wing models were tested in a wind tunnel at Reynolds numbers of order 10 5 . The flowfield along the trailing edge was mapped out via a seven-hole probe designed, constructed, and calibrated to general time-resolved information. Instantaneous surface pressure measurements were also obtained. Earlier qualitative evidence of hysteresis in the development of the flow was confirmed. Moreover, the present data indicate significant differences of vorticity content between the steady and the steady motions, for reduced frequencies as low as 0.01

Dynamic pitch-up of a delta wing

This paper discusses the use of a seven-hole probe on measurements of leading edge vortices of highly sweep delta wing planforms. Intrusive probe data taken with the pressure probe were compared with nonintrusive measurements made with laser Doppler anemometry system. In addition to probe size, the natural position of breakdown and the sweep angle of the wing are also factors in determining sensitivity of the flow to probe interference. At low angles of attach vortex breakdown does not occur in the vicinity of the model and the seven hole probe was found to yield reasonably accurate measurements. When the angle of attack of the model was increased so that vortex breakdown was near the trailing edge, introducing the probe over the wing would cause the breakdown position to move ahead of the probe. However, when breakdown naturally occurred ahead of the mid-chord of the wing the vortices were found to be less sensitive to a probe placed behind the breakdown point. Vortex breakdown on a lower swept wing is found to be more sensitive to interference. Near the breakdown region, seven hole probe measurement is less accurate due to a combination of probe interference and flow reversal.

F. M. Payne

Papers

Seven hole probe measurement of leading edge vortex flows