Unsteady crossflow on a delta wing using particle image velocimetry

Abstract

5has shown that the vortex breakdown response is typically an order of magnitude slower than the convective time scale; in essence, this means that the location of breakdown substantially lags that expected from quasistatic considerations. In view of these observations of the phase lag of vortex breakdown location, one expects the cross-sectional development of the leading-edge vortices to exhibit an analogous phase lag. Such lag has been demonstrated using qualitative flow visualization.6 For this type of lag, the overall features of the velocity field during pitching maneuvers have been characterized separately.5 Therein, the velocity field at several instants during the wing motion is compared with its quasistatic counterpart to show the consequence of the movement of the location of vortex breakdown through the plane of interest. The unsteady loading in relation to the foregoing features of the flow structure has been reviewed independently7 and illustrates that corresponding phase lags and hysteresis of the unsteady forces are induced during a typical maneuver. The emergence of particle image velocimetry (PIV) provides the potential for detailed characterization of the unsteady velocity field past a moving delta wing with an accuracy comparable to laser-Doppler anemometry (LD A) but without the necessity of phase referencing. This high-resolution optical method allows detailed definition of the flow structure at a given instant, thereby providing a more accurate representation of the flowfield than can be accomplished with phasereferencing techniques. The objective of this note is to report on the first characterization of the unsteady flow structure past a pitching delta wing via particle imaging techniques and to reveal new features of the flow structure during pitch-up and pitch-down maneuvers. The major challenge of applying PIV to this class