A Visual Study of a Delta Wing in Steady and Unsteady Motion,
FLOW RESEARCH CO KENT WA
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Two delta wings with a leading edge sweep of 45 deg and 60 deg were studied in a towing tank at chord Reynolds number up to 350,000. The wings were pitched about the quarter chord point through typical angles of attack of 15 deg or - 15 deg, with a reduced frequency in the range of 0 to 3. In the steady state flow, dye visualizations revealed the existence of a shear layer near the leading edge that rolls up and forms discrete vortices parallel to the leading edge. These vortices were observed to pair at least once as they were convected downstream. Similar phenomena were observed in the unsteady case, except that the vortices shed from the leading edge were modulated and altered by the unsteady motion, which was an order of magnitude lower in frequency. In general, the unsteadiness delayed separation and promoted hysteresis similar to results obtained in unsteady two-dimensional airfoils.