Experimental investigation of the influence of wing sweep on juncture flow
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Date
1994
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Abstract
Influence of wing sweep on juncture flow has been investigated using three component laser Doppler velocimetry and body-surface pressure measurements. Configurations with forward and back sweep angles of 7.5 degrees, 15 degrees, 22.5 degrees, 30 degrees, and 45 degrees were studied. Comparisons were made with a zero-sweep wing-body juncture. A multi-vortex system transitioning with increasing Reynolds numbers from a static three-vortex system (Mode I) to an oscillating three-four vortex system (Mode II) and finally to a three-four vortex shedding/splitting system (Mode III) was observed. Increase in back-sweep angle delayed the transition to the higher modes and modified Mode III behavior. Strengthening of the vortex-system up to +15 degrees back-sweep angles was observed as an increased pressure difference between the local extrema in the plane of symmetry on the body-surface and maximum backflow mean velocity. With increasing forward-sweep, the vortex-system was less observable as fully formed in the plane of symmetry. However immediately outside the region of influence of the spanwise flow along the attachment line, the vortex system was seen to be fully formed. Additionally a strong counter-rotating vortex closwer to the wing was also observed. Variation of horizontal location of the vortex in the transverse planes with changes in sweep angle was in contrast to that suggested by the surface flow patterns. In these planes the vortex lifted up higher for forward-swept wings and was insensitive to changes in sweep angle compared to back-swept configurations. Larger portions of the wing leading-edge were contaminated by the turbulence in the separated flow for increasing back-sweep angles. Relatively lower levels of turbulence in the separated flow for increasing back-sweep angles. Rleatively lower levels of turbulence were noted in the plane of symmetry of the forward-swept configurations. Unsteady nature of flow in the juncture was observed in the form of multi-modal velocity histograms but was limited to regions much closer to the body-surface for forward-swept wings as compared to other configurations.
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Major aerospace engineering