Abstract
ABSTRACTFlow over a moderately swept wing is characterised by complex localised flow vortex topologies such as ‘closed’ separation bubbles or ‘open’ separation structures. A model of a complex cambered, twisted, tapered wing with 40° leading edge sweep, representative of those designed for manoeuvre at high subsonic Mach numbers, was investigated using the oil-film visualisation, stereo particle image velocimetry and force moment measurements. Wind-tunnel tests were conducted at a range of Reynolds number from 2.1×105 to 8.4×105 and at angles of incidence from −1° to 22°. Still images combined with video clips enable flow patterns over the wing model to be interpreted more clearly and accurately. Using successive images extracted from the video of flow visualisation, the movement of the oil pigment has been estimated. The influence of the Reynolds number and incidence angle was discussed through analysing the flow pattern over the wing surface. Additionally, the link between the flow structures present and the wing aerodynamic performance was studied.
Highlights
Swept wings are widely used in most modern aircraft, especially in manned combat aircraft and unmanned aerial vehicles (UAVs) designed for operation at high subsonic Mach numbers
The flow over a 40° swept wing has been investigated at a range of angles of incidence and Reynolds numbers by using extensive surface flow visualisation and particle image velocimetry (PIV) measurements
The flow topology is revealed in great details after a systematic interpretation of the flow features present
Summary
Swept wings are widely used in most modern aircraft, especially in manned combat aircraft and unmanned aerial vehicles (UAVs) designed for operation at high subsonic Mach numbers. The flow over these types of swept wings at incidence is characterised by separation from the leading edge and by complex interactions with the secondary vortical structure and wing tip structures. Haines[1] compares the flow patterns over swept wings with a simple design at low Mach numbers, and identifies a few dominant features, namely the part-span vortex sheet, which originated from near the leading edge near the inboard end of the separation and occurred somewhere along the span and not necessarily near the tip. In 1960, Werlé employed impressive flow visualisation to discover that the vortex swirl velocity
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