Experimental investigation of the flow structures over a 40° swept wing

Abstract

Flow 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.

Laminar separated flows over finite-aspect-ratio swept wings

“…The resulting flows resemble the ‘tip stall’ phenomenon, as described in Black (1956), Zhang et al. (2019) and Visbal & Garmann (2019). This type of flow, as indicated by yellow squares in figure 3, prevails for swept wings with large aspect ratios (e.g.…”

“…With the gradual weakening of the midspan effects towards the outboard sections, unsteadiness develops locally near the tip region, while the midspan region still remains steady. The resulting flows resemble the 'tip stall' phenomenon, as described in Black (1956), Zhang et al (2019) and Visbal & Garmann (2019). This type of flow, as indicated by yellow squares in figure 3, prevails for swept wings with large aspect ratios (e.g.…”

“…The stalled flow over a swept wing usually features a 'ram's horn' vortex, which stems from the inboard leading edge and grows in size as it trails to the wake behind the tip. Such unique flow is also referred to as 'tip stall' (Black 1956;Zhang et al 2019). Focusing on the detailed flow structures, Yen & Hsu (2007) and Yen & Huang (2009) experimentally studied the effects of sweep angle, Reynolds number (Re) and angle of attack on the wake vortices, boundary layer flow patterns and aerodynamic performance of swept wings.…”

“…Such unique flow is also referred to as ‘tip stall’ (Black 1956; Zhang et al. 2019). Focusing on the detailed flow structures, Yen & Hsu (2007) and Yen & Huang (2009) experimentally studied the effects of sweep angle, Reynolds number () and angle of attack on the wake vortices, boundary layer flow patterns and aerodynamic performance of swept wings.…”

Wingtip vortex structure in the near-field of swept-tapered wings

“…Such experimental campaigns [31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] have primarily been restricted to wings of simple rectangular planform, conducted to investigate the dynamics of the tip vortex formation around the wingtip and its development as it propagates through the near-field. Considerably fewer in number, other investigations have examined the vortex system shed from platforms which are both swept and tapered and therefore more analogous to that of commercial aircraft [47][48][49][50][51][52][53][54] . Of these experimental studies, very little information is provided regarding the behaviour, structure, or development of the vortex core due to limitations in the spatiotemporal resolution available from the experimental diagnostics employed (e.g.…”