Abstract
The formation and development of a single vortex is investigated in a wind tunnel. The wake from a lifting rectangular wing based on CLARK-Y profile of 11.7% is studied up to 80 chords downstream. Digital particle image velocimetry is used to measure the velocity field in the cross stream plane from which is the vortex is measured. Two different experimental test were carried out in two different conditions of the tunnel, without and with grid. From the first condition, the vortex is observed to be quite stable and long-lived. A correlation for the peak tangential velocity u θ , max and the vortex core r c has been compared with the Lamb-Oseen model, and it gives a good agreement. The circulation Γ is observed to be proportional to the free-stream U ∞ (range 8 − 20 m/s) and the angle of attack α (range 1−12 deg). The vorticity ω, however, diffuses over time within the growth of the vortex core r c . This growth can be approached by the Squire model. Apparently, the vortex characteristics become weaker when the experiments are performed under grid turbulence condition. Due to the influence of the grid turbulence, some experiments give inconsistent result. This makes difficult to draw conclusions. However, still some interesting information is found in this case.
Highlights
The wake vortices generated by an aircraft wing have been a subject of interest in this research
Studies have shown that the vortex's strength is directly proportional to the weight, the wingspan, and the speed of the aircraft
The velocity profiles are presented in a non-dimensional way / versus r/c, where represents the azimuthal or tangential velocity, is the main stream velocity, r represents radial distance to the centre of the vortex and c is the wing chord length
Summary
The wake vortices generated by an aircraft wing have been a subject of interest in this research. It has been well known that when an aircraft takes off, its wing generates the required lift force and produces horizontal tornado-like vortices called Wake Vortices or Trailing Vortices, see Figure 1[1,2]. These vortices are long-lived, mostly invisible, difficult to predict, and a severe threat to the following aircraft, especially during taking-off and landing phases. The effect of the ambient turbulence on the vortex instability has been observed by Liu [10,11] His investigation was conducted in a towing tank, measured 18 m long, 1.2 m wide, and 0.9 m deep. The PIV technique always results in a significant number of images that must be further processed[17,18,19]
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