Previous Up Next

2.6  Starting vortex of a NACA 2414 aerofoil

G. D. McBain
sh n2414 6 | gfsview2D starting.gfv
Required files
starting.gfs (view) (download) starting.gfv n2414.dat
Running time
5 minutes

According to Wikipedia a ‘Starting vortex’

is a vortex which forms in the air adjacent to the trailing edge of an airfoil as it is accelerated from rest in a fluid. It leaves the airfoil…, and remains (nearly) stationary in the flow.

Or in the frame of reference of the aerofoil, it appears to recede behind the wing. The phenomenon is fundamental to the understanding of the generation of lift by aerofoils; see e.g. [2] (Figure 69, p. 121) or [12] (Figure 1.5, p. 21).

A starting vortex is easily generated in a Gerris simulation, as shown here. It does not depend for its existence on the viscosity of the air, or the third dimension, so here we solve the two-dimensional Euler equations.

The phenomenon does depend on the trailing edge being sharp, as it is for most aerofoils. There is a great collection of such shapes at the UIUC Airfoil Coordinates Database. The coordinates from these files can be converted to a Gerris solid surface using the Gerris command line utility shapes. Here we use a classic aerofoil, the NACA 2414 [5], from n2414.dat.

Static refinement around the wing section is necessary to capture the shape well in a Cartesian quad-tree grid. The grid is also adaptively refined on the vorticity to resolve the trailing vortex as it recedes into the wake.

Figure 12: Generation of a starting vortex in plane flow over a NACA 2414 aerofoil at 6 incidence. The colour is vorticity (red positive anticlockwise).

Previous Up Next