>

2. Experimental facility

Experiments have been carried out in a plane two-dimensional wall-jet shown in Figure 1. The wall jet was driven by a centrifugal fan, allowing for exit velocities u_j up to 55 m/s. The Reynolds number based on the jet exit velocity u_j and the slot width b = 8 mm ranged from Re_j = 2500 to Re_j = 10000. At Re_j$\ge$10000 the turbulent wall jet is self-preserving in the region of 40 $\leq$ x/b $\leq$ 150 with respect to the mean and turbulence quantities, as shown, for instance, by [Abrahamsson, Johansson & Löfdahl (1994)] and [Schober (1999)]. The slot width b of the wall jet was adjustable, but was kept constant at 8 mm throughout the experiments presented in this paper. The jet exit was mounted flush with the test section wall. The slot spanned the whole test section, which had a width of 490 mm.

A thin wire was stretched parallel to the wall-jet exit to manipulate the shear layer originating at the nozzle (see figure 1). By varying the tension of the wire the eigenfrequency could be changed. Strain gauges, mounted on the support prongs, enabled the determination of the wire frequency.

Figure 1: Wall-jet unit.

An electrically heated constantan wire was placed in the settling chamber of the wall jet (see figure 2). Paraffin oil droplets along the wire produced a sheet of oil vapour in the settling chamber. The position of the smoke wire in the settling chamber, where the velocities are small, allowed flow visualisation at the comparably high exit velocity of u_j $\approx$ 10 m/s.

Figure 2: Smoke wire setup.

The positions of the camera and the light source are shown in figure 2. The background was covered with black velvet to reduce light reflections. A stroboscopic lamp was used to freeze the motions of the vortices.

Drupal 7 Appliance - Powered by TurnKey Linux