The significance of coherent flow structures for the turbulent mixing ...

5.2 Experimental set-up
α4 α3
α2
α1
main flow-direction
4
test-section
3
x
2
side window
z
1
FIGURE 5.1: Schematic set-up of the double stereoscopic recording system installed 18 m behind the
leading edge of the flat plate for the investigation in the stream-wise wall-normal plane (not in scale).
Four digital cameras (1-4), mounted on Scheimpflug-adapters, observe opQq the tracer particles which
are illuminated from below the test section (rs À scattering angle) by means of four synchronised lasers
which deliver two intense green light pulses with t#uBv¥w¥o nm.
by 1024 pixel resolution and 12 Bit dynamic range have been employed, each connected
with a Scheimpflug-adapter in order to adjust precisely the angle between the image-, objectand
main-plane of the lens according to section 3.1.2. The imaging of the field of view was
performed by means of 180 mm Carl Zeiss lenses with an aperture of 8 in order to avoid depth
of focus effects and optical aberrations introduced by the 10 mm glass-walls of the windtunnel,
see section 4.7. This allows to benefit from the high performance of the correlation
algorithms, according to section 2.4, as the particle images appear as bright circles, 2-3 pixel in
camera 9 [mm] x [mm]
â
?nm
[mm] [deg]
1 -1109 1459 1838 37.5
2 -1109 -1478 1848 36.9
3 -1051 1462 1801 35.7
4 -1038 -1473 1802 35.2
TABLE 5.1: Position and observation distance of the four cameras with respect to the centre of each
field of view (intersection point of optical axis) and observation angles. Distance between centre of
adjacent observation areas: 85 mm. Distance between camera one and three: 156 mm.
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