Wind Energy

50 E. Moryń-Kucharczyk and R. Gnatowska
X 1
Guardian Plus
Analyser
Probe
X 2
B
S B B
QCO2 = 5 l/min
U 0 = 8,3 m/s
Fig. 9.1. Schematic presentation of the set-up and nomenclature
The sketch of the bluff-bodies arrangement considered in this paper
(2D case) and the details of experiment performed in wind tunnel [1] by the
use of carbon dioxide as tracer gas were shown in Fig. 9.1.
Such body configuration is known as a tandem. The inter-obstacle gap
was changed in the range of nondimensional values S/B = 0... 6 (obstacle
side dimension B =0.04 m). The results of previous data, contained in
works of Jar˙za & Gnatowska [1, 2], revealed different flow regimes and critical
body spacing (S/B) at which drag coefficient and vortex shedding alter
rapidly reflecting the stability mode change. Numerical simulations showed
overall changes in flow pictures observed for increasing spacing ratio S/B.
The program of this study consists of: measurement of the mean concentration
profiles in the inter-body gap for different body spacing, comparison of
concentration field with aerodynamic characteristics (obtained as a result of
numerical simulation performed in ITM CzUT), and recognition of the role
of vortex structure and related periodical oscillations.
9.2 Results of Measurements
The isolines of mean concentration for various inter-obstacle gap width
(S/B =2, 4, 6), Fig. 9.2, are the first group of results. As one can see from
the above figure the different distributions of CO2 concentration are obtained
in each case. In the case of S/B = 2 the maximum value of mean concentration
replaces out of flow axis with an increase in the distance x1/B. The
region of higher concentration occurs distinctly outside the gap, overshooting
down-stream cylinder. In accordance with [3] such behaviour could indicate
the existence of one-body regime occurring for very small gaps between bodies.
Maximum value of mean concentration is diverted from flow axis with an
increase in the distance x1/B in the case of S/B = 6 too, but for the distances
x1/B > 1 it moves to the centreline of the wake. Distinctly different picture
of the isolines of mean concentration is observed for S/B = 4, what justifies
the determination of this gap width as critical body spacing. In the above