A powerful flow visualization based on a laser-sheet and the quantification of the intensity of the light
from Mie scattering had been introduced and successfully used to evaluate the statistics and spatial
correlations of gas distribution injected into a two-dimensional turbulent recirculation airflow, utilizing a
backstep configuration. In the experiment the free stream velocity was, U, = 10 m/s and the step height
was, H = 20 mm. The study focussed on the _fluctuation and the gas distribution in the recirculation zone
in order to elucidate the gas-air moving characteristics. The results show that the distribution of injected
gas shows different trends depending on the location of injection. When the specific momentum of
injection is increased the maximum fluctuation level of the gas concentration decreases. A reduction up
to 30 % of the maximum RMS value of luminance intensity _fluctuation can be observed when increasing
specific momentum ratio of injection from 0. 04 to 0.3. Spatial correlations suggested that mixing between
injected gas and surrounding air was more rapid and better in case injection in the near reattachment
point due to higher turbulence in the region.
