Wind tunnel experiments of multijets in cross flow: Effect of the injection ratio

The triple jet in cross flow problem has been handled experimentally in the present work for its wide presence in several industrial and environmental applications. Different injection ratios and heights have been considered in the case of three inline inclined jets discharged in an oncoming cross flow generated within a wind tunnel. The jets were discharged from cylindrical ducts that were razed at different levels from the ground which gave rise to elliptic cross-sections characterized by a little and great diameters. Hot wire anemometry was used to ensure of the independence of the jet nozzles' location on the interacting flows' mixing while the particle image velocimetry technique was adopted to track the different jets' progression within the domain. The observation of the different extracted experimental data (velocity and vorticity vectors and contours, streamlines, jets' trajectories etc.) revealed the complementarity of the effect of the injection ratio and height. In fact, the augmentation of both parameters helped straighten the jets, decrease the pressure drop between the discharging nozzles, reduce the entrainment of the upstream jets and straighten their velocity trajectory. However and concerning the impact of the injection ratio that varied between 0.5, 1 and 2, it was obvious that the intermediate value of R = 1, was critical as it corresponded to jets and mainstream with comparable forces that complicated furthermore their confrontation. The major vortices that were observed on the symmetry plane included the wake vortices that were most apparent for weaker injection ratios due to the pronounced reattachment to the tunnel ground. The second observable vortices in the symmetry plane are the leading edge vortices that develop at the upper periphery of the jets as a reaction to their entrainment of the mainstream, and that are most striking along the leading edge of the let jet due to its most consistent deflection by the mainstream.