On the Coupling Between Adjacent Turbulent Jets

A detailed examination of the coupling observed between adjacent turbulent jets, one of which was externally excited, is presented. The study is relevant to the active control of combustion and mixing devices; applications which demand maximum reliability and minimal power consumption by their active elements. To this end, it is desirable for each active component to affect several simple, non-active components in the system. An initial study of three collinear turbulent air jets was seen to enhance the mixing of adjacent, unforced jets with ambient fluid by 15–20%. The work presented here examines this phenomena using quantitative PLIF mixing measurements, three component and single-wire velocity measurements, qualitative flow visualization, and reduced singular value decomposition (SVD). This analysis of the data shows that the mixing improvement in the adjacent, unforced jets is primarily due to the low level perturbation at the exit of the unforced jets induced by the periodic forcing in the active center jet. This improved mixing is shown to be a result of amplification of the +/-1 spatial mode. Large scale structures in the central, forced jet are shown not to effect the behavior of the adjacent jets.