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Knowledge of the instantaneous flow behaviour of interacting opposing jets, in addition to knowledge of the mean flow, is important for science and practice. Whereas studies often focused on axisymmetric jets, analyses for plane jets are scarce in general and for plane jets in an enclosed domain (i.e. not a (semi-)open environment) in particular, as e.g. encountered in airplane cabin ventilation. In this paper, 2D particle image velocimetry measurements are performed to study isothermal interacting opposing plane wall jets and plane free jets in a generic empty reduced-scale water-filled enclosure. Inlet Reynolds numbers vary from 3450 to 4650. The analyses encompass an inspection of the global flow patterns (in the vertical midplane) and of the flow components (e.g. interaction zone, merged jet, return flows, recirculation cells), using distribution plots, correlation functions and fast Fourier transforms. Vortical structures are also visualised and tracked over time. It is shown that the transient interaction of the opposing wall jets drives a merged jet that resembles a flapping turbulent plane jet. Remarkable are the occasional deviating (more unstable) flow patterns that appear. Furthermore, many vortical structures are present that could enhance mixing within the enclosure. The opposing free jets mainly show quasi-periodic oscillations with a given frequency (Strouhal number around 3.3 × 10–3), comparable to opposing plane free jets mentioned in the literature. Also in this configuration, many different vortices are present that can grow considerably large while transported through the flow domain. Both configurations show a potential for contaminant lock-up (stagnation zones). |
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