Three-dimensional deflecting oscillation of turbulent planar opposed jets confined in an open cavity under crossflow

In this work, the flow dynamics of two isothermal turbulent opposed water jets issuing from rectangular slot nozzles and confined inside an open cubical cavity with vertical crossflow in a rectangular duct are studied experimentally using time-resolved stereo particle image velocimetry. The turbulent structure and the deflecting oscillation of the colliding jets have been investigated for fixed nozzle separation and a crossflow Reynolds number of 3000 for three jets' Reynolds numbers of Rej = 1500, 3000, and 5000. The probability density function of the fluctuations for the three nondimensional velocity components measured at the mean impingement height of the jets has been calculated for three different positions along the cavity span. The experimental results confirm that as Rej increases, departure from Gaussian behavior has been noted, with stronger skewness and larger scatters observed for Rej = 5000. The oscillation dynamics of the flapping jets has been characterized and examined with high spatial and temporal resolution by identifying phase-averaged velocity and vorticity fields and Reynolds stresses at several specific phases. Analysis shows that the value of Rej plays a significant role in the motion and behavior of the switching jets. A proper orthogonal decomposition (POD) analysis of the coherent structure organization of the turbulent flow has been performed to construct a reduced-order model of the turbulent flow. The results show that the first four POD modes contain about 17% of the total kinetic energy (the first 120 modes up to 79%) and that the complexity of the most energetic flow structures increases with an increase in the Rej number.