Experimental Investigation of the Jets in Crossflow: Nonswirling Flow Case

The mixing of eight isothermal jets issuing in a fully developed circular pipe How is investigated by means of laser Doppler anemometry, particle image velocimetry, and planar laser induced fluorescence techniques. Two values of the momentum ratio are considered. Unsteady and steady flow patterns are analyzed, Characteristic frequencies are deduced from spectral analysis. Velocity and scalar concentration fields are compared. The mean centerline concentration decay is characterized. The analysis of the flow instabilities is focused on the wake-type structures downstream of the jets and the shear layer structures appearing between the jet and the main flow. The results on the wake-type structures are consistent with previous observations done on a single jet. In particular, the influence of the velocity ratio on the signal-to-noise ratio is confirmed. The Strouhal number associated with the shear layer structure depends on the velocity ratio and on the Reynolds number. The comparison between the velocity and concentration fields confirms the difference in the jet trajectories deduced from these two fields. The detailed analysis of the concentration field gives useful information on the influence of the confinement on the jets' behavior.