Multiple Tandem Jets in Cross-Flow

Abstract

The interaction of multiple tandem jets in a cross-flow has been studied through experiments. Experiments are conducted with 2-8 momentum and buoyant jets discharged into a perpendicular cross-flow. The tracer concentration field is measured by the laser-induced fluorescence technique. The effective cross-flow velocity in between adjacent jets is inferred from the measured trajectory and prediction by a validated Lagrangian model. Particle image velocimetry is also applied to measure the velocity distribution directly. It is found that the effective cross-flow affecting the behavior of the downstream jets is significantly reduced due to the sheltering effect as well as the entrainment demand in the momentum-dominated near field of the leading edge jet. The trajectories of all the jets downstream of the leading jet are found to be similar. The reduction of effective cross-flow velocity for the downstream jets becomes larger as the jet spacing decreases but is found to be independent of the sequential order of jet position or the number of jets in the group. The reduced effective ambient velocity ratio is typically in the range of 0.3-0.7 for jet to ambient velocity ratio of K=4-15, and jet spacing to diameter ratio of s/D=2-15, with an overall mean value of 0.56. Based on the present results, a first-order analysis is presented to predict the trajectory of the multiple tandem jets; the predictions are in good agreement with data of this and previous investigations.