The Study On Mixing Characteristics Of A Tandem Multiple Jet Group In Cross-flow

The mixing and merging characteristics of a tandem multiple jet group in cross-flow are investigated using the Laser Induced Fluorescence (LIF) technique, the Particle Image Velocimetry (PIV) and the Computational Fluid Dynamics (CFD) code FLUENT. The main works are shown as follows:1. LIF technique and PIV technique are selected to study the concentration and velocity field of a tandem multiple jet group in cross-flow. The corresponding experimental setups are established. The experimental details, which should be paid attention to, are listed as well.2. The numerical model is established based on the Fluent code. The standard k ~ ε model and realizable k ~ ε model is employed for turbulent closure of the Reynolds-averaged Navier-Stokes equations.3. The computed results of two k ~ ε models are compared with the experimental data of a momentum jet in cross flow by Sherif and Pletcher (1989). It is found that the results by realizable k~ ε model are superior to the results by standard k~ε model. Then, the realizable k ~ ε model is selected to simulate mixing characteristics of a tandem multiple jet group in cross-flow.4. The concentration and velocity results by LIF technique, PIV technique and numerical model respectively, such as concentration centerline trajectory, dilution and velocity, are compared. The good agreements between the computed results and the experimental results are acquired.5. The concentration and velocity centerline trajectories are studied. The results show that the leading jet behaves similar to a single free jet in crossflow, while all the downstream rear jets have higher and very similar jet trajectories - suggesting a reduced ambient velocity for the rear jets (effective cross-flow velocity). The concentration decay of the leading jet is greater than that of the rear jets. When normalized by the momentum length scales l_m~* based on average effective cross-flow velocity, when y /l_m < 1, all jet trajectories follow a universal relation regardless of the sequential order of jet position and the number of jets. In logarithm coordinate system, all jet trajectories follow the 1/2 power relation when y /l_m < 1 and the 1/3 power relation when y /l_m > 1 respectively. The equations of all jet trajectories are built.6. The velocity fields in different cross-sections are studied. The interactions between different jets, jets and cross-flow are analyzed.7. Based on the concentration, velocity and vortex fields, the developingprocesses of horseshoe vortex and kidney counter-rotating vortex pair arc studied. The influence of multiple jets is analyzed.8. The dynamic pressure fields in different cross-sections are studied. The reason making jet bend is analyzed.