Three-Di mensional Computations of Multiple TandemJets in Crossflow

The mixing and merging characteristics of multiple tandem jets in crossflow are investigated by use of the Computational Fluid Dynamics （CFD） code FI,UENT. The realizable k - ε model is employed for turbulent elosure of the Reynolds-averaged Navier-Stokes equations. Numerical experiments are performed for 1-, 2- and 4-jet groups, tbr jet-tocrossflow velocity ratios of R = 4.2 ～ 16.3. The computed velocity and scalar concentration field are in good agreement with experiments using Particle Image Velocimetry （PIV） and Laser Induced Fluorescence （LIF）, as well as previous work. The results show that the leading jet behavior is similar to a single free jet in crossflow, while all the downstream rear jets have less bent-over jet trajectories - suggesting a reduced ambient velocity for the rear jets. The concentration decay of the leading jet is greater than that of the rear jets. When normalized by appropriate crossflow momentum length scales, all jet trajectories follow a universal relation regardless of the sequential order of jet position and the nund）er of jets. Supported by the velocity and trajectory measurements, the averaged maximum effective crossflow velocity ratio is computed to be in the range of 0.39 to 0.47.

Swirl Jets in Crossflow at Low Velocity Ratios

This investigation examines experimentally the behavior of swirled jets produced by axial flow fans blowing into a crossflow at low velocity ratios. The main difference with non-swirl cases is an asymmetry of the dominant kidney vortex and a slight distortion of the jet trace downstream of the injection hole. The effect of jet rotation at relatively low swirl numbers and similar velocity ratios is also investigated by a validated computational analysis tool. The numerical results are analyzed by means of various post-processing procedures, aiming to clarify, quantify and analyze the impact of swirl on the characteristics and the flow domain of a jet in crossflow. In general, swirl introduces an asymmetry in all examined quantities and prevents the penetration of the jet into the crossflow, causing the jet to remain closer to the wall surface. The rotation of the injected fluid results in an imparity of the two parts of the Counter Rotating Vortex Pair （CVP） which is no longer symmetric to the axial centerline plane. High swirl numbers result in the destruction of the CVP and the dominant kidney shape vortex is transformed into a comma shape vortex, rotating close to the wall.

ON THE SELF-SIMILARITY OF A JET IN CROSSFLOW

The RNG k εturbulence model is adopted to investigate a turbulent round jet issuing into crossflow, with the Reynolds number at jet exit of Re=6000 and jet to crossflow velocity ratio of r=8. With the CFD code, FLUENT, the relations of dimensional analysis are successfully reproduced and the calculated coefficients agree well with the experimental measurements of Wong (1991) and Chu (1996). The investigations are then taken on the velocity, stream function and vorticity at the far field of the jet. It shows that at least within the covered range herein, the jet at the far field is self similar.