Proper orthogonal decomposition based feature identification on a round jet in turbulent cross-flow

The complex interactions that occur within jets in cross-flow can be broken down into different regions of development. By identifying the most energetic regions, the global behavior of the system can be predicted and reconstructed. Experiments are performed in a closed-circuit wind tunnel during which a seeded round jet ejects particles orthogonally into the incoming cross-flow. Turbulence intensity is varied for these experiments using a passive and active grid system where winglets are rotated to excite the cross-flow to compare low and high turbulent inflow. Jet velocity is kept constant and several cross-flow velocities are explored. Mean flow statistics and Reynolds stresses are computed using snapshot particle image velocimetry (PIV) to create instantaneous flow fields and describe jet trajectory. The jet is traced to provide axes normal and tangential to the centerline and the Cartesian data is transformed. These relative instantaneous flow fields are put through proper orthogonal decomposition (POD) analysis to reconstruct Reynolds stresses using only the highest energy modes to highlight the most energetic regions of the jet.