Flow dynamics of multi-lateral jets injection into a round pipe flow

Controlling the mixing field of turbulent jets is an important approach in optimizing practical combustion systems. The use of multi-lateral jets upstream from the nozzle exit to control mixing fields is one particular method. Existing studies have investigated jets into a confined cross-flow (JICCF) for dilution mixing, but there is a paucity of data available on the fundamentals for turbulent mixing capabilities of JICCF. The current study investigates the flow structures and Primary Reynolds number mixing characteristics within a round pipe flow modified by four equi-spaced, lateral side injectors. Experiments are conducted in a primary water jet flow that is modified with smaller jets located one central (axial) jet diameter upstream of the nozzle exit. Flow structures and mixing within the nozzle are non-intrusively characterized using simultaneous planar optical techniques. Planar laser-induced fluorescence is used to measure the scalar mixing of the side and axial jet streams, and particle imaging velocimetry is used to measure the planar velocities. Several cases are investigated with variable primary flow to explore the influence of cross-flow velocity on the induced mixing structures within the nozzle. By varying the momentum ratio, three characteristic flow modes are identified within the primary flow, namely streaming mode, impinging mode, and backflow mode. The impact of these modes on the flow and scalar fields is presented and discussed.