The current work investigates the swirling flow of a gas fuel injector utilized in the Lean Direct Injection (LDI) combustion system. Planer particle image velocimetry (PIV) measurements and large eddy simulation (LES) numerical analysis are conducted to have a profound understanding of the swirling flow characteristics. Specifically, the impacts of the level of confinement with a rectangular cross-section and different Reynolds number are examined. Increasing the Reynolds number increases the strength of swirling jets and reverse flow region. More significant changes occurred on the mean flowfield due to the confinement effect such as increasing the width of the reverse flow region and increasing/decreasing the size of the recirculation zones which in turn effects the inlet jet penetration. The inlet jet spreads at a larger angle as the size of the outer recirculation zone (ORZ) increases with the confinement ratio. The shape of the inner recirculation zone (IRZ) vortex structure on the unconfined flow is characterized to be a thin and short vortex and located on top of the nozzle exit, and it becomes thicker and longer vortex located further downstream from the nozzle exit upon confinement. The increased size of the IRZ vortex structure in confined cases is an indication of the increased thickness of the inner shear layer (ISL) that increases linearly as the confinement ratio increases. LES results reveled there is a connection channel between the reverse flow region and the ORZ of the swirling flow emanating from the multiple-jet LDI nozzle. Higher level of turbulence is associated with the location of the IRZ vortex structure. Proper orthogonal decomposition (POD) analysis is preformed to extract coherent fluctuating flow features. The swirling flow of the LDI nozzle exhibits the single-helical and double-helical precessing vortex core (PVC) modes, with the first one being the most energetic mode. The general flow structure of the coherent single-helix PVC mode on the unconfined flow consists of four vortices: two corner vortices rotating in opposite of each other, and a tiny vortex on top of the nozzle exit followed by a huge central vortex rotating in a different direction. Upon confinement the outer vortices attached to the wall of the combustor and the central vortex becomes about twice bigger. The preexistence of the outer vortices on the unconfined flow suggests that the formation of the ORZ is not caused by the confinement, but rather it is a part of the natural behavior of a highly turbulent swirling flow which magnified in the case of confined environment. The single-helix PVC mode gains higher energy value and becomes less-sensitive to the increase of the Reynolds number as the confinement ratio decreases. This is linked to the asymmetry mode shapes, and energy content linearity between the axial and radial components associated with the single-helix PVC mode.