Computational Fluid Dynamics was used to model spatially developing, initially laminar, gas jets issuing from nozzles of regular and irregular cross-section, using the Large Eddy Simulation (LES) technique. Nozzles were based on bluff jets used in tangentially fired lignite-burning furnaces. Validation of the LES based model was achieved by comparing predicted jet entrainment rates with published experimental and numerical data. Large-scale coherent turbulent structures including ring and braid vortices and other stream wise structures are predicted by the LES model. The shape of the ring vortices formed was found to directly relate to the nozzle geometry. Size and proximity of discontinuities in the vortex rings were observed to determine how strongly a vortex ring deforms, furthermore discontinuities in the ring curvature were found to alter the number of stream wise structures formed. Jets with only a single pair of braid vortices per side were predicted to spread along their axes while those with multiple braids spread more uniformly.