The turbulent mixing of axisymmetric jet flows is investigated using large-eddy simulation (LES) and Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD). The flowfield of interest consists of a round jet and a surrounding, coaxial annular jet ejected into a quiescent free stream. This flow situation arises, for example, in the flow of hydrogen and oxygen in rocket combustion systems. In such cases, the jets have significantly different densities, which has been found experimentally to strongly influence the downstream turbulent mixing dynamics. The goal of the present study is to evaluate the capacity of the LES and RANS methodologies to accurately predict jet mixing without the complicating effects of combustion. Simulations were performed for test cases matching an experimental study that has been documented in the open literature. Both air-air and hydrogen-air jet combinations were investigated, yielding density ratios ranging from 1.46 to 0.08. The LES and RANS results were compared to one another and to experimental measurements in terms of centerline decay and radial distribution of mean velocity and concentration. The results highlight the strengths and weaknesses of the two computational approaches for this class of problems.

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