An investigation was conducted of two-stream, variable-density, turbulent jet mixing with recirculation confined within an axisymmetric duct that simulated a combustor configuration. The recirculating flow fields in the combustor simulator were the result of coaxial jet mixing between a central, primary air stream with a velocity of about 650 ft/sec and an annular secondary stream of hydrogen with velocities of 13, 23, or 48 ft/sec, depending on the desired test conditions. Experimental measurements are presented of radial distributions of time-averaged axial velocity and hydrogen mass fraction, axial distributions of time-averaged static pressure on the duct wall, axial velocity on the duct centerline, and hydrogen mass fraction on the duct wall and on the duct centerline. A theoretical study of the experimental flows was also conducted using a finite difference numerical solution technique for the calculation of viscous, recirculating flows. Comparison of theory and experiment shows that the predictive technique and the turbulence transport model require further development before accurate prediction of recirculating turbulent flows can be realized.