The vortical structure of the turbulent, confined, coaxial geometry with a central lobe forced mixer have been determined by measurements using a two-component fibre-optic laser-Doppler anemometer at a Reynolds number of 5.1 × 104 (based on the baseline circular nozzle diameter, Di = 30 mm, and bulk mean velocity, U?" of the two streams at 1.7 m/s). Ratios of the annular mean to the core mean velocity (X) were kept at 0.4, 1.1 and 2.0 respectively. Results showed that the mixing processes were greatly enhanced by the formation and interactions of the normal and streamwise vorticity. In particular, the deformation and the subsequent stretching of the normal vortices shed at the nozzle walls by the streamwise vortices played a crucial role in the mixing processes. The higher speed stream appeared to determine the form of mixing downstream. For all the cases considered, strength of the streamwise vorticity were dissipated within 6D1 from the nozzle exit plane.