Observations and LDA measurements of confined turbulent vortex flow

A series of LDA measurements and visual observations of confined turbulent vortex flow are described. The experiments were performed with water as the fluid medium in a vortex tube of length-to-diameter ratio L/D = 3.8 for a range of exit diameters De between De/D = 1 and 0.18. The experiments reveal a remarkable change in the vortex structure as De is reduced: from a thick core with an axial-velocity defect in the centre, and even reversed flow, to a thin annular jet-like core with a peak axial velocity more than an order of magnitude greater than the average value and again a central velocity deficit. The corresponding swirl profiles are not remarkable and are well-represented under all conditions by the solution of Burgers (1948), albeit with a velocity maximum which is strongly dependent upon De.