Turbulent vortex pairs in neutral surroundings

Experiments were conducted in neutral surroundings on turbulent vortex pairs produced with various initial conditions. A pair was observed to spread linearly along the direction of motion: This is expressed as b=0.26z, where b is one half its maximum width and z is the elevation of its leading extremity. The advance of the pair was found to follow Z/b0=2.3(Tw0/b0)1/3, where Z and T are elevation and time, respectively, with respect to the virtual origin; and b0 and w0 are the initial size and velocity of the pair. These results appear to indicate that the motion of the pair follows the similarity solution and relates only to the initial momentum and the entrainment coefficient, regardless of the conditions of its generation. An additional experiment was conducted with polymer solutions to illustrate the influence of turbulent mixing inside the pair on its spreading behavior.