Numerical Simulation of the Formation and Motion of Turbulent Vortex Clouds (Puffs)

The results of numerical simulation of the formation and motion of turbulent vortex clouds (puffs) resulting from the blowing of pulsed jets with various initial velocities and durations are given. A model of axisymmetric turbulent flow described by the time-dependent Reynolds equations is adopted. It is shown that, regardless of the initial conditions, a puff which has the shape similar to a sphere develops after the same dimensionless time interval from the instant of jet outflow. In the rest of the space the vortex-induced flow is close to a potential flow. It is found that in the vortices the velocity profiles in the axial and transverse directions are close to self-similar profiles and similar each other for various conditions of outflow of pulsed jets. The time dependences of the geometric and kinematic characteristics of puffs, namely, the location of the cloud center (points with the maximum velocity) and the radius of a sphere equivalent in volume to the puff, as well as the maximum and mean velocities, are given and analyzed. For the jet outflow conditions considered, the characteristics of puffs turn out to be similar.