Swirling flow induced by jets and plumes

The far-field interactions of the slow flow induced by the entrainment of jets and plumes with the surrounding geometry may induce swirling motion. When the initial size of the jet or plume a is much smaller than the characteristic radial distance r_∞ at which the swirl is generated, the evolution of the flow in the presence of bounding walls leads to a selfsimilar description with weak swirling motion, valid at intermediate radial distances a ≪ r ≪ r_∞. It is found that the selfsimilar solution for the circulation Γ is of the second kind, with the exponent λ in the radial decay rate Γ ∝ (r/r_∞)^λ obtained as an eigenvalue. The resulting velocity distributions can find application in mathematical formulations of jet and plume problems involving interactions with ambient swirl, including dust devils and fire whirls.