Entrainment and the structure of turbulent flow

摘要: Although the entrainment of non-turbulent fluid into a turbulent flow occurs across sharply defined boundaries, its rate is not determined solely by motion adjacent to interface but depends on overall properties flow, in particular, those that control energy balance. In first place, attention directed many observations which show shear flows has structure closely resembling produced rapid, finite, plane shearing initially isotropic turbulence. The basic reasons for similarity are stability and permanence eddies finite distortions undergone parcels free flows. Next, existence eddy condition balance used account variation rates within groups broadly similar flows, particular mixing layers between streams different velocities wall jets curved surfaces. For some satisfy ordinary conditions self-preserving development, no consistent with development possible. Examples axisymmetric, small-deficit wake distorted wake. Finally, implications an controlled general discussed. It concluded relatively rapid active instability interface, present constant-pressure boundary layer whose slow from ‘passive’ distortion bounding surface main motion. Available tend support this conclusion.