Global Density Effects on the Self-Preservation Behavior of Turbulent Free Jets.
Global Density Effects on the Self-Preservation Behavior
of Turbulent Free Jets.
Richards, C. D.; Pitts, W. M.
Journal of Fluid Mechanics, Vol. 254, 417-435, 1993.
density effects; turbulent jets; flow fields; turbulent
An experimental investigation was designed to test the
hypothesis that all axisymmetric turbulent free jets
become asymptotically independent of the source
conditions and may be described by classical similarity
analysis. Effects of initial conditions were studied by
varying jet exit boundary conditions and the global
density ratio. The exit velocity profile and turbulence
level was changed by using both pipe and nozzle flow
hardware. Initial density differences were imposed by
using three gases: helium, methane, and propane. The
scalar field (concentration) in the momentum-dominated
regime of the far field (10 to 60 jet exit diameters
downstream) of turbulent free jets was characterized
using Rayleigh light scattering as the diagnostic. The
results show that regardless of the initial conditions
axisymmetric turbulent free jets decay at the same rate,
spread at the same angle, and both the mean and r.m.s.
values collapse in a form consistent with full
self-preservation. The means and fluctuations follow a
law of full self-preservation in which two virtual
origins must be specified. The two displacements are
required to account for the effects of a finite source
of momentum and different development of the velocity
and mass distributions in the near fields of the jets.
The memory of the jet is embodied in these two virtual