Velocity and Temperature Distributions in Jets with Initially Non-Uniform Profiles

摘要

The development of the velocity and temperature profiles in a turbulent jet with an initially non-uniform velocity profile is studied as an aid to understanding the mixing processes in the above-core plena of nuclear reactors. Jet similarity theory is examined to show what deductions may be made from observed rates of decay and rates of spread of the profiles. Literature data for the 'standard' case of uniform exit profiles show large discrepancies but the best supported results are well reproduced by a finite difference solution of the Navier-Stokes and energy equations with spatially uniform levels of diffusivity for momentum and heat. Measurements on a jet with an initially non-uniform velocity profile indicate that the influence of the initial conditions is rapidly lost and that the self-similar profiles of the uniform exit case appear after approximately 15 diameters. The development can then be adequately predicted from the uniform case and a knowledge of the momentum and heat effluxes alone, since the effective origin appears to be still quite close to the mouth of the jet. Finite-difference calculations have been repeated for this case with various plausible hypotheses about the diffusivity in the initial region of the jet, but without success in reproducing the effective origin exactly. This discrepancy is unlikely to be practically important except in the description of the first few diameters of development. This work is the first step in studies of the interaction of multiple non-uniform jets and of the spread of the temperature profile in a sodium jet. (Atomindex citation 09:386726)