Journal of Fluid Mechanics

Density fluctuation correlations in free turbulent binary mixing

P.  Chassaing a1, G.  Harran a2 and L.  Joly a3
a1 Institut National Polytechnique, ENSEEIHT, 2 rue Camichel, 31000 Toulouse, France.
a2 Institut de Mécanique des Fluides, avenue du Professeur C. Soula, 31400 Toulouse, France.
a3 ENSICA, 49 avenue L. Blum 31056 Toulouse, France.

Article author query
chassaing p   [Google Scholar] 
harran g   [Google Scholar] 
joly l   [Google Scholar] 


This paper is devoted to the analysis of the turbulent mass flux and, more generally, of the density fluctuation correlation (d.f.c.) effects in variable-density fluid motion. The situation is restricted to the free turbulent binary mixing of an inhomogeneous round jet discharging into a quiescent atmosphere. Based on conventional (Reynolds) averaging, a ternary regrouping of the correlations occurring in the statistical averaging of the open equations is first introduced. Then an exact algebraic relationship between the d.f.c. terms and the second-order moments is demonstrated. Some consequences of this result on the global behaviour of variable-density jets are analytically discussed. The effects of the d.f.c. terms are shown to give a qualitative explanation of the influence of the ratio of the densities of the inlet jet and ambient fluid on the centerline decay rates of mean velocity and mass fraction, the entrainment rate and the restructuring of the jet. Finally, the sensitivity of second-order modelling to the d.f.c. terms is illustrated and it is suggested that such terms should be considered as independent variables in the closing procedure.

(Published Online April 26 2006)
(Received July 21 1993)
(Revised May 19 1994)