Variable density mixing in turbulent jets with coflow
Two sets of experiments are performed to study variable-density effects in turbulent round jets with co flow at density ratios, s = 4.2 and s = 1.2. 10,000 instantaneous realisations of simultaneous 2-D PIV and PLIF at three axial locations in the momentumdominated region of the jet allow us to calculate the full t.k.e. budgets, providing insights into the mechanisms of density fluctuation correlations both axially and radially in a non- Boussinesq flow. The strongest variable-density effects are observed within the velocity half-width of the jet, r~u1/2 . Variable density effects decrease the Reynolds stresses via increased turbulent mass flux in the heavy jet, as shown by previous jet centreline measurements. Radial pro les of turbulent flux show that in the lighter jet t.k.e. is moving away from the centreline, while in the heavy jet it is being transported both inwards towards the centreline and radially outwards. Negative t.k.e. production is observed in the heavy jet, and we demonstrate that this is caused by both reduced gradient stretching in the axial direction and increased turbulent mass fluxes. Large differences in advection are also observed between the two jets. The air jet has higher total advection caused by strong axial components, while density fluctuations in the heavy jet reduce the axial advection signi cantly. The budget mechanisms in the non-Boussinesq regime are best understood using effective density and velocity half-width, ρeff ¯u3 1,CL/r~u1/2,eff , a modi cation of previous scaling.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE National Nuclear Security Administration (NNSA), Office of Defense Programs (DP)
- Grant/Contract Number:
- AC52-06NA25396
- OSTI ID:
- 1374317
- Report Number(s):
- LA-UR-16-24522
- Journal Information:
- Journal of Fluid Mechanics, Vol. 825; ISSN 0022-1120
- Publisher:
- Cambridge University PressCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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