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Turbulent mixing at a stable density interface : the variation of the buoyancy flux–gradient relation

By Estelle Marie Chantal Guyez, J. -B. Flor and E. J. Hopfinger

Abstract

Experiments conducted on mixing across a stable density interface in a turbulent Taylor–Couette flow show, for the first time, experimental evidence of an increase in mixing efficiency at large Richardson numbers. With increasing buoyancy gradient the buoyancy flux first passes a maximum, then decreases and at large values of the buoyancy gradient the flux increases again. Thus, the curve of buoyancy flux versus buoyancy gradient tends to be N-shaped (rather than simply bell shaped), a behaviour suggested by the model of Balmforth et al. (J. Fluid Mech. vol. 428, 1998, p. 349). The increase in mixing efficiency at large Richardson numbers is attributed to a scale separation of the eddies active in mixing at the interface; when the buoyancy gradient is large mean kinetic energy is injected at scales much smaller than the eddy size fixed by the gap width, thus decreasing the eddy turnover time. Observations show that there is no noticeable change in interface thickness when the mixing efficiency increases; it is the mixing mechanism that changes. The curves of buoyancy flux versus buoyancy gradient also show a large variability for identical experimental conditions. These variations occur at time scales one to two orders of magnitude larger than the eddy turnover time scale

Topics: QA
Publisher: Cambridge University Press
Year: 2007
OAI identifier: oai:wrap.warwick.ac.uk:664

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Citations

  1. (1993). A mathematical model of turbulent heat and mass transfert in stably stratified shear flow. doi
  2. (2000). Advanced optimization of correlation imaging velocimetry algorithms. doi
  3. (1973). Buoyancy Effects in Fluids. doi
  4. (1998). Dynamics of interfaces and layers in a stratified turbulent fluid. doi
  5. (1997). Experimental study of circular Couette flow in a stratified fluid. Fluid Dyn. doi
  6. (1991). F e r n a n d o doi
  7. (1988). H a n n o u n ,I .A .&L i s t doi
  8. (1997). Low cost, high resolution dpiv for measurement of turbulent fluid flow. doi
  9. (1997). Mixed layer deepening due to Langmuir circulation. doi
  10. (1979). Mixing in stratified fluids. doi
  11. (1986). On mixing across an interface in stably stratified fluid. doi
  12. (1969). On the penetration of a turbulent layer into stratified fluid. doi
  13. (1995). Role of Langmuir circulation in the deepening of the ocean surface mixed layer. doi
  14. (2000). Stability and bifurcations in stratified Taylor– Couette flow. doi
  15. (1977). The generation of salinity finestructure by vertical diffusion. doi
  16. (1968). The influence of molecular diffusivity on turbulent entrainment across a density interface. doi
  17. (1978). Turbulence and mixing in stably stratified waters. doi
  18. (1971). Turbulence in a strongly stratified fluid- is it unstable? Deep Sea Res. doi
  19. (1994). Turbulent mixing in stratified fluids: layer formation and energetics. doi

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