Structure of turbulence in the marine atmospheric surface layer
Boppe, Ravi Shankar
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Turbulence research in the laboratory has confirmed the existence of quasi-coherent structures amidst the chaos of a turbulent boundary layer. It has been observed that a quasi-periodic phenomena called "bursting" accounts for a major contribution to the turbulent Reynolds stress and the production of turbulent kinetic energy. Bursting is the term used for a sequence of events, where a low-speed streak of fluid from the near wall region lifts a.way from the wall, slowly at first, and then rapidly moves away from the wall as it convects downstream where it becomes unstable and breaks up violently upon interaction with the outer flow. This ejection of low speed fluid into the mean flow is responsible for locally high values of turbulent kinetic energy. Although a great deal is known about these structures in laboratory flows, little has been done to investigate if such structures are universal in turbulent flows, i.e., their existence in large Reynolds number flows such as the turbulent air flow over the ocean. It would seem, intuitively, that such structures, if present in the marine atmospheric boundary layer, would playa major role in the transfer of momentum, mass and heat across the air-sea interface. It is speculated that these motions may also be associated with large scale organized motions in wall bounded turbulent shear flows. The effort aimed at elucidating the physics underlying such structures would be invaluable in contributing to our understanding of the air-sea flux mechanism.
- Doctoral Dissertations