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ISSN オンライン: 2642-0554

STATISTICS OF THE TURBULENT/NON-TURBULENT INTERFACE IN A SPATIALLY EVOLVING MIXING LAYER

Antonio Attili
Clean Combustion Research Center King Abdullah University of Science and Technology Kingdom of Saudi Arabia

Juan C. Cristancho
Clean Combustion Research Center King Abdullah University of Science and Technology Kingdom of Saudi Arabia

Fabrizio Bisetti
Clean Combustion Research Center King Abdullah University of Science and Technology Kingdom of Saudi Arabia

要約

The thin interface separating the inner turbulent region from the outer irrotational fluid is analyzed in a direct numerical simulation of a spatially developing turbulent mixing layer. A vorticity threshold is defined to detect the interface separating the turbulent from the non-turbulent regions of the flow and to calculate statistics conditioned on the distance from this interface. The statistics of the position of the two interfaces in the mixing layer, i.e., on the low- and high-speed sides, are characterized by a Gaussian distribution and evolve in the streamwise direction coherently with the self-similar behavior of the flow. A strong vorticity jump is observed at the interfaces, in agreement with the results for other free shear flows, such as turbulent jets and wakes. Far from the interfaces, the conditional vorticity recovers the value observed for the classical turbulent statistics in the middle of the layer. The thickness of the interfaces are found to be of the order of the Taylor's microscale, similarly to other shear flows. Finally, the local velocity of the interfaces with respect to the flow is of the order of the Kolmogorov velocity, confirming that entrainment is governed by the dynamics of the smallest scales.