“Turbulent Spot” Deep Inside the Turbulent Boundary Layer with Exascale Simulation

Abstract eng:
Zero-pressure-gradient flat-plate boundary layer (ZPGFPBL) beneath a continuous flow of freestream nearly-isotropic turbulence (FST) from momentum thickness Reynolds number 80 to 3000 has been computed with direct numerical simulation (DNS) on 4 billion grid points. The thoroughly validated DNS data reveal an intriguing unknown flow physics feature: In the fully turbulent region after transition, the near-wall layer (log-layer and below) is populated with hairpin-packed turbulent “turbulent spot”. Although less distinct due to their existing in a chaotic turbulent environment, these turbulent “turbulent spots” nevertheless bear certain similarities to the commonly known transitional turbulent spots which are also packed with hairpin vortices. In the outer forty percent of the boundary layer, the flow is populated by large-scale hairpin forest. Both features persist until the end of the computational domain at momentum thickness Reynolds number 3000.

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