We report a comprehensive set of direct numerical simulation benchmarks of bypass transition in the narrow sense with inlet freestream turbulent intensity levels $0.75\%$, $1.5\%$, $2.25\%$, $3.0\%$, and $6.0\%$, respectively. Detailed descriptions of length scales and the rate of viscous dissipation are provided. We address two key physical questions. First, how do the decay rates and length scales of freestream turbulence over a transitional and turbulent boundary layer compare to those in spatially developing isotropic turbulence without the wall? Second, what bypass mechanisms drive turbulent spot inception at the intermediate range of freestream turbulence intensity level? We find that the boundary-layer freestream turbulence decay and length scales evolve similarly to their spatially developing isotropic turbulence flow without the wall counterparts. We also present evidence of the coexistence of two turbulent spot inception mechanisms at the inlet FST level $2.25\%$: the long low-speed streak primary and secondary instabilities (only in lower inlet FST levels) and the self-amplifying process of oblique vortex filaments interacting with a Δ-shaped low-speed patch underneath (prevailing only in higher inlet FST levels).

Close

PrevNext

View figure in article

• Boundary layer receptivity, stability & separation
• Isotropic turbulence
• Kelvin-Helmholtz instability
• Structure & turbulence of boundary layers
• Transition to turbulence
• Turbulence
• Turbulence simulations
• Turbulent boundary layers
• Vortex interactions
• Direct numerical simulations