Domain size effect on a temporally evolving stably stratified shear layer

Direct numerical simulations are performed for a temporally evolving, stably stratified shear layer with various computational domain sizes in the spanwise direction. Strong mean shear acting on turbulence, generated by Kelvin-Helmholtz instability, results in increasingly anisotropic velocity fluctuations over time. The streamwise length scale becomes much larger than those in the spanwise and vertical directions, which is attributed to the presence of elongated large-scale structures (ELSS). ELSS form only when the streamwise computational domain is sufficiently large, and they exhibit meandering behavior in the spanwise direction.

When the spanwise width is varied, the transition process from Kelvin-Helmholtz instability to turbulence is altered, and ELSS are not observed in the smallest domain. In cases where the spanwise width is restricted and does not provide sufficient room for meandering, ELSS appear as streamwise-elongated structures without significant lateral wandering. The spectral and two-point correlation analyses indicate that the statistical behavior of the flow is determined more decisively by the presence of multiple ELSS in the spanwise direction, whereas the meandering of ELSS primarily affects the flow structure.