Effect of Stratification on Near-Wall Streaks

We study the effect of stratification on near-wall streaks, defined as regions of slowly moving fluid elongated in the direction of the mean flow, in a turbulent boundary layer. Stable stratification suppresses vertical transport of momentum, which affects the number, size, and location of near-wall streaks. Analyzing the effect of stratification on streaks offers insight into the overall dynamics. Streaks are identified using direct numerical simulation data under the Boussinesq approximation at low Reynolds number in neutrally and stably stratified cases, following the method of Bae & Lee, PRF, 2021. Streaks are classified according to their relative distance from the wall and size. The distribution of streaks between these categories is analyzed, and volume, aspect ratio, meandering, and other spatial characteristics are compared between the neutral and stratified cases. We investigate how streaks and the dominant production mechanism change with Richardson number.