Streaks instability in adverse pressure gradient wall turbulence

The effect of adverse pressure gradient on wall turbulence is to increase the near wall streaks instability. The breakdown of these streaks generates a strong and sudden production of vortices (in blue) responsible of a second peak of turbulent kinetic energy in the outer part of the turbulent boundary layer. The increase of the streaks instability was demonstrated by a stability analysis on real streaks extracted from a Direct Numerical Simulation of converging-diverging channel flow.