Average Time between Bursts in a Favorable pressure Gradient.

Abstract

Effects of a favorable pressure gradient on the average time between bursts were studied by two different methods : the modified U-level method, and a proposed detection scheme that applies the U-level method to ejections and sweeps. Experiments were carried out in a boundary layer along a flat wall of two-dimensional asymmetric contraction. The results of experiments show that the average time between bursts scaled with inner variables increases with a decrement of the pressure gradient parameter Δp, and the ratio of the Eulerian micro-time scale to the average time between bursts gives a constant value of 0.1 at Y+=15. The proposed method also indicates that bursts still remain throughout the reverse transition process from a turbulent boundary layer to a laminar one.