A New Look at the Near-Wall Turbulence Structure

An experiment was carried out in the BMT environmental wind tunnel (4.8m × 2.4m × 15m) in order to study the near-wall structure of the turbulent boundary layer, particular attention being given to the dynamics of the “near-wall bursts” [1]. Conditional samping of the wall-shear stress fluctuations was extensively used along with a simultaneous application of flow visualisation using a streak-smoke wire and a sheet of laser light. The results suggested that a “near-wall burst” was taking place between a pair of smoke tubes, which was interpreted as a pair of stretched legs of neighbouring hairpin loops. The spanwise spacing of the “near-wall bursts” determined from a conditional space correlation of skin-friction signals was found to be a function of the threshold value used in burst detection.