The Structure of Turbulent Flows

Abstract

Figure 22.1 shows four photographs of a turbulent boundary layer. Hydrogen bubble markers were released in small squares (as described in Section 23.4) from a fine wire parallel to the wall and perpendicular to the mean flow. The different pictures were taken with the wire at different distances from the wall, ranging from close to the wall to close to the outer edge of the boundary layer. It is apparent that the flow has considerable ‘structure’: different parts of the boundary layer show marked differences in the dye patterns; in each part certain features can be picked out, e.g. the longitudinal streaks in Fig. 22.1(a) and the large irregular patches into which dye has collected in Fig. 22.1 (b) and (c).