Automatic spatial characterization of low-speed streaks from thermal images

A deterministic model for the sublayer streaks in turbulent boundary layers for application to flow control

“…For example, Klewicki et al (1995) obtained an average spacing of 93n/U t at R q Z1.5!10 6 (where R q is the Reynolds number based on boundary-layer momentum thickness), which is within the range of experimental values at very much lower Reynolds numbers. The range in values of l C opt found in figure 6 lies within the range of experimental values for average streak spacing reported by Zacksenhouse et al (2001). The variation of optimal streak strength with Reynolds number is also plotted in figure 6.…”

“…Figure 4 shows how the strength of the streaks varies with l C Z2p/b C (b C h bn/(U t d à )) for the boundary layer developing under zero pressure gradient, as well as for those in favourable and adverse pressure gradients. It can be seen that the optimum value is approximately 78, which is within the range of mean streak spacing seen in experiments (see the review of previous experimental studies given by Zacksenhouse et al 2001). The precise optimum streak spacing found in our simulations depends also on the values of the source parameters a and b.…”

Large Eddy Simulation of the Flow around one Single-Stacked Container Freight Wagon

“…The mean spanwise spacing between low-speed streaks is reported from experimental studies to be around 100-120 λ + and the spanwise width of the low-speed streaks is reported to range from 33-100 λ + . The mean length of the streaks are reported to be around 1000 λ + but much shorter and longer lengths can be observed ( [22,23,24]. In Fig.…”

“…In Fig. 11 low and high speed streaky structures in the viscous layer are shown from the experimental study [24]. For a comprehensive review and description of streaks and other coherent flow structures occuring in the turbulent boundary layer and the present understanding of them we refer the reader to [25].…”

“…1800λ + Figure 7: Thermal image from the experimental study of spatial characteristics of near-wall streaks in boundary layers. Picture is taken from [24]. Dark regions corresponds to high-velocity regions and bright regions are low-velocity regions.…”