Application of Liquid Crystal Thermography for the Investigation of the Near-Wall Coherent Structures in a Turbulent Boundary Layer

In this paper, Liquid Crystal Thermography is used to characterise the near-wall coherent structures in a turbulent boundary layer at low Reynolds numbers. The experiments are carried out in a water tunnel at u∞ = 0.12 m/s, in a zero-pressure-gradient turbulent boundary layer at Reθ = 430. A comparison of the frequency response of the liquid crystal coating with that of a constant temperature anemometer shows that the technique is able to capture the flow fluctuations caused by the large turbulent scales in the near-wall region, up to a non-dimensional frequency of f+ ≈ 0.01. This technique is also used to deduce the properties of the streamwise streaks in the viscous sublayer. The results are in agreement with the literature demonstrating the potential of this novel method for studying near-wall turbulence. Finally, the validity of Taylor's hypothesis is also examined using our liquid crystal data.