ACQUISITION AND ANALYSIS OF COHERENT STRUCTURES IN TURBULENT RAYLEIGH-BÉNARD CONVECTION USING TEMPERATURE SENSITIVE PAINT

Kurzfassung

In order to study temperature fields at the boundaries of turbulent convective flows, we adopted and applied the temperature sensitive paint (TSP) technique to a Rayleigh-Bénard experiment with quadratic vertical cross section and variable vertical aspect ratio. Hereto, a thin layer of TSP, consisting of a luminescent dye embedded in a polyurethane matrix, was applied to a 1.1 mm thick, water-cooled borosilicate cooling plate. We used water as working fluid (Prandtl number Pr = 7.0) and illuminated the TSP with four UV-LEDs (λab ≈ 395 nm) from above and under varying angles. The frequency-shifted, luminescent light of the TSP, whose intensity depends upon the temperature, was detected using a CCD camera, allowing us to observe the thermal finger prints of the turbulent thermal structures near the top wall. By proper calibration of the luminescence signal, spatially and temporally resolved temperature fields of the TSP layer were measured at aspect ratios between Γ = 4 and Γ = 32 and Rayleigh-numbers in the range 2.6 × 10^4 ≤ Ra ≤ 1.5 × 10^7. The acquired data allows us to observe and study the transition between different coherent large-scale structures and to evaluate the spatio-temporal statistics of the underlying temperature fields in the boundary layer. This work was funded by the priority program Turbulent Superstructures (SPP 1881) of the Deutsche Forschungsgemeinschaft (DFG) - 429432497.