Home > Research > Turbulent Fluid Flows
Quantitative, laser-based imaging of turbulent fluid flows
The majority of fluid flows encountered in engineering systems and in nature are turbulent, yet turbulent flow phenomena continue to resist attempts at a comprehensive understanding. In recent years, planar laser imaging methods have provided noteworthy insight into turbulent flows, particularly regarding their tendency to spatial organization and coherence. Professor Lester Su and his group work to apply advanced laser diagnostic methods, including planar laser-induced fluorescence (PLIF), particle image velocimetry (PIV), and planar laser Rayleigh scattering, to perform truly quantitative, field measurements of mixing and velocity fields in turbulent shear flows.
Professor Su and his students employ these laser imaging methods in a variety of problems of engineering relevance, particularly involving molecular mixing. Figure 1 shows sample Rayleigh scattering images from the mixing of a jet, consisting of a mixture of propane and helium, in ambient air. The propane and helium diffuse at different rates into the surrounding air. This differential diffusion is particularly challenging for computer models of reacting flow systems, which can involve dozens of chemical species, each with its own physical properties. Measurements such as those in Figure 1 quantify the extent of differential diffusion, allowing for the development and assessment of appropriate models for multicomponent mixing.
Figure 2 shows images of jet fluid mole fractions from a helium jet issuing into air. The use of multiple windows provides coverage of the full extent of the developing region of the flow, without compromising spatial resolution. The helium-air jet system has similar density fluctuations to reacting flows, allowing us to isolate the effect of local density differences on the mechanisms of mixing. This will ultimately improve our understanding of turbulent mixing dynamics, and also allow the refinement of methods for simulating mixing and reactions in combustion systems.