Turbulent fluid interfaces with applications to mixing and aero-optics

The behavior of turbulent flows is investigated using a spatial analysis of fluid interfaces. Understanding turbulent flow phenomena is highly sought after for engineering applications in which the performance may be governed by the behavior of high-velocity and/or low-viscosity large-scale flows. Turbulence-generated interfaces; which consist of isosurfaces associated with a particular flow or fluid parameter, provide a useful means to probe the engineering system of interest by using multi-dimensional image data. Physical-modeling methodologies and flow-imaging experiments are presented with emphasis on turbulent interfaces encountered in large-Reynolds-number flows. The present approach is useful in mixing and aero-optics applications and basic phenomena sensitive to the behavior of irregular interfaces.; Turbulent mixing and the dynamics of interfaces are examined with experiments in liquid-phase turbulent jets in the Octagonal-Tank Flow Facility. Concentration-field measurements are recorded to study the outer interfaces, i.e. the interfaces between mixed fluid and pure fluid, as well as scalar-threshold effects. A database is created of whole-field ∼ 1,0003 three-dimensional space-time interfacial measurements above the mixing transition, at Re ∼ 20,000 and Sc ∼ 2,000, using laser-induced fluorescence of disodium fluorescein in water. The outer interfaces are found to be dynamically confined near the unsteady large-scale flow boundaries. This observation is utilized to develop a new outer-fluid-interface method that quantifies the dominant contributions to the mixed-fluid volume fraction, or mixing efficiency, with robustness to resolution effects.; Refractive interfaces in aero-optics are investigated experimentally using a new Variable-Pressure Aero-Optics Flow Facility that was designed and built as part of this work. Large test-section size, fast gas velocities, and elevated test-section pressures enable experiments in gas-phase separated shear layers at large Reynolds numbers (Re ∼ 10 6) with compressibility effects (M ∼ 1.0). Simultaneous flow and beam imaging is performed to correlate the instantaneous structure of the refractive interfaces to the optical-wavefront aberrations. Laser-induced fluorescence of acetone vapor in air enables the flow imaging and a Shack-Hartmann camera enables measurements of the optical wavefront aberrations. An interfacial-fluid-thickness approach is developed for physically modeling the optical path difference whereby the high-gradient refractive interfaces are found to dominate the large-scale aero-optical interactions.