We experimentally, numerically and theoretically investigate the nonlinear interaction between a cavitation bubble and the interface of two immiscible fluids (oil and water) on multiple time scales. The underwater electric discharge method is utilized to generate a cavitation bubble near or at the interface. Both the bubble dynamics on a short time scale and the interface evolution on a much longer time scale are recorded via high-speed photography. Two mechanisms are found to contribute to the fluid mixing in our system. First, when a bubble is initiated in the oil phase or at the interface, an inertia-dominated high-speed liquid jet generated from the collapsing bubble penetrates the water–oil interface, and consequently transports fine oil droplets into the water. The critical standoff parameter for jet penetration is found to be highly dependent on the density ratio of the two fluids. Furthermore, the pinch-off of an interface jet produced long after the bubble dynamics stage is reckoned as the second mechanism, carrying water droplets into the oil bulk. The dependence of the bubble jetting behaviours and interface jet dynamics on the governing parameters is systematically studied via experiments and boundary integral simulations. Particularly, we quantitatively demonstrate the respective roles of surface tension and viscosity in interface jet dynamics. As for a bubble initiated at the interface, an extended Rayleigh–Plesset model is proposed that well predicts the asymmetric dynamics of the bubble, which accounts for a faster contraction of the bubble top and a downward liquid jet.

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Laser induced fluorescence (LIF) is a non-intrusive optical technique that uses fluorescent dyes to measure whole-field fluid scalars such as temperature, concentration, pH, etc. LIF measurements' accuracy is strongly influenced by the fluorescent dye's behavior under different experimental conditions. In particular, ratiometric LIF thermometry accuracy depends on the correct selection of fluorescent dyes mixtures. Therefore, a thorough characterizations of fluorescent dyes is needed to obtain optimal mixtures and suitable optical configurations for given experimental conditions. This work presents the experimental characterization of fluorescein-27 (FL27) and rhodamine-B (RhB) mixtures to determine suitable aqueous solutions for ratiometric LIF thermometry. The mixtures' fluorescence emission intensity was measured with a spectrofluorometer, and the influence of concentration ratio (C(RhB)/C(FL27)), temperature, excitation wavelength (λ(ext)), and pH were analyzed. The results show that the temperature dependence of FL27 emission intensity changed from a negative to a positive value as the excitation wavelength increased. The temperature sensitivity (4.0% per °C) of RhB and FL27 mixture under 532 nm excitation wavelength was found to be higher than that of the commonly used mixture of RhB and Rh110 (2.0% per °C) at the same excitation wavelength. While the emission intensities of the dyes are sensitive to pH value, the temperature dependence is unaffected. The influence of concentration ratio on temperature sensitivity depends on both the detected bands of the emitted spectrum and the temperature; the concentration ratio should be selected based on the measured temperature scope. A new multicolor method or advanced two color method with high temperature sensitivity (6.0% or 10.0% per °C) is presented. This technique was specially developed to improve whole-field temperature measurements.

The erosion of an axial fan was investigated, both theoretically and experimentally. A computer program was developed to predict particle trajectories and erosion through turbomachines. It also accounts for different boundary conditions and stage interfaces. The governing equations of the particle motion were solved using Runge-Kutta Fehlberg technique in a given flowfield. The tracking of particles and their locations are based on the finite element interpolation method. The methodology was applied to an axial fan with inlet guide vanes (IGV). The flowfield was solved using the TASCflow code. The number of particles seeded upstream of the IGV was determined from experimentally measured profile concentration, with respect to a random distribution of particle sizes. The erosion of the blades and changes to the chord and tip clearances were also measured. The concentration profiles and velocities of the particle were measured with a laser transit anemometer and used as input to the trajectory code. The fan performance was measured before and after sand ingestion to assess the degradation in performance due to the eroded geometry