Laser Diagnostics in Two Phase Flows (English shop)

Sascha Krüger’s dissertation “Laser Diagnostics in Two Phase Flows” investigates the development and application of non-intrusive laser-based measurement techniques for characterizing gas-liquid two-phase flows. The research focuses on simultaneously determining gas and droplet velocities, acceleration behavior, and evaporation processes in complex spray systems. An optical flow algorithm is adapted to extract velocity fields from image sequences and implemented in the Gaseous Imaging Velocimetry (GIV) technique. The approach is validated against established Particle Image Velocimetry (PIV) measurements and applied to spray flows and reacting gaseous flows. Particular attention is given to Laser Flow Tagging Velocimetry (LFT), enabling velocity measurements of both gas and liquid phases in dense sprays. Stereoscopic extensions allow three-dimensional velocity vectors to be reconstructed within a measurement plane, even under turbulent flow conditions. Experiments involving gasoline direct-injection sprays examine droplet motion, acceleration, and interactions between sprays and nearby walls. The dissertation also develops high-precision methods for measuring microdroplet sizes and evaporation rates, supported by a monodisperse aerosol generator designed for wind tunnel experiments. Laser-induced fluorescence techniques are additionally considered for determining vapor concentrations surrounding evaporating droplets. The resulting experimental data provide a foundation for improving and validating numerical models of multiphase flows, spray dynamics, and evaporation phenomena.