Laser-pulse interferometry applied to high-pressure fluid flow in micro channels

The miniaturization of hydraulic systems together with ever increasing static and dynamic fluid pressure as is happening in fuel injection systems leads to complex flow effects with very high local and temporal pressure gradients. System optimization for hydraulic efficiency, components durability or spray formation quality needs the understanding of relevant flow properties. Fluid flow simulation models support such understanding, but with the complex nature of flow conditions, they are in need for precise and comprehensive verification and validation data. This work reports on measurement methods and analysis results for local fluid density and pressure measurements under overall stationary, highly turbulent and cavitating flow conditions in planar, optically accessed, model flow experiments. Laser-pulsed interferometry is applied for the measurement of fluid density fields under high spatial (∼3 μm) and temporal (∼5 ns) resolution. Interferometric imaging and image evaluation techniques provide ensemble mean pressure field data, local pressure fluctuation and differential pressure data. This yields information about local flow features such as flow vortex generation frequency, spatial size and shape of vortices and local pressure distribution inside of vortex structures. Features of bubble collapse process and corresponding pressure shock waves have been observed. The analysis method is applied to a forward-facing step and a target flow geometry. Experimental method, evaluation procedures and results are presented in this paper.