Optical Velocity Measurement and Fluid Flow Visualization Techniques

Abstract

Numerous fluid flow phenomena intrigue researchers worldwide. Flow visualization usually precedes experimental research and gives insight into flow structures. It can be used to show how the fluid flows around the model, in a jet, in closed systems, in turbomachinery, etc. In numerous cases, geometries are very complex, and some chemical reactions occur, but they are not treated here. Smoke, tufts, paints, sewing thread, smoke, and tuft probes are employed together with illumination systems, like LED lamps or lasers. With the laser development, a new era of fluid flow velocity measurement techniques started. Soon after the laser invention, a laser Doppler velocimetry (LDV) was developed and applied in fluid mechanics. Nonintrusive era of fluid flow investigation has started. Various laser models, from continuum, and diode ones to impulse are widely used. Three-component systems, even five beams probes, are employed today in complex research. In-plane, stereoscopic, multi-plane stereoscopic, time-resolved, micro, holographic, scanning, tomographic, and thermographic particle image velocimetry (PIV) have been used. In this case, besides illumination devices, contemporary applications employ fast cameras nowadays. Research of the turbulent swirling flow in pipe, behind the axial fan impeller, with the help of the LDV and PIV systems, as well as some results on wing tip vortex research in wind tunnel tests, are presented.