The Laser-2-Focus (L2F) technique is applied in the non-intrusive measurement of flow velocity vectors in gases and liquids. Here the velocity of extremely small particles is recorded which are usually present in all technical flows or may be added if required. The scattering light which the particles emit when irradiated by a light source is used in this measurement. The required particles are in the size range of the light wave length and follow the flow even at high acceleration so that correlation between particles and flow velocity is assured. In the measuring volume of the L2F device, which is typically located 500mm from the optic system, two highly focussed parallel beams are projected which function as a light barrier. One of the particles conveyed by the flow which passes through the two beams emits two consecutive light signals and the time interval serves as a value in the determination of the particle velocity.
The applicability of the L2F technique especially in velocity measurements has been demonstrated in several individual cases, e.g. for wind velocity measurements, for investigations in heat exchangers, in steam flow, in water pumps, in plasma flow, in diesel motors and in wind tunnels. Most applications however deal with measurements in turbomachinery.
Data resulting from L2F measurements (three main velocity components, turbulence intensities, Reynolds shear stress and velocity pdf) have contributed greatly to the understanding of flow in turbomachinery. This holds especially for the flow within the rotating components (e.g. turbine rotors), which generally cannot be investigated at all using conventional measuring methods. Comparisons between laser anemometer data and theoretical calculations have resulted in improved mathematical models and design procedures