Monochromatic flow profile sensor with time division multiplexing and calibration models für fluids

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Shear layer flows are of outstanding importance in basic research as well as in industrial applications with examples covering the range from turbulence research to aerodynamics or heat flow measurement. For their determination, high spatial resolutions are required in general. Furthermore, reflections from walls can occur at laser-based methods, which might result in systematic measurement errors. The aim of highly spatially resolved flow profile measurements even at large working distances can be achieved by means of the laser Doppler velocity profile sensor, whose properties have been investigated within a research project funded by German Research Foundation. The sensor is based on the utilization of two superposed interference fringe systems distorted by defined wavefront curvature. Using a two-channel measurement, which so far has been generated by means of two laser wavelengths, the position of particles carried with the flow can be determined with micrometer spatial resolution. Measurements in the proximity of walls can be performed using fluorescent scattering particles, however, a sensor employing only one laser wavelength is necessary to this end. Hence, a monochromatic profile sensor based on time division multiplexing is to be investigated and realized until a demonstrator within this transfer project. Beside measurements in wall proximity, one key aspect of this project will be the development of a model for sensor calibration. Since the geometries of the interference fringe systems depends on the refractive index of the surrounding medium, any change of the working fluid would demand a new calibration. Especially in liquids, a calibration based on rotating velocity references is impractical, so that a deep penetration of the market cannot be expected. This problem will be solved by developing a calibration model.