High spatially resolved turbulent boundary layer measurements by fiber-optic heterodyne-velocity-profile-sensor

A fiber-optic LDA-velocity-profile-sensor was realized for high spatially resolved velocity measurements in turbulent boundary layers. The sensor can resolve the position of a tracer particle passing through the measurement volume along optical axis. Therefore velocity measurement with a high spatial resolution is possible compared with a conventional LDA (laser Doppler anemometry). The measurement accuracy of the sensor was investigated with respect to the velocity measurement and the spatial resolution. The sensor successfully resolved the velocity distribution in a laminar boundary layer on a flat plate. Then it was applied to turbulent boundary layers in a fully developed duct flow. The measured results showed fairly good agreement with a direct numerical-simulation result. However, the improvements are necessary for obtaining reliable statistics.