3.1 - Self-Calibrating Doppler Global Velocimeter with Laser Frequency Modulation

In order to optimize the efficiency of compressors and gas turbines, flow measurements are required for investigating important flow phenomena such as the development of vortices. For this purpose, optical measurement tools were developed capturing velocity flow fields non-intrusively. However, those systems are often designed for the use in laboratory under stable environment conditions and require a high expertise. In industrial environments, high temperatures up to several 100 °C can occur e. g. at turbo compressors, which disturbs the measurement and results in significant measurement errors. In order to allow highly resolved flow measurements also in industrial environments and for non-specialists, smart systems using a self-calibration are required. For this reason, a novel self-calibrating technique is presented decreasing automatically the temperature sensitivity. The underlying fundamental idea is to measure the Doppler frequency shift of scattered light obtaining the flow velocity and to correct changes of the slope of the calibration curve implicitly during the measurement by using a frequency modulated laser. This simplifies the application and increases the accuracy. The novel concept is implemented and successfully validated by experiments.