Modernization of DLR's L2F System Featuring an Air-Cooled Optical Probe Design

A new optical probe for the well-established Laser-2-Focus (L2F) system at the German Aerospace Center (DLR) has been designed for velocity measurements in the demanding conditions of the DLR Next Generation Turbine Test Facility (NG-Turb). The new design enables L2F measurements in the vicinity of the turbine's first stage rotor while traversing radially and circumferentially through the test rigs annular space. The optical probe was tested at a free jet flow and featured adequate signal rates and amplitudes. Moreover, the implementation of diode lasers, silicon-based light detectors, and FPGA-based electronics are evaluated. The technological progress in the development of these devices open up new opportunities for enhancing, miniaturizing and simplifying the L2F system's architecture. Accordingly, a new four-color laser system was successfully implemented in the existing L2F system at DLR. Currently, a compact FPGA-based time-to-digital-converter (TDC) is tested and a new software to control the data acquisition is under development. Besides, a supplementary post-processing data evaluation routine enables a more flexible data analysis. The use of silicon photomultipliers (SiPMs) as a replacement of the old photomultipliers (PMTs) will be tested in the near future.