The aim of this application of Doppler global velocimetry was to provide three-component, phase-averaged velocity data of the engine exhaust flow with a phase-resolution of 5-10o for direct comparison with numerical simulations, ultimately providing a means of validating numerical simulations used in the industrial design process. The test object chosen for this application was an unfired, externally driven four cylinder, turbo-charged engine driven at 2000 rpm (partial power) and 6000 rpm (maximum power). Phase-averaged DGV measurements were made possible by adding an acousto-optic modulator (Bragg cell) to an existing DGV system that was previously optimized for the measurement of time-averaged velocities. CCD cameras with a high signal-to-noise ratio and low dark current (background signal) allowed for integration times up to one minute thereby obtaining velocity averages of more than 1000 cycles. The DGV measurements were performed at the exit plane of the exhaust manifold for cylinders 3 and 4.
Further details can be found in our paper presented at the 10th Intl. Symp. on Applications of Laser Technique to Fluid Mechanics which is available for download (PDF-Format, 1.2 MB).
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