Burst Digital Correlator as LDV Signal Processor

Abstract

Current LDV techniques have been employed in undertaking the challenge to the understand complex physical phenomena of flow velocity and turbulence characteristics such as those found in engines, turbomachinery, near wall, and combustion equipment. Especially, it is very important to distinguish turbulence and fluctuation in order to understand the cyclic variation. An optical fiber linked LDV (FLDV) has been developed to flows to which could hardly be made y the conventional LDV access, but the performance of the FLDV has not been enough for in- cylinder flow. The LDV system should be optimized not only for optics but also for signal processing. In shear flow regions such as step-back flow and recirculating flow, there are very large velocity gradient regions where high spatial resolution of the measurement volume is required. When the size of the measurement volume decreases, the fringe spacing has to be small to ensure a minimum fringe number, which induces an increase in the detected frequency. Furthermore, having a large memory with a high data rate is also required to analyze the in- cylinder flows and oscillating flow. In order to overcome these problems and for further LDV applications, the LDV processor should be developed, whose performance is characterized by wide bandwidth, low SN ratio, high data rate, large memory, and real time monitoring.