Enhancing Spatial Resolution and Signal Intensity of Laser Doppler Velocimetry for Flow Sensing Through Optical Path Optimization

In response to the high spatial resolution and accuracy requirement for non-contact flow velocity sensors in complex flow field measurements, this article explores the impact of laser beam expansion in the laser emission path on the flow velocity sensing performance of the reference beam-type Laser Doppler Velocimeter (LDV), aiming to enhance the measurement capability of the LDV. Through simulation analysis and experimental verification, the study analyzes the effects of beam expansion on the measurement volume, scattered signal intensity, velocity signal intensity, and measurement accuracy of LDV. The results indicate that increasing the expansion factor from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5\times $ </tex-math></inline-formula> to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9\times $ </tex-math></inline-formula> leads to a 60.38% decrease in the LDV measurement volume, a 5.31-fold increase in scattered light intensity, and nearly a doubling of the velocity signal intensity measured by LDV. The reduction in measurement volume effectively improves the spatial resolution of the flow field measurement, and also improves the accuracy of velocity measurement. Additionally, the enhanced scattered light signal improves the LDV’s ability to sense velocity signals from small particles. Smaller particles exhibit better velocity tracking characteristics, making the flow velocity measurement results more accurate. These improvements are of great significance for precise sensing and analysis of complex flow fields and dynamic behaviors.