Laser Doppler Gas Flowmeter with Synchronous Three-Point Measurement

To address the challenges of susceptibility to interference and limited accuracy inherent in conventional gas flow rate measurement methods, this paper proposes and investigates a laser Doppler gas flow rate measurement method based on synchronous three-point velocity measurement. This method simultaneously measures the flow velocities at three characteristic points within the pipeline cross-section, subsequently fits and reconstructs the velocity distribution across the entire profile, and ultimately achieves high-precision flow measurement. The feasibility of selecting the center point, the quarter-width point, and the near-wall point as the three characteristic measurement positions is analyzed through computational fluid dynamics simulations, and the full-profile velocity distribution is fitted accordingly. A three-point synchronous velocity-flow rate measurement system is designed and constructed, employing a transmitting optical path based on the "three beam splitters and two mirrors" scheme and a receiving optical path based on the "multi-lens independent reception" scheme, and experimental validation is conducted. Experimental results demonstrate that the system operates stably with good repeatability. In contrast to the flow calculation method using a single-point Pitot tube combined with an empirical formula, the proposed system, which directly fits the velocity profile and integrates it for flow calculation, effectively avoids the significant model errors caused by using fixed empirical coefficients in non-circular pipe flows, and is inherently more universally applicable in principle. Through comparison with the TSI reference standard (3D LDV), the measurement results of the proposed system are in close agreement with the reference values, with relative errors all below -0.8%. This paper provides an effective solution for high-precision gas flow measurement in square pipelines.