Increasing trade of liquefied natural gas (LNG) imposes stringent requirements for accurate flow rate measurement of this high energy content fluid. To satisfy this demand, a flow meter has been developed by CEASAME Exadebit which is based on velocity measurement behind a contraction nozzle using Laser Doppler Velocimetry technique (LDV). For this instrument, a calibration factor is defined relating the measured velocity to the flow rate. This calibration factor depends on the Reynolds number and it can be sensitive to the velocity profile behind the nozzle outlet and to presence of upstream flow disturbances such as bends, valves, etc. when the meter is installed on-site. In this paper, CFD modelling, using OpenFoam software, was employed to analyse the sensitivity of the calibration factor to flow disturbances for two types of disturbing elements; a U-bend and half-plate orifice. The CFD model was validated by comparison with experimental data for the calibration factor and velocity profiles obtained from preliminary LDV measurements with air. Two measurement setups were considered where the velocity is measured either in one point at the nozzle axis or integrated along a line across the nozzle diameter. The results show that the considered disturbing elements cause deviations in the calibration factor in the order of tenths of percent and that the maximal sensitivity of the line-setup to these disturbances is approximately half of the maximal sensitivity of the point-setup. On the other hand, it was shown that the line-setup is more sensitive to the LDV positioning than the point-setup.

液化天然气 (LNG) 贸易的增加对这种高能量含量流体的准确流量测量提出了严格的要求。为了满足这一需求，CEASAM Exadebit 开发了一种流量计，该流量计基于使用激光多普勒测速技术 (LDV) 对收缩喷嘴后面的速度进行测量。对于该仪器，定义了一个校准系数，将测得的速度与流速相关联。该校准系数取决于雷诺数，并且当仪表安装在现场时，它可能对喷嘴出口后面的速度分布和上游流动扰动（例如弯曲、阀门等）的存在敏感。在本文中，CFD 建模，使用 OpenFoam 软件，用于分析校准因子对两类干扰元素的流动干扰的敏感性；U 形弯曲和半板孔。CFD 模型通过与从空气的初步 LDV 测量获得的校准因子和速度剖面的实验数据进行比较来验证。考虑了两种测量设置，其中速度要么在喷嘴轴上的一个点上测量，要么沿喷嘴直径上的一条线积分。结果表明，所考虑的干扰元素会导致校准因子的偏差达到百分之十的数量级，并且线路设置对这些干扰的最大灵敏度约为点设置最大灵敏度的一半。另一方面，