Effects of Upstream Turbulence on Measurement Uncertainty of Flow Rate by Venturi

Venturi has been widely used for measuring flow rate in a variety of engineering applications since pressure loss is relatively small compared with other measuring method. The current study focuses on making detailed estimation of measured uncertainties as the upstream turbulence affects uncertainty levels of the water flows in the closed-loop testing. Upstream turbulences can be controlled by selecting 9 different swirl generators. Measurement uncertainty of flow rate has been estimated by a quantitative uncertainty analysis which is based on the ANSI/ASME PTC 19.1-2005 standard. The best way to reduce error in measuring flow rate was investigated for evaluating its measurement uncertainty. The results of flow rate uncertainty analysis show that the case with systematic error has higher than that without systematic error. Especially the result with systematic error exhibits that the uncertainty of flow rate was gradually increased by upstream turbulence. Uncertainty of flow rate measurement can be mainly affected by differential pressure and discharge coefficient. Flow disturbance can be also reduced by increasing of the upstream straight length of Venturi.