Uncertainty evaluation for velocity-area methods

Velocity-area methods are used for flow rate calculation in various industries. Applied within a fully turbulent flow regime, modest uncertainties can be expected. If the flow profile cannot be described as “log-like”, the recommended measurement positions and integration techniques exhibit larger errors. To reduce these errors, an adapted measurement scheme is proposed. The velocity field inside a Venturi contour is simulated using computational fluid dynamics and validated using laser Doppler anemometry. An analytical formulation for the Reynolds number dependence of the profile is derived. By assuming an analytical velocity profile, an uncertainty evaluation for the flow rate calculation is performed according to the “Guide to the expression of uncertainty in measurement”. The overall uncertainty of the flow rate inside the Venturi contour is determined to be 0.5% compared to ≈0.67% for a fully developed turbulent flow.