Abstract
Orifice meters are used for the measurement of flow rate, particularly in the natural gas industry. They are relatively simple and inexpensive devices; the flow rate is calculated by observing the pressure drop across an orifice plate. Uncertainty of metering accuracy has resulted in an estimated tens of millions of dollars of annual mischarges for gas companies. This has led to basic research on methods to improve orifice meter accuracy. Those investigations underline the importance of the upstream velocity profile effects upon the orifice plate discharge coefficients Cd- Changes in q are undesirable because they cause inaccuracies in flow measurement. This study was undertaken to determine the effect of the upstream velocity profile upon the flow field inside a standard orifice flowmeter. A 3-D LDV (Laser Doppler Velocimeter) was used to obtain detailed velocity and turbulence measurements for a flow of air in an orifice meter (P=0.5) at a Reynolds number of 91,100 with three different inlet velocity profiles. Analysis of the correlated, instantaneous velocities in three dimensions enabled calculation of the mean velocity components, the complete Reynolds stress tensor for compressible flow: [], the triple correlations, the rate of turbulence production, vorticity, and turbulent kinetic energy. In addition, particularities of such a turbulent flow were determined: the point of reattachment, the downstream primary recirculation zone and the upstream recirculation zone, the axial location of maximum velocity (vena contracta).
Robic, Bernard Francois (1995). A 3D laser doppler velocimetry study of the upstream velocity profile effects upon the flow field inside an orifice flowmeter. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -R624.