R.E. DeOtte

Comparison of orifice and slotted plate flowmeters

The performance of a standard β = 0.50 orifice flowmeter is compared to the same flowmeter with a slotted orifice plate replacing the standard orifice plate. The slotted orifice plate has the same total open area as the standard plate and consists of three concentric rings, each of which contains several radial slots. The flow upstream of both orifice plates in preconditioned using a concentric pipe device to produce a wide range of axial velocity profiles without swirl. The discharge coefficient of the standard plate varies from the base value by −1% to +6%, while that of the slotted orifice plate varies by only ±0.25%. When swirl is generated upstream of the orifice plates, the discharge coefficients vary by 5% and 2% for the standard and slotted orifice plates, respectively. These data indicate that the slotted orifice flowmeter is superior to the standard orifice flowmeter in maintaining its calibration over a wide range of inlet flow conditions. The slotted orifice plate can be a ‘drop in’ replacement for a standard orifice plate.

Beta ratio, swirl and Reynolds number dependence of wall pressure in orifice flowmeters

Abstract Experimental work has been performed in an effort to gain a better understanding of the flow field inside orifice flowmeters and the pressure field generated on the walls of the pipe and orifice plate. As a part of a larger study, extensive wall pressure measurements have been made on the pipe wall from four pipe diameters upstream of the orifice plate to six pipe diameters downstream, as well as on both the upstream and downstream faces of the orifice plate. These measurements were performed for Reynolds numbers of 54 700; 91 100 and 122 800; for beta ratios of 0.50 and 0.75 with air as the working fluid. An adjustable swirl plate was installed, which was used to impart varying amounts of swirl into the flow upstream of the orifice plate. For each swirl case, Pitot and static pressure probes were used to characterize the upstream flow field while the pipe wall and orifice plate surface pressures were measured.

Numerical Study of the Effects of Upstream Flow Condition Upon Orifice Flow Meter Performance

Recent experimental work has shown that when the mean velocity profile upstream of an orifice plate has a deficit on the centerline and higher velocities at the outer edges of the pipe, the pressure drop across the orifice is greater than if the flow upstream is fully developed. It is proposed that this increase in [Delta]P is directly correlated with the radial distribution of momentum upstream of the orifice plate. In an effort to investigate how the upstream flow condition affects the pressure distribution along the pipe wall and to determine if the hypothesis is correct, Creare.X Inc. s FLUENT numerical analysis program was used to simulate the effects. Two [beta] ratios (0.50 and 0.75) have been considered with various mean velocity inlet profiles. Inlet profiles include the 1/16th, 1/7th, 1/8th, 1/9th and 1/10th power law power law, uniform flow, and two linear distributions. The results indicate that there is a correlation between the second and third-order moments of momentum and the value of the discharge coefficient. This empirical correlation, after being fully verified by experimental data, can be used to estimate the change in the coefficient of discharge given the inlet velocity profile.

3-D laser Doppler anemometry measurements of the axisymmetric flow field near an orifice plate

Abstract Measurements of the axisymmetric velocity field in a standard 50.8 mm (2.0 inch) orifice meter were made using a 3-D laser Doppler anemometer. Calculations were performed using the instantaneous velocity measurements to yield the time-averaged mean velocity components, the products of the fluctuating velocities (which provide the entire Reynolds stress tensor if the density is assumed constant), the correlation coefficients and the turbulence kinetic energy (TKE). For an air flow with a Reynolds number of 54 700, data indicate the point of reattachment, the downstream primary recirculation zone, the downstream secondary recirculation zone and the upstream recirculation zone. It is further evident that the axial location of maximum velocity (the vena contracta) differs from that for minimum wall pressure.

Doppler global velocimetry: problems and pitfalls

Abstract A 1D Doppler global velocimeter (DGV) system was designed and constructed. During the evaluation of this system, inaccuracies were observed which could be attributed to the performance of many individual components. Items requiring evaluation included the performance of video cameras, the transfer lens, the beam splitter, the ALF cell construction, the absorption line filter (ALF) cell charging, and video recording computer boards. Descriptions of the problems and corrections are detailed.

Upstream velocity profile effects on orifice flowmeters

Abstract The effects of upstream velocity profile on the performance of orifice flowmeters were studied. Non-swirling maldistributed axial velocity profiles were obtained using a concentric pipe flow conditioner. Orifice flowmeters with β ratios of 0.43, 0.50, 0.60, 0.70 and 0.75 were installed downstream of the flow conditioner and operated at a Reynolds number of 54700 in a 50.4 cm pipe. Increasing the flow along the centreline of the pipe decreased the pressure drop across the orifice plate, resulting in increased discharge coefficients. The opposite was observed as the flow along the pipe centreline was decreased. The errors increased with increasing β ratio. A swirl generator was installed upstream of the β = 0.43 and 0.50 orifice plates. The swirl produced effecs opposite to the axial velocity. The change in discharge coefficient increased with decreasing β ratio.

Development of the mean velocity distribution in rectangular jets

The mean flowfield of 1 x 2 and 1 x 4 aspect ratio rectangular jets has been measured using a laser Doppler anemometer system. The development of the downstream velocity distribution is analyzed with respect to centerline velocity decay, shear layer growth, axis switching, and velocity profile development. Comparisons are made with axisymmetric, planar, and other rectangular jets. 23 refs.

Advantages of orthogonal and non-orthogonal three-dimensional anemometer systems

Abstract The propagation of uncertainties in the velocity components directly measured by a three-dimensional (3D)anemometer system into an orthogonal mean velocity vector and Reynolds stress tensor are investigated. Additional analysis is performed to investigate the effect of non-coincidence in the measured covariance terms and how they effect the accuracy of the orthogonal Reynolds stress tensor. A technique for evaluating the quality of measured covariance terms is presented.

An experimental technique for performing 3-D LDA measurements inside whirling annular seals

Abstract During the last several years, the Fluid Mechanics Division of the Turbomachinery Laboratory at Texas A&M University has developed a unique facility with the experimental capability for measuring the flow field inside journal bearings, labyrinth seals and annular seals. The facility consists of a specially designed 3D LDA system which is capable of measuring the instantaneous velocity vector within 0.2 mm of a wall while the laser beams are aligned almost perpendicular to the wall. This capability was required to measure the flow field inside journal bearings, labyrinth seals and annular seals. A detailed description of this facility along with some representative results obtained for a whirling annular seal are presented.

Flow field inside a whirling labyrinth seal

A 3D LDV was used to measure the velocity field inside a whirling labyrinth seal operating at a whirl ratio of one, an eccentricity ratio of 0.5, a Taylor number of 6600, and a Reynolds number of 24,000. The instantaneous velocity measurements were phase averaged to determine the mean velocity and Reynolds stress tensor for various rotor positions. The mean axial velocity reached both its maximum and minimum values in the throughflow region at the seal inlet. The maximum occurred on the suction side and the minimum on the pressure side. The wide variance in axial velocity magnitude decreased as the flow progressed through the seal then increased again near the exit, with the maximum axial velocity occurring on the pressure side and the minimum on the suction side. The azimuthal velocity steadily increased from the inlet to the exit with the circumferential variation decreasing from the inlet to the exit. The azimuthal velocity within a cavity was maximum over the upstream half of the cavity. The turbulence kinetic energy levels were largest when the axial velocity was maximum and when the variation between the fluids azimuthal velocity and the rotor surface were maximum. (Author)