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7th South East Asia Hydrocarbon Flow Measurement Workshop
5th – 7th March 2008
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Flow Conditioning and Effects on Accuracy for
Fluid Flow Measurement
Rick Rans, RANSolutions
Blaine Sawchuk, Canada Pipeline Accessories
Marvin Weiss, Coanda Research & Development Corp.
1 INTRODUCTION
Inferential meters, such as orifice, turbine and ultrasonic meters, infer fluid flow based on an
observedmeter output combined with a number of fluid flow assumptions. Optimal flow
conditions lead to optimal meter performance and in some cases “fully developed turbulent
pipeline flow” is used to describe these optimal flow conditions. Unfortunately the length of
long/straight/uniform/clean pipe required to produce “fully developed pipeline flow” often
exceeds practical installation constraints.Although flow conditioning has been successfully
used to create optimal flow conditions and reduce meter run lengths, problems can still exist if
they are incorrectly applied. This overview presents material available from the literature
which describes some of the installation effects that need to be managed.
2 WHAT IS “FULLY DEVELOPED TURBULENT PIPELINE FLOW”?
“Fully developed pipeline flow”occurs in long/straight/uniform/clean pipe when the pipe wall
friction effects completely control the fluid flow characteristics. It occurs at the point where
these characteristics no longer change as the fluid flows further downstream in
long/straight/uniform/clean pipe. Figure 1 shows the pictorial development of pipeline flow.
Even though flow enters the pipe with a uniform inlet velocity,the pipe wall boundary layer
influence on the flow profile increases until it reaches the center of the pipeline flow. Reynolds
Number and pipe wall surface roughness control the entrance length (Le) required to cause
fully developed turbulent flow. With uniform inlet conditions this length can be >100D. Add to
this additional inlet flow perturbations and the required pipe length canincrease.
Figure 1 – Fully Developed Turbulent Pipeline Flow
Characteristics such as swirl, flow profile, and turbulence intensity can be used to describe
pipeline flow. Some examples of these measurements are:
• Figure 2 is an example of full body swirl in bare pipe 10 diameters downstream of two 90o
elbows out of plane. [1] The red arrows show the direction and magnitude of the swirl
superimposedon the axial flow profile.
• Figure 3 shows measured and expected values of the axial/cross-flow velocity and
turbulence profiles. The measurements were taken in a meter proving facility prior to the
start of meter testing. [2]
This information can be used to help understand if the flowing conditions are stable and what
the effect these instabilities and flow changes have on the meterperformance.
Laminar Boundary Layer
Turbulent Boundary Layer
Le
Entrance Length of Developing Flow Fully Developed Turbulent Flow
u u u
7th South East Asia Hydrocarbon Flow Measurement Workshop
5th – 7th March 2008
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Figure 2 – Velocity Profile with Swill
Figure 3 – Axial/Cross-Flow Velocity and Turbulence Measurements – “Good Flow”
7th South East Asia Hydrocarbon Flow Measurement Workshop5th – 7th March 2008
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3 EFFECTS OF FLOW CONDITIONS/CONDITIONERS ON METER PERFORMANCE
The effect of meter inlet velocity profile conditions has been discussed extensively and
installation effect test results published in GRI test report for orifice [3], turbine [4] and
ultrasonic meters [1]. GERG have also published ultrasonic meter installation effect test
results [5]. Although swirl angleand velocity profile have been measured and their effects
recorded, turbulence effects have often been over-looked.
3.1 Swirl and Velocity Profile
The detrimental effects of swirl on orifice and turbine meters have been know for many years.
Once swirl has been created by a flow disturbance, the pipe wall roughness of long straight
pipe only has a limited effect and only causes the swirl to...