Improving Ultrasonic Flow Meter
Accuracy Using Proprietary Flow
Profile Correction Techniques
Practical flow measurement solutions for non-conformingstraight runs
For decades, the Panametrics line of ultrasonic flow meters
has proven to be the reliable solution for challenging gas
flow measurement applications. Leveraging Panametric’s
vast experience in aircraft engine design and by using
Computational Fluid Dynamics (CFD), Panametrics hascompiled a body of work resulting in the ability to implement
ultrasonic flow profile accuracy correction factors for avariety of piping run conditions that compare favorablyto accuracies normally obtained in straight runs of 20diameters or more.

Using advanced technologies
to overcome limited available
straight runs
Maintaining accuracy in applications with limited straightrun has been, and remains today an industry challenge. In
gas flow measurement, ideal conditions require upstream
straight runs as much as 20 diameters or more. In practice,
this may be difficult, costly, or in some cases impossible toachieve. The stakes can be enormous, as re-laying new piperuns to accommodate increased straight runs can easily
amount to a huge cost.
Recognizing the challenges associated with limited straightrun requirements, Panametrics developed a process to

Actual Flow Profile Model of Piping Installation

quantify pipe bend and other effects on flow profiles undera wide range of conditions. In most cases CFD analysis canaccommodate pipe runs as short as 6 diameters upstream
and 2 diameters downstream, with minimal effects on meter
accuracy.
Especially useful in hot tap or cold tap applications when
existing piping limits meter straight run, flow profile modelingprovides dynamic flow correction that in most cases meetsor exceeds accuracy requirements.

How flow profile correction works
Providing Panametrics with an isometric drawing ofan existing or planned installation that requires a flow
measurement, along with the process parameters,
Panametric’s engineering team models the flow and defines
a set of correction factors that will cover a wide range offlow and process conditions. These correction factors arethen entered into the transmitter and act as a calibration
correction curve over the range of flow velocities.
Added inaccuracy for a flow profile corrected straight-runwill typically be in the 0.5% to 1.5% range, depending on theactual available straight run, process conditions, and thecomplexity of the upstream disturbances. Consider thatmany non-conforming, uncorrected straight runs may add
10% or more of additional inaccuracy to a flow meter reading,essentially rendering the meter non-compliant in manyapplications.
The chart at the right illustrates the range of flow correction
factors as a function of meter position for a selected meter
configuration, in this case, a horizontal diameter path. Noticethat in this configuration added inaccuracy can be as much
as 6% at 15 L/D*, even at very high flow velocities. Flow profile
corrections aid in defining the optimum path configurationand meter placement to minimize meter inaccuracy.
Nearly all installations can benefit from some form of profile
correction, especially in low density fluids like gas, to improveoverall system accuracy.

What CFD is not
CFD is NOT a calibration. A meter corrected with CFD
modeling is no more accurate than if the same meter wasplaced in a position with a fully developed flow profile. Infact, relative to a fully developed flow profile, assuming 20
diameters or more of straight run, there is added inaccuracy
due to calculation modeling and meter positioning. As noted
earlier, typical added inaccuracy for a non-fully developed
flow that is compensated with CFD is about .5% to 1.5%;
however, this can vary widely by application.
In some cases, depending on the complexity of the upstream
disturbance, CFD may not be able to compensate for theundeveloped flow profile. This is a risk that one must consider
before purchasing a CFD analysis. Unfortunately the resultsof the profiling are not known until it is complete. If this does
occur, a piping modification may allow for a CFD profile
correction to succeed, but this is not known for sure until
another CFD analysis is completed. These considerations need
to be weighed before pursuing a CFD correction, but relative toadding more straight run, CFD may still be the best choice.

Ordering information for a flow profile analysis
Part number
FLOW SPECIAL-CFD
Description
Five point flow profile correction
Requirements
Isometric of piping to be analyzed starting at the seal
or knock-out drum, ending 8 diameters past the last
disturbance of the meter run, and a completed applications
data sheet detailing the flow conditions.
Pricing
Contact your Panametrics representative for a quote.
Lead Time
A typical profile correction analysis will require from two
to four weeks of programming and computer run time.
Depending on the queue, lead time may vary.
Deliverables• Summary report of results of the flow profile modeling• Recommended location of the flow meter• Recommended flow meter configuration• A series of five correction factors by flow velocity• Meter total inaccuracy at each correction point• A presentation of the details of the flow profile analysis* L/D denotes length in pipe diameters.

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BHCS38524		

(09/2020)

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