received by the International Bureau on 22 August 2014 (22.08.2014)

What is claimed is:

1 . An ultrasonic flow metering system, comprising:

an ultrasonic flow meter comprising a pair of ultrasonic transducers arranged to exchange ultrasonic signals through a fluid stream flowing between the transducers;

a flow conditioner disposed upstream of the ultrasonic flow meter;

a reducer disposed between the flow conditioner and the ultrasonic flow meter to reduce the cross-sectional area of the fluid stream flowing from the flow conditioner to the ultrasonic flow meter; and

an expander disposed upstream of the flow conditioner.

2. The system of claim 1 , wherein the flow conditioner and the reducer condition the fluid stream such that the ultrasonic flow meter measures velocity of the fluid stream with less than 0.2 percent error, wherein the fluid stream has a Reynolds number less than 1000.

3. The system of claim 1 , wherein the flow conditioner and the reducer condition the fluid stream such that the ultrasonic flow meter measures velocity of the fluid stream with less than 0.2 percent error and the fluid stream has a Reynolds number of no more than 500.

4. The system of claim 2, further comprising flow computation logic configured to compute volumetric flow through the ultrasonic flow meter using correction based on instantaneous profile factor of the fluid stream and meter factor; wherein meter factor is a ratio of a reference volume of discharge to a volume discharged by the ultrasonic flow meter within a predetermined time period.

5. The system of claim 4, wherein the reducer is a concentric Venturi reducer comprising an angle of reduction in a range of 8 degrees to 16 degrees.

6. The system of claim 1 , wherein the flow conditioner and the reducer condition the fluid stream such that a profile factor of the fluid stream varies during transitional flow of the fluid stream in a range of approximately 1 .18 to 1 .8.

7. The system of claim 1 , wherein the flow conditioner and the reducer reduce pressure loss in the system by over 75 percent relative to a flow metering system comprising a flow conditioner having a diameter equivalent to that of the flow meter.

8. The system of claim 1 , further comprising computation logic configured to compute Reynolds number and viscosity of the fluid stream during transitional flow based on instantaneous profile factor of the fluid stream.

9. The system of claim 8, wherein the computation logic is configured to compute the Reynolds number and viscosity with less than 5 percent error; wherein the fluid stream has a Reynolds number in a range of from 500 to 5500.

10. The system of claim 1 , further comprising a connection of the reducer to the ultrasonic flow meter comprising a surface roughness height of not more than 64 micro inches.

1 1. A method for ultrasonic metering, comprising:

connecting a downstream end of a reducer to an upstream end of an ultrasonic flow meter; and

connecting an upstream end of the reducer to a downstream end of a flow conditioner;

connecting a downstream end of an expander to the flow conditioner via a pipe section that is at least three pipe diameters in length; wherein an inner cross-sectional area of the downstream end of the reducer is smaller than an inner cross-sectional area of the upstream end of the reducer.

12. The method of claim 1 1 , further comprising measuring average velocity of a fluid stream flowing through the ultrasonic flow meter with no more than 0.2 percent error; wherein the fluid stream has a Reynolds number as low as 500.

13. The method of claim 1 1 , further comprising computing volumetric flow through the ultrasonic flow meter using a correction based on instantaneous profile factor of the fluid stream and meter factor; wherein meter factor is a ratio of a reference volume of discharge to a volume discharged by the ultrasonic flow meter within a predetermined time period.

14. The method of claim 1 1 , wherein the reducer is a concentric Venturi reducer comprising an angle of reduction in a range of 8 degrees to 16 degrees.

15. The method of claim 1 1 , further comprising reducing, via the flow conditioner and reducer, pressure drop across the flow conditioner in a range of 79 percent to 89 percent relative to pressure drop in a system comprising a flow conditioner of equivalent diameter to the ultrasonic meter.

16. The method of claim 1 1 , further comprising computing Reynolds number and viscosity of the fluid stream during transitional flow based on instantaneous profile factor of the fluid stream.

17. The method of claim 16, further comprising computing the Reynolds number and viscosity with less than 5 percent error; wherein the fluid stream has a Reynolds number in a range of from 500 to 5500.

18. An ultrasonic flow metering system, comprising:

a flow conditioner;

a reducer;

an expander; and

an ultrasonic flow meter;

wherein the flow conditioner is coupled to an upstream end of the reducer, the expander is coupled to an upstream end of the flow conditioner, and the ultrasonic flow meter is coupled to a downstream end of the reducer;

wherein the flow conditioner and the reducer condition a fluid stream flowing through the ultrasonic flow meter such that the ultrasonic flow meter measures velocity of the fluid stream with less than 0.2 percent error and with the fluid stream having a Reynolds number less than 5000.

19. The system of claim 18, further comprising at least three pipe diameters of straight pipe coupled to an upstream end of the flow conditioner.

20. The system of claim 18, wherein the fluid stream has a Reynolds number as low as 500.

21. The system of claim 18, further comprising flow computation logic configured to compute volume of the fluid stream based on a correction derived from instantaneous profile factor of the fluid stream and meter factor; wherein meter factor is a ratio of a reference volume of discharge to a volume discharged by the ultrasonic flow meter within a predetermined time period.

22. The system of claim 18, wherein the reducer is a concentric Venturi reducer comprising an angle of reduction in a range of 8 degrees to 16 degrees.

23. The system of claim 18, further comprising computation logic configured to compute Reynolds number and viscosity of the fluid stream during transitional flow based on instantaneous profile factor of the fluid stream.

24. The system of claim 23, wherein the computation logic is configured to compute the Reynolds number and viscosity with less than 5 percent error; wherein the fluid stream has a Reynolds number in a range of from 500 to 5500.

25. The system of claim 23, wherein computation logic is configured to compute the Reynolds number based on an eighth order polynomial function of the instantaneous profile factor of the fluid stream.

26. The method of claim 1 1 , further comprising conditioning the fluid stream, via the flow conditioner and reducer, such that the profile factor varies during transitional flow of the fluid stream in a range of approximately 1 .18 to 1 .8.