Experimental Study of the Influence of Roughness Change in a Piping on the Flow Measurement

In measurement of an ultrasonic flowmeter, the flow rate in piping is obtained using some measurement signals along the “chord” of the circular cross section of the piping. As for the “Chordal type ultrasonic flowmeter”, the flow rate is obtained by four (or eight) “chords”. The wall roughness influences the velocity profile. To evaluate the influences of roughness change on the measurement using four velocity points, a water test was performed. The Reynolds (Re) number of the test ranges from 4×10⁵ to 3×10⁶. It was suggested that high precision measurement in the range of high Re number can be expected in the smooth pipe. In the wall where sand of 0.1mm diameter was pasted, no difference in the velocity profile with the smooth wall was observed. A change in the velocity profiles appeared in the rough surface pipe where sands of 0.6mm and 0.2mm diameter has been pasted. Bias error (E_SL) was used to estimate the uncertainty of the flow rate measurements using four velocity points. The difference of each E_SL value based on the influence of roughness tended to diminish as the Re number increased. And the Re number dependency of E_SL is small, especially in the high Re number side. It suggests that an actual flow rate test for the high Re number to confirm the influence of roughness would not be necessary.