Effects of flow measurement on sloped pipes using ultrasonic flowmeter

Precision in flow measurement has economic consequences and also necessitates fulfillment of stipulated requirement of straight length upstream and downstream of flow meter. However, many times, the site constraints do not permit to fulfill this requirement. IEC 41(1991) recommends use of ultrasonic flow meter as a complimentary to other flow measuring techniques for hydro turbines. The motivation of the study is drawn from the typical water conductor system of hydro plants where the penstocks are generally sloped conduit in nature. The experimental investigation presented in this paper is to highlight and simulate the variation in accuracy for flow rate measurement for Reynolds number ranging from 0.8 ×10⁵ to 10 ×10⁵ with clamp-on ultrasonic flow meter with different sloped straight length considering upstream and downstream length as per the standards. The error in flow measurement by ultrasonic flow meter in straight length varied from -1.0% to +1.0% to the reference flow as per the acceptable level. Whereas, the increase of slope straight angle the percentage of shift in error is increases. The error in flow measurement of 6° degree pipe line was in the range of 4.0%. Similarly, the conduit of 12° degrees pipe line was up to 8%. The velocity distortion of the sloped pipes is also validated using commercial CFD Fluent solver. These findings are useful in selecting suitable location for the installation. Presently ultrasonic flow meters do not address the use at site conditions like sloped pipes. Therefore the existing ultrasonic flow metering techniques need attention for up gradation.