Measured Stationary Waves in Hydraulic Sand Transport Downstream of a Bend
Type:
Presented during:
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
Authors:
A.M. Talmon, M. Gruszczyński, E. Meshkati
Abstract
"A sustainable and effective dredging/hydraulic transport of sand slurry requires a reliable monitoring of several key parameters, amongst them, local pressures throughout the transport system. The local pressure measurement of a slurry flow, however, can be deceptive, particularly downstream of hydraulic components such as bends. This study sheds light on the effect of a 180-degree bend on the slurry flow and the extent to which this effect may influence the pressure measurements downstream of the bend. Selected results from two experimental programs are combined and presented to serve the objective of this paper. The formation of stationary waves in the presence of two testing section lengths (3.4 m and 6 m), two different sand types (Dorsilit 9 and S60), and two different volumetric sand concentrations (24% and 28%) is experimentally studied. The measured longitudinal pressure profiles revealed the formation of stationary (standing) waves in the horizontal pipe downstream of the bend. The stationary waves are formed under the presence of a stratified flow sliding bed regime, manifesting themselves via variations in the thickness of the bed layer along the pipe. These waves occur at and above the deposit limit velocity, where most dredging applications are performed, as at this operation window, on the one hand, the risk of plugging is low, and, on the other hand, less energy is required. The stationary waves can significantly impact the local pressure measurements. The extension of these waves was found to be larger than what has been assumed as the typical affected distance downstream of a bend. Hence, the location and layout of pressure measurement points downstream of a bend should be defined carefully. We expect similar effects downstream of any other hydraulic components such as valves and pumps."
Keywords: Hydraulic transport, measurements, bend effect, morphology