Computational modeling of bed material shear stresses in piston-type erosion rate testing devices

The sediment erosion rate flume (SERF) device was computationally modeled using CD-adapco\u27s Star-CCM+ at varying flow rates and sample roughnesses so that wall shear stresses could be evaluated during a piston-style erosion test. Shear stress data were matched between the model and data from previous physical tests. Pressure differential upstream and downstream from an eroding specimen displayed similar behavior during both physical and modeled tests in that as eroding sample roughness increased, pressure differential did not appear to change. A series of complicated bed configurations were added to the computational model to quantify the effects of blocking, chunking, or sample overadvancement during an erosion test. Results appeared to indicate that small deviations in sample geometry may have large effects on localized shear stresses. Another series of models was run to provide an explanation for the beginning of blocking or chunking as a result of shear stress development over a rough sample. Results showed that relatively large localized shear stresses may develop simply because of the introduction of roughness. Finally, results also indicated that the most conservative method for future testing is to keep the bottom edge of an eroding sample flush with a flume bottom. © 2014 American Society of Civil Engineers