Rapid pressure changes in hydroelectric turbine flows can cause barotrauma that can be hazardous to the passage of fish, in particular migratory juvenile salmonids. Although numerous laboratory tests have evaluated the effect of rapid decompression in fish species of relevance, numerical modeling studies offer the advantage of predicting, for new turbine designs, the potential risks of mortality and injury from rapid pressure change during turbine passage. However, rapid pressure change is only one of several hydraulic risks encountered by fish during turbine passage in addition to blade strike, shear, and turbulence. To better understand the role of rapid pressure changes, the present work focuses on the application of a CFD-based method for evaluating the risk of pressure-related mortality to fish passing through a early 1960s era original hydroelectric Kaplan turbine design at Wanapum Dam (Columbia River, Washington, USA), and a modern advanced Kaplan turbine. The results show that the modeling approach acceptably reproduces the nadir pressure distributions compared to field data from an autonomous sensor previously collected at the site. Furthermore, the method also provides a quantitative evaluation of the risk of mortality to a fish population entering the turbine with a spacial distribution prescribed from field studies. Our findings show that the new advanced-design unit performs better, in terms of reduced barotrauma risk to fish from exposure to low pressures, than the original turbine unit. The outcomes allow for comparative analyses of turbine designs and operations prior to installation, an advantage that can potentially be integrated in the process of designing new turbine units to achieve superior environmental performance. Overall, the results show that modern turbine designs can achieve both hydraulic benefits such as increased power and lower cavitation potential while at the same time reducing barotrauma risks to passing fish.
Revised: September 15, 2016 |
Published: June 9, 2016