Session D4 - The Science Behind a Fish-Friendly Turbine

Fish passing through hydro-turbines are subject to abrasion along surfaces and in small gaps, impact on stay vanes and gates, strike by leading blade edges, rapid pressure drops, flow shear and minimum pressures, all of which may cause injury and even death (Aada, G. et al. 1997). Limiting acceptable values for the flow induced mechanisms concerning pressure and shear have been established and were used in designing the Alden turbine. To determine how well these criteria have been met in various parts of the turbine, computational fluid dynamics (CFD was used to predict the locations and volumes which meet or exceed these limiting values. To gain confidence in the predictions, verification of the CFD simulations was performed by comparing the efficiency hill chart derived from CFD simulations with that resulting from physical scale model tests of the Alden turbine. Efficiency is an indicator of flow conditions in the runner. Thereafter, the CFD simulations were used to predict flow parameters related to the allowed limits for shear, pressure change rates, and minimum absolute pressures. In addition, EPRI has been supporting studies to assess hydro-turbine leading edge blade design parameters that affect fish mortality. Initial testing was conducted with three fish species and several blade thicknesses, strike velocities, and fish lengths. The primary focus of these initial studies was to determine how the ratio of fish length to blade thickness (L/t ratio) influenced strike mortality and to provide data that could be used to improve the fish-friendliness of hydro turbines. However, comparing predicted fish survival to the measured survival of the pilot-scale Alden turbine revealed that the mortality predicted from the blade strike data was higher by about 40% on average. One factor that could account for this difference is that fish were oriented perpendicular to the blade in the strike tests, whereas they were likely oriented about 45 degrees to the blade when passing through the Alden turbine. Therefore, additional tests were conducted to examine the effects fish orientation so that more reliable predictions can be made for a wide range of turbine designs. We will present the results of these tests and discus the effect of strike speed and leading edge blade thickness on strike mortality. These parameters are factored into theoretical models for predicting turbine passage survival and the design of fish-friendlier turbines