The Effects of Leading Edge Blade Thickness, Strike Velocity, and Fish Orientation on the Survival of Fish Passing Through Turbines

As part of ongoing efforts to develop environmentally-enhanced hydro turbines, EPRI has been conducting studies to assess turbine blade design parameters that affect mortality of fish struck by a blade during turbine passage.  Prior to the current study, testing with several blade thicknesses, strike velocities, and fish lengths was conducted with three species of fish.  The primary focus of these initial blade strike tests 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.  Unfortunately, an average correction factor does not work well for all test conditions and it is important to understand the reason for the higher mortality rates in the blade strike tests.  One obvious factor is that fish were oriented perpendicular to the blade in strike tests, whereas they were likely oriented about 45 degrees to the blade when passing through the Alden turbine.  This difference in orientation may have a greater effect on strike survival for some L/t ratios and impact velocities compared to others.  To address this issue, EPRI is conducting additional tests to examine the effects fish orientation (or angle) so that more reliable predictions can be made for a wide range of turbine designs.  Tests with angled fish are being conducted with the same facility and at the same velocities used in the previous studies with fish oriented perpendicular.   We will present the results of these tests and discuss the effect of fish orientation on blade strike mortality and how it can be factored into theoretical models for predicting turbine passage survival, as well as the design of fish-friendlier turbines.