How fish-friendly turbines work

June 24, 2008 at 7:09 am | Posted in Environmental, Power Plant | 2 Comments

Quantifying the fish injuries caused by a hydroelectric turbine often has been based more on model predictions than actual measurements. Survival rates measured for fish passing directly through a modern large turbine range from 88% to 94%. By comparison, fish bypass system survival rates typically range from 95% to 98% percent and from 95% to 99% percent for a spillway system.

It’s important to realize, however, that the net survival rates are substantially lower, because each fish has to pass through several turbines during its long journey to the sea (Figure 1).

1. Hydro turbine system: Fish-passage issues

Turbine-passage survival is a complicated function of gap sizes, runner blade angles, wicket gate openings and overhang, and water passageway flow patterns.

Source: U.S. Department of Energy

That’s why new fish-friendly turbine designs are a vital part of hydro’s future. The U.S. Department of Energy’s Advanced Hydropower Turbine System program has identified specific injury mechanisms, which include:

  • Turbulent flows or cavitation in turbine water passages resulting from low-efficiency designs or plant operating strategies where extremely low water pressures cause the formation of vapor bubbles, which subsequently collapse violently.
  • Turbulent flows and the trapping and cutting of fish in the zone of flow passing near the turbine hub when large gaps between blade and hub exist (characterizing the lower-output operation of Kaplan turbines).
  • Strike of fish by turbine blades or impact of fish on structures including runner blades, stay vanes, wicket gates, and draft tube piers.
  • Shear stress when two bodies of water of different velocities collide across a fish’s body. The highest values of shear stress are found close to the interface between the flow and solid objects it speeds by, such as the blade leading edges, vanes, and gates.
  • Rapid and extreme pressure changes (water pressures within the turbine may increase to several times atmospheric pressure, then drop to sub-atmospheric pressure, all in a matter of seconds).
  • Abrasion and grinding: Abrasion occurs with the rubbing action of a fish against rough turbine surfaces by flow turbulence and is dependent on flow discharge and velocity, number and spacing of turbine blades, and the geometry of flow passages. Grinding injury can occur when a fish is drawn into small clearances (gaps of sizes close to that of the fish) within the turbine system.
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  1. We are investigating the turbulent flows and their structure, precisely the shear stress, motion of additives (like a fish) in turbulent flows, etc.
    If there is some interest from the fish-passage-research side, we’d be glad to find a partner for the cooperative research on this subject: effect of turbulent flows on fish (incl. cavitation, shear stresses, pressure changes, etc.) We have optical experimental methods to work in clear water at a distance sufficient to measure 3D turbulent flow structure next to a fish (at his position, no need to “glue” it).
    http://www.eng.tau.ac.il/efdl

  2. […] 5, 2008 How fish-friendly turbines work « Power Generation That’s why new fish-friendly turbine designs are a vital part of hydro’s future. The U.S. […]


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