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 Table 4.7.1
Summary of Turbine Venting
Characteristic
Description
Targets
Low DO levels of the release waters commonly
associated with hydropower generation during strati-
fied periods and anoxic conditions.
Mode of action
Injection of air downstream of the turbine runner
blades to increase the DO levels of the release waters.
Effectiveness
Up to 30 percent of the DO deficit may be satisfied by
this technique.
Longevity
Based on the life of the turbine; years.
Negative features
Slight reduction in the generating efficiency and,
consequently, the related revenues. Possible nitrogen
supersaturation. Possible increase in the wear on the
turbines
Costs
Low to Moderate depending on the required modifi-
cations to the turbines.
Applicability to reservoirs
Very applicable to hydropower projects.
4.7.3.3 Design Methodology
Numerical and physical models have been used to predict the aeration performance and
hydraulic performance of various auto-venting alternatives. A detailed description of the current state
of the art for auto-venting technology is included in a report prepared for the US Department of Energy
Advanced Hydro Turbine Program (Franke et al., 1997). The basic requirement of the auto-venting
design is to provide air supply passageways to subatmospheric pressures areas within the turbine.
Numerical models used for turbine hydraulic performance design are frequently used to determine the
location of these low pressure areas, exist or determine where they can be created. Other numerical
models are used to predict the oxygen transfer to the water once the air is entrained into the water flow
(Ventikos et al., 1998, Wilhelms et al., 1987, Buck et al., 1980) . Physical models have been used to
evaluate the performance of various air passageway alternatives and choose optimal designs (March et
al., 1991, March et al., 1992). Interpretation of physical model results requires scaling relationships
such as those developed by Thompson and Gulliver (1997). Overall, the prediction of the performance
of a hydroturbine with two-phase air/water flow is extremely complicated and site specific. However,
4.7-6
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