Fig.F-27 Dependence
of the speed coefficient
upon rotor geometry and
achieved efficiency of
radial centripetal turbines.
Similarly as for pumps
(Fig.F-20) there is a flat
optimum near 1 rad.
Water turbines are
usually large and for
easier transportation,
it is common to choose
conditions leading to
larger speed coefficient
- similarly as in Fig.F-20
larger value of the
coefficient leads to
smaller rotor diameter
and thus smaller overall
dimensions.

Hydrodynamic couplings and torque converters: - are, in principle, a combination of a pump and a turbine in a single case. The disadvantage of couplings is that if there is to be transmitted some torque, some inevitable slip must be accepted: output speed is lower than input speed. This is documented on the example of the coupling characteristic in lower left-hand part of Fig.F-28. On the other hand, the capability of running in the slip condition may be an advantage: there is no wear, the driving engine starts unloaded. The changes of the output speed with varied torque are continuous and smooth. The transferred torque is automatically limited. Shocks and vibrations from both sides are damped. The torque converters possess another, stationary system of blades - the stator (and sometimes other additional wheels). They can function as a gearbox.
Fig.F-28


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This is page Nr. F11 from textbook Vaclav TESAR : "BASIC FLUID MECHANICS"
Any comments and suggestions concerning this text may be mailed to the author to his address tesar@fsid.cvut.cz

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