Page 151 - Fluid Mechanics and Thermodynamics of Turbomachinery

132 Fluid Mechanics, Thermodynamics of Turbomachinery
The starting behaviour of the Wells turbine

When a Wells turbine is started from rest the incoming relative flow will be at
90 degrees to the rotor blades. According to the choice of the design parameters
the blades could be severely stalled and, consequentially, the tangential force Y
will be small and the acceleration negligible. In fact, if and when this situation
occurs the turbine may only accelerate up to a speed much lower than the design
operational speed, a phenomenon called crawling. The problem can be avoided
either by choosing a suitable combination of hub/tip ratio and solidity values at the
design stage or, by some other means such as incorporating a starter drive. Values
of hub/tip ratio and solidity which have been found to allow self-starting of the
Wells turbine are indicated in Figure 4.28.

References

Ainley, D. G. and Mathieson, G. C. R. (1951). A method of performance estimation for axial
flow turbines. ARC R&M 2974.
Cooke, D. H. (1985). On prediction of off-design multistage turbine pressures by Stodola’s
ellipse. J. Eng. Gas Turbines Power, Trans. Am. Soc. Mech. Engrs., 107, 596 606.
Craig, H. R. M. and Cox, H. J. A. (1971). Performance estimation of axial flow turbines.
Proc. Instn. Mech. Engrs., 185, 407 424.
Den Hartog, J. P. (1952). Advanced Strength of Materials. McGraw-Hill.
Dunham, J. and Came, P. M. (1970). Improvements to the Ainley Mathieson method of
turbine performance prediction. Trans Am. Soc. Mech. Engrs., J. Eng. Power, 92, 252 6.
Dunham, J. and Panton, J. (1973). Experiments on the design of a small axial turbine. Confer-
ence Publication 3, Instn. Mech. Engrs.
Egli, A. (1936). The flow characteristics of variable-speed reaction steam turbines. Trans.
Am. Soc. Mech. Engrs., 58.
Emmert, H. D. (1950). Current design practices for gas turbine power elements. Trans. Am.
Soc. Mech. Engrs., 72, Pt. 2.
Freeman, JAW. (1955). High temperature materials. Gas Turbines and Free Piston Engines,
Lecture 5, University of Michigan, Summer Session.
Gato, L. C. and Falc` ao, A. F. de O. (1984). On the theory of the Wells turbine. J. Eng.
Power, Trans. Am. Soc. Mech. Engrs., 106 (also as 84-GT-5).
Horlock, J. H. (1958). A rapid method for calculating the “off-design” performance of
compressors and turbines. Aeronaut. Quart., 9.
Horlock, J. H. (1960). Losses and efficiencies in axial-flow turbines. Int. J. Mech. Sci. 2.
Horlock, J. H. (1966). Axial Flow Turbines. Butterworths. (1973 reprint with corrections,
Huntington, New York: Krieger.)
Japikse, D. (1986). Life evaluation of high temperature turbomachinery. In Advanced Topics
in Turbomachine Technology. Principal Lecture Series, No. 2. (David Japikse, ed.) pp. 5 1
to 5 47, Concepts ETI.
Kacker, S. C. and Okapuu, U. (1982). A mean line prediction method for axial flow turbine
efficiency. J. Eng. Power. Trans. Am. Soc. Mech. Engrs., 104, 111 9.
Kearton, W. J. (1958). Steam Turbine Theory and Practice. (7th edn). Pitman.
Le Griv` es, E. (1986). Cooling techniques for modern gas turbines. In Advanced Topics in
Turbomachinery Technology (David Japikse, ed.) pp. 4 1to4 51, Concepts ETI.