Problems of Modern Pump and Turbine Design

Abstract

Abstract This is a general review of the present status of design principles which apply equally to centrifugal pumps and hydraulic turbines. The author first develops step by step the fundamental ideas underlying the theoretical behavior of a runner having an infinitely large number of thin blades which guide the fluid perfectly. The resemblance between the blading ordinarily used and the wing of an airplane has led to analysis on the basis that each blade acts as an airfoil. The author points out the many limitations of this theory and advocates a new beginning, taking as a starting point the theoretically perfect runner. By decreasing the number of blades first from infinity to a finite but very large number, he analyzes the forces and influences that are at work. Although he does not claim to have arrived at a final solution, he demonstrates the play of one effect upon another, and suggests that further experimentation should assist in making proper allowances for the uncertainties not subject to strict analysis and which become more and more important as the number of blades is reduced. The final section deals with the best conditions for the design of high-speed runners. The influence of the principal figures of layout upon which both efficiency and cavitation are dependent are discussed, and complete curves for efficiency and cavitation coefficient are given for three different specific speeds. This speed is defined by the same figure for pumps and turbines. He feels that both theories in spite of their defects can be used to advantage as experimental knowledge is progressively increased, and demonstrates that mathematics will throw light on a number of vital problems dealing particularly with efficiency and cavitation. He suggests for consideration a special type of profile, and expresses the hope that by combining the laboratory with theory, it will be possible to realize improvements in existing equipment, and finally to build up a strict method for pump and turbine design meeting properly and satisfactorily all of the requirements for high specific speed and small number of blades.