OVERVIEW

This chapter examines the overall performance characteristics of centrifugal compressors. This material will familiarize the reader with the behavior of these machines, classified under the broad term turbomachinery. Pumps and compressors are used to produce pressure; turbines produce power. These machines have some common characteristics. The main element is a rotor with blades or vanes, and the path of the fluid in the rotor may be axial, radial, or a combination of both.

There are three methods of studying the elements of turbomachinery operation. First, by examining forces and velocity diagrams, it is possible to discover some general relationships between capacity, pressure, speed, and power. Second, comprehensive experimentation can be undertaken to study relationships between different variables. Third, without considering the actual mechanics, one can use dimensional analysis to derive a set of factors whose grouping can shed light on overall behavior. The analysis presented in this chapter shows the typical performance diagrams one can expect from turbomachines.

Aerothermodynamics is fundamental to the aerodynamics and thermodynamics of all types of turbomachines. Turbomachines are considered to be steady-flow machinery, operating with gases that have a low viscosity, and are rotating at a high velocity. The equations and processes described in this chapter govern all types of turbomachines with emphasis on the centrifugal compressor.

DIMENSIONAL ANALYSIS

In attempting to predict the behavior of a proposed design in engineering, several approaches are possible. One approach is to use empirical equations based upon previous experience in similar situations. This approach to...