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Chapter 13
Axial Compressors
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_13
Abstract The chapter starts with an analysis of the circumferentially averaged flow
on the mean radius of an axial compressor. Loss representation is discussed together
with the diffusion factor concept for estimating the loading capacity of blade rows.
A further step is an analysis of the radial variation of flow parameters, but without
taking into account the effect of boundary layer flows on the hub and casing. This
flow is called the primary flow. A next aspect is the difference between the complete flow and the primary flow, the so-called secondary flow. The different vortex
patterns in the secondary flow are described. All considerations together allow a
conclusion on the optimal radial distribution of the flow parameters in an axial compressor. Some aspects of three-dimensional blade shaping conclude the flow study.
Next, blade profile shapes for subsonic, supercritical, transonic and supersonic
cascades are studied. The chapter concludes with a discussion on the performance
characteristics and the operating limits due to surge and choke.
13.1 Mean Line Analysis
The term mean line analysis refers to an analysis on the average radius. Assumed
is that the flow on the average radius is representative for the flow along the entire
span. The simplifications are: steady flow; no radial velocity components; no circumferential variations; constant axial velocity through the stage. The analysis is
one-dimensional in the sense that changes of parameters only occur with the axial
coordinate: tangential velocity component, pressure and density. In a real compressor, the axial velocity component may decrease somewhat within a stage. There
is also a decrease of the radial height of the stage, causing small radial velocity
components. Periodic variations occur in the circumferential direction due to the influence of the blades. We here consider flow parameters averaged in the circumferential direction. These averaged parameters are steady for constant rotational speed.
Chapter 13
Axial Compressors
© Springer Science+Business Media Dordrecht 2015
E. Dick, Fundamentals of Turbomachines, Fluid Mechanics and Its Applications 109,
DOI 10.1007/978-94-017-9627-9_13
Abstract The chapter starts with an analysis of the circumferentially averaged flow
on the mean radius of an axial compressor. Loss representation is discussed together
with the diffusion factor concept for estimating the loading capacity of blade rows.
A further step is an analysis of the radial variation of flow parameters, but without
taking into account the effect of boundary layer flows on the hub and casing. This
flow is called the primary flow. A next aspect is the difference between the complete flow and the primary flow, the so-called secondary flow. The different vortex
patterns in the secondary flow are described. All considerations together allow a
conclusion on the optimal radial distribution of the flow parameters in an axial compressor. Some aspects of three-dimensional blade shaping conclude the flow study.
Next, blade profile shapes for subsonic, supercritical, transonic and supersonic
cascades are studied. The chapter concludes with a discussion on the performance
characteristics and the operating limits due to surge and choke.
13.1 Mean Line Analysis
The term mean line analysis refers to an analysis on the average radius. Assumed
is that the flow on the average radius is representative for the flow along the entire
span. The simplifications are: steady flow; no radial velocity components; no circumferential variations; constant axial velocity through the stage. The analysis is
one-dimensional in the sense that changes of parameters only occur with the axial
coordinate: tangential velocity component, pressure and density. In a real compressor, the axial velocity component may decrease somewhat within a stage. There
is also a decrease of the radial height of the stage, causing small radial velocity
components. Periodic variations occur in the circumferential direction due to the influence of the blades. We here consider flow parameters averaged in the circumferential direction. These averaged parameters are steady for constant rotational speed.