7 Meridional Through-Flow Analysis
The term meridional through-flow analysis refers to an analysis of the flow in the meridional plane, i.e., a plane defined by a constant polar angle of cylindrical coordinates. A solution in the meridional plane can completely characterize the flow field if the flow is locally axisymmetric. This is usually considered to be a reasonable approximation for hub-to-shroud computing stations located outside of the blade rows. Hence, common practice is to locate all hub-to-shroud computing stations in a meridional through-flow analysis before, between or after the blade rows. This requires a means to define the influence of the blade rows in a form that can be imposed on the solution. Typically, this is accomplished by specifying the flow angle or swirl velocity and the entropy rise or total pressure loss associated with flow passing through the blade row. In the case of performance analysis of an existing axial-flow compressor design, the empirical models of Chapter 6 can be used. When designing an axial-flow compressor, the influence of the blade rows is specified directly. When the meridional through-flow analysis is completed, the geometry of the blade rows is selected to produce the specified influence.
A properly formulated meridional through-flow analysis is a very powerful technique that can be used to support a variety of axial-flow compressor aerodynamic design and analysis functions. In this book, this technique will be used for aerodynamic performance analysis, general stage design and complete axial-flow compressor design. This chapter develops the governing equations and describes methods of solution appropriate to these various applications.