A novel approach to calculate the performance map of a centrifugal compressor stage is presented. At the design point four nondimensional parameters (the flow coefficient φ, the work coefficient λ, the tip-speed Mach number M, and the efficiency η) characterize the performance. In the new method the performance of the whole map is also based on these four parameters through physically based algebraic equations which require little prior knowledge of the detailed geometry. The variable empirical coefficients in the parameterized equations can be calibrated to match the performance maps of a wide range of stage types, including turbocharger and process compressor impellers with vaned and vaneless diffusers. The examples provided show that the efficiency and the pressure ratio performance maps of turbochargers with vaneless diffusers can be predicted to within ±2% in this way. More uncertainty is present in the prediction of the surge line, as this is very variable from stage to stage. During the preliminary design the method provides a useful reference performance map based on earlier experience for comparison with objectives at different speeds and flows.

This paper describes a newly developed streamline curvature throughflow method for the analysis of radial or mixed flow machines. The code includes curved walls, curved leading and trailing edges, and internal blade row calculating stations. A general method of specifying the empirical data provides separate treatment of blockage, losses, and deviation. Incompressible and compressible fluids are allowed, including real gases and supersonic relative flow in blade rows. The paper describes some new aspects of the code. In particular, a relatively simple numerical model for spanwise mixing is derived, the calculation method for prescribed pressure ratio in compressor bladed rows is described, and the method used to redistribute the flow across the span due to choking is given. Examples are given of the use and validation of the code for many types of radial turbomachinery and these show it is an excellent tool for preliminary design.

This paper describes a newly developed streamline curvature throughflow method for the analysis of radial or mixed flow machines. The code includes curved walls, curved leading and trailing edges, and internal blade row calculating stations. A general method of specifying the empirical data provides separate treatment of blockage, losses, and deviation. Incompressible and compressible fluids are allowed, including real gases and supersonic relative flow in blade rows. The paper describes some new aspects of the code. In particular, a relatively simple numerical model for spanwise mixing is derived; the calculation method for prescribed pressure ratio in compressor blade rows is described; and the method used to redistribute the flow across the span due to choking is given. Examples are given of the use and validation of the code for many types of radial turbomachinery, and these show that it is an excellent tool for preliminary design.

An equation is derived that relates the changes in turbomachinery efficiency with Reynolds number to the changes in the friction factor of an equivalent flat plate. This equation takes into account the different Reynolds number and roughness dependencies of the individual components, and can be used for whole stages and multistage machines. The new method is sufficiently general to correct for changes in Reynolds number due to changes in fluid properties or speed, changes in machine size, or changes in the surface roughness of components for all types of turbomachinery, but is calibrated here for use on axial and radial compressors. The method uses friction factor equations for a flat plate which include fully rough behaviour above an upper critical Reynolds number, a transition region depending on roughness and a region with laminar flow below the lower critical Reynolds number. The correction equation for efficiency includes a single empirical factor. Based on a simple loss analysis and a calibration with over 30 sets of experimental test data covering a wide range of machine types, a suggestion for the variation of this factor with specific speed has been made. Additional correction equations are derived for the shift in flow and the change in pressure rise with Reynolds number and these are also calibrated against the same data.

Centrifugal compressors are used in a wide range of applications in which performance and mechanical integrity are invariably among the paramount design objectives. There is therefore continuing interest in the development of a sound understanding of the relevant physical phenomena and in the systematic application of the knowledge base that is the forerunner of the established design procedures. The paper reviews centrifugal compressor design methods that are commonly used in industry and reviews the underlying engineering science supporting the design practices. The design process, starting with the preliminary design and its reliance on empirical rules through to state-of-the-art aerodynamic design using computational fluid dynamics (CFD), is presented. The essentials of impeller mechanical design are also included in the paper.