In many turbomachinery applications a compressor is directly driven by a turbine; for turbocharger applications a centrifugal compressor is usually adopted which is generally driven by a radial flow turbine, although mixed flow or axial flow turbines are occasionally required. A non-dimensional design procedure is developed to provide the basic dimensions and blade angles of centrifugal compressor impellers, whilst accounting for the turbine conditions as assessed through the matching requirements. The design of the turbine is then considered further in Part B.
The procedure can be applied for any desired compressor pressure ratio and target efficiency to develop an initial non-dimensional skeleton design. No other parameters are required from the initial specification and the design is developed non-dimensionally without recourse to empirical loss models and the associated uncertainties as the target efficiency must be specified. The procedure provides graphical information with respect to the impeller discharge conditions and inlet conditions from which the designer must select the most appropriate design. The screen graphics interface enables the designer to search across the design options; as this search is carried out numerical data are displayed and continuously up-dated to provide immediate information on which an infnrmed assessment can be based.
In addition to the compressor design options which are provided the matching conditions for the drive turbine provides information, such as specific speed, non-dimensional mass flow rate and pressure ratio, relevant to the turbine design. Judgements with respect to the design options for the compressor can then be made with the consequences for the associated turbine design clearly in view.
The non-dimensional design can be translated into an absolute design through the specification of the required mass flow rate and the inlet stagnation pressure and temperature.