PHYSICAL ID MODEL OF A HIGH-PRESSURE RATIO CENTRIFUGAL COMPRESSOR FOR TURBOCHARGERS

摘要

The physical model of a centrifugal compressor aims at finding detailed information on values inside the machine, based on standard compressor map knowledge and basic geometry of a compressor. The model describes aerodynamics of flow from compressor inlet to outlet at a central streamline, if mass flow rate and impeller speed is known. The solution of basic conservation laws can yield unknown, cross-section averaged temperatures, pressures and velocities along central streamline for compressible fluid and treats transonic operation, as well. After the description of general methods for solving compressible fluid flow and transformation of radial blade cascades to axial ones, the system of equations is completed with empiric knowledge of compressor blade cascades - forces and losses. Howell theory is used for axial inducer and after conform transformation to radial blade diffuser cascade, as well. Radial vanes of a rotor are transformed fixing the same length of a blade and flow areas and flow separation at inducer outlet is taken into account. Specific procedure is developed for a vaneless diffuser with friction losses. Non-linear equations of gas dynamics have to be solved in numerical and iterative way with help of Newton-Raphson solver. The model treats transonic flow features in both compressor inducer and diffuser. The validation of the model will be published in the second paper focused to this topic. The model can be used for quasi-steady simulation in a 1D model, especially if compressor map extrapolation is required. The model predictions create virtual sensors for identification of directly unmeasurable quantities inside a compressor. It helps in better understanding in-compressor processes. Moreover, the model offers parameters for unsteady model, based on 1D modules for unsteady flow modelling.