Real time thermodynamic transient model for three spool turboprop engine

Abstract

Previous real time engine models used for control development and test have utilized either linear techniques or simplified aero-thermodynamics. With the increased speed now available from dedicated PC based computer systems it was felt that it should be possible to develop a full aerodynamic and thermodynamic model of the engine that would have the capability to run in a real time bench environment and approach the accuracy of our best unlimited time models. The paper describes such a model that has successfully been produced for a three spool turboprop engine, and shows that it matches, in a real time environment, the transient performance of a model run with unlimited execution time. This model has the additional capability of starting from zero speed and running back down to zero speed on shut down, all in real time environment. The model was based on an existing model of a three spool turboprop engine which already included full transient heat transfer and volume dynamics effects. Modifications to this that were necessary to satisfy the requirement to model the starting regime and to decrease the convergence time resulted in a more efficient model methodology. The component map representation was changed as was the iteration logic, by removing internal iterations and by making the solver matrix more strongly diagonal. For the real time environment the code had to provide a solution within a maximum of 10 ms. The final real-time' model only differed from the modified full transient model in the use of the solver logic. The number of overall iterative passes were limited to two, and balances that were shown not to significantly modify the accuracy of the solution were removed. The net result of the work is the elimination of two simplified models.