Development of a Mathematical Compressor Model to Predict Surge in a Closed Loop Brayton Cycle Available to Purchase

The accuracy by which the compressor performance is estimated plays a major role in predicting the transient performance of a gas turbine Brayton cycle. Numerical prediction has proven to be a valuable tool to reduce development costs of such cycles. This document subsequently discusses the expansion of the well-known Greitzer prediction model used for unstable transient compressor operation. The expansion allows for compressibility effects in the compressor as well as integrating the compressor with a turbine in an open cycle. After this it addresses the effect of flow feedback to the compressor inlet due to a closed cycle configuration. From the one-dimensional form of the conservation laws, three partial differential equations are derived governing the dynamics of fluid flow through the compressor. The simulation results for a simple open cycle configuration compares favorably with that published by Greitzer. A similar approach was used for the closed cycle resulting in an oscillation in compressor inlet pressure due to the feedback from the turbine outlet. The study presents a first step into investigating the possibility of including a generic surge and rotating stall model into an existing software code capable of solving complex thermodynamic systems including turbo-machine cycles.