Surge Avoidance in Gas Turbines

In this work, the transient process of surge has been investigated numerically in a gas turbine engine. A one-dimensional stage-by-stage mathematical model has been developed which can describe the system behavior during aerodynamic instabilities. It is demonstrated that, these instabilities can be stabilized by the use of active control strategies, such as air bleeding and air injection. Both steady and unsteady active control systems were considered. In the steady case, mass is removed at a fixed rate from the diffuser, or mass is injected at a fixed rate into the first stage of the compressor. In unsteady control, the rate of bleeding or injection is linked with the amplitude and the frequency of the upstream pressure disturbances. Results show that both steady and unsteady strategies eliminate surge disturbances and suppress the instabilities. Therefore, they extend the stable operating range of compressor. It is also shown that smaller amount of compressed air needs to be removed in the unsteady control case. Also, a variable area diffuser is shown to be able of suppressing surge instabilities. Active control of instabilities, caused by sinusoidal perturbations of inlet total pressure, was also investigated, which showed to destabilize the stable operating condition the design point.