EnginSoft - Conference Abstracts

EnginSoft International Conference 2010
CAE Technologies for Industry

Ejectors in a compressible network for gas turbine extended operability

Rossin S. - GE Oil&Gas (Italy)
Sassetti D. - GE Oil&Gas (Italy)

Abstract

Gas turbines are generally optimized to work at full load conditions. To extend their operability to partial load while still keeping NOx emissions under control, some critical issues must be addressed. The turbine wheel spaces are cooled with air extracted from one of the early compressor stages; under partial load the compressor bleed pressure reaches a value slightly lower than that of the turbine wheels, making the cooling ineffective and in the worst case, even creating the possibility of reverse flow that must be avoided.
In order to overcome this scenario, a solution employing an ejector has been implemented. This solution avoids reverse flow by mixing air extracted from one of the last compressor stages with the air extracted from an early stage.
A dedicated Flowmaster network was developed to validate this solution. The model includes compressor stages as well as the turbine wheel spaces pressure and temperature maps through 3D surfaces as a function of operating parameters (IGV, ambient temperature).
Since ejector components are currently not available for compressible networks in the Flowmaster code, a special algorithm that acts like a connection between three disjoint-networks was implemented. In order to match all the conditions at the network branches interfaces Flowmaster will make use of performance surfaces correlating the suction flow with the pressure difference between ejector exit and suction inlet.