Marco Micheli

Redesign of a Multistage Axial Compressor for a Heavy Duty Industrial Gas Turbine (GT11NMC)

Different approaches to compressor design exist in industrial practice. This paper describes two design philosophies that can be followed with compressor development (re-staggering and new airfoil design), and reports on field experience gained with an advanced compressor design using CDA (Controlled Diffusion Airfoils) profiles. The first philosophy described is based on incremental changes of compressor design, consisting of keeping the same blade profiles and re-staggering a number of rotor blades and/or stator vanes. The second philosophy described is to utilize advanced CDA profiles in compressor design, optimized for increased mass-flow and backpressure. The second philosophy was followed in the development of a compressor upgrade for ALSTOM’s GT11NM gas turbines, where a significant increase in GT power output (exceeding 10%) and improved overall engine efficiency (+0.4% additive) at unchanged surge margin were achieved. Power output and improved efficiency resulted solely from the advanced blade design, requiring no additional power augmentation techniques. These figures were measured on a natural gas-fired GT operating in an open-cycle power plant.Copyright

Compressor Design From Specification to Validation: Application of a Fast and Reliable Process

To support customer requirements for existing power plants inside the Service business Alstom did develop over the years a fast and reliable design process for compressors. This has meanwhile been proven with several engines. Besides high-end technologies, main focus is given on the interdisciplinary alignment. The application for an upgraded product for the mature fleet will be briefly shown. The blading re-design is based on Controlled Diffusion Airfoil (CDA) technology, individually optimized for every single blade row. Together with mechanically optimized thin blades this results in high compressor efficiency and surge margin. The CDA blading technology has been introduced in Alstom during 1990s. Therefore extended experience on this technology is available and has been manifested in design rules & criteria. The interdisciplinary blading concept and optimization is done with in-house 2D & 3D CFD codes for aerodynamics and FEM codes for mechanical integrity. To speed-up the design process, task-optimized tools are used for specific topics. All tools are linked into a design system and have an interface to a CAM system. Aerodynamic and FEM codes have been tuned/well-calibrated according to the past experience. A review process with experts is applied at certain milestones for technical and commercial issues. During blading design usually several disciplines are involved. This causes a challenge to organize the corresponding resources. Alstom uses a different approach: tasks are partly executed independent from the disciplines with standard tools. Nevertheless the final release stays inside the ownership of the expert discipline. This means e.g. that simplified tools are developed for pre-checks to be done by any discipline and the final check with high-end tools is done by the experts. This ensures a highly flexible and fast interdisciplinary approach. To validate the design and operation range of the upgraded compressors special attention is paid on testing. This reveals usually in a pre-test for the baseline engine and a post-test for the upgraded engine. For validation purposes a full compressor mapping under load and idle is done for both test series. Additional measurements for pressure rise inside the engine and validation of natural frequencies and stresses to certain blades is applied. The evaluation of the measurement data is used to confirm the improved compressor design and to check achievement of guaranteed performance figures. In addition the surge margin is measured to confirm that the upgraded compressor can be safely operated under all condition.Copyright