How additive manufacturing facilitates gas turbine testing

With advances in additive manufacturing, testing can now be economically incorporated as early as the concept or preliminary design phases in order to reduce risk of the final design configuration not meeting requirements. Design of gas turbine compressor flow path components, especially in concept phases, has traditionally relied upon analysis-only methodologies in order to down-select the final design configuration. This final configuration is then screened for requirements validation near the end of the gated design reviews.

This article contains excerpts from the paper, "Accelerated and Improved Gas Turbine Component Design via Application of Additive Manufacturing" presented by Chris Junod, Bradley Lemke, and Douglas Willham of Siemens Energy and Martin Morris, Elliott Clarke, and Kevin Millen of Bradley University at Power Gen International 2017. 

It is not uncommon in the gas turbine designs that phenomenon related to incorrect or incomplete boundary conditions, offdesign point conditions, and/or transient effects result in component performance, functionality, or life not meeting requirements. This risk of redesign because of design requirements not being met could be reduced if testing during earlier design phases was economical and could be executed with relatively short turn times. This early testing would serve to validate analytical boundary conditions, understand and identify transient effects and ultimately help define the most meaningful final design down-select criteria.

Adopting an additive manufacturing approach for prototype creation is the ideal solution for resolving the need for an economical and rapid development test results to support the growing need for acceleration of products to market. Additive manufacturing was successfully applied to aerodynamic development testing within the preliminary design phase for boundary condition definition of new compressor static flow path components for Siemens Energy SGT-A05 industrial gas turbine engine product line.

Aerodynamic development and validation testing of gas turbine component designs are typically conducted in partial sector rigs, full scale component/sub-system rigs and/or in full engine test facilities. This approach to development testing always requires a compromise between capturing the perceived most important design features, rig/test availability, test facility capability, cost, and schedule. Depending upon the component being tested, the utilization of these various testing methods is usually determined by economics, thus requiring that testing be conducted in facilities that already exist that can be made to work.

This method is obviously not ideal and in many cases highly limits potential design improvements and introduces significant risk to the final design. Some components, like static compressor components, have traditionally been designed via analytical methods only, using a combination of one, two, and/or threedimensional analysis methods, in order to define the final design configuration from which test hardware is created. This analysis-only technique is used in all design phases before hardware is ever made available.

The final designs are at best validated in a rotating rig for compressor mapping but most often are carried directly into full engine testing for validation in order to reduce development costs. This methodology obviously increases the amount of significant risk that the final design will not meet requirements; which a resultant failure could easily result in schedule increases of more than a year and costs which could easily double.

Based upon past experience, the most frequent causes of these errors are poorly-defined boundary conditions (both aerodynamic and mechanical) and the discovery of other un-analyzed/quantified design drivers like transient dynamic effects. Lessons-learned from past compressor design experience, coupled with the high paced advancement in additive manufacturing technologies, prompted Siemens Energy to adopt AM into early design aerodynamic testing for the next generation of compressor vanes. Because of the technical complexity of these new component designs, coupled with a lack of scalable and accurate legacy test data, the need for accurate inlet boundary conditions is mandatory.