By being exposed to atmospheric conditions gas turbines are inevitably subjected to sources of fouling. The resulting degradation can be partially recovered by cleaning the compressor. Based on open literature and patents, the different approaches leading to the most advanced method of compressor online washing have been compiled. The origins of online washing and the development trends over the decades are outlined, and the current systems are categorized. The introduction of system categories has been justified by a field survey. Additionally, the main design parameters of online washing systems are summarized.

The power and efficiency of gas turbines heavily depends on the state of the compressor. Being exposed to atmospheric conditions and pollution, fouling degrades the compressor in terms of the airflow passing and efficiency. Modern online compressor washing techniques prevent a large build up of debris by injecting washing fluid upstream of the compressor. For a satisfactory power recovery, washing methods and schemes have to be carefully adapted to the engine geometry, atmospheric and operating conditions. Therefore, the achievement of a universal cleaning procedure seems to be unlikely and only few general requirements and guidelines concerning compressor washing are available. There also is a variety of different washing systems in existence. These are either provided by the gas turbine manufacturer along with the gas turbine itself or designed by system suppliers as a retrofit for gas turbines of all makes. Based on a literature review and a patent search, a historical review of online washing systems was carried out. Different approaches and cleaning philosophies became apparent. The main influencing factors for the design of washing systems were summarized and basic categories of systems were elaborated to characterize the state-of-the-art in compressor washing equipment. A survey of installations and washing procedures used by European power plants and recommendations by major gas turbine manufacturers and system suppliers for retrofits complemented the existing data sets from the literature. The field data supported the introduced categories for online washing systems. In particular, the air/fluid ratio was shown to be a significant parameter to describe a washing system.

Online compressor washing is an advanced method to recover power losses caused by compressor blade fouling without incurring the availability penalty of having to shut down the gas turbine engine. Liquid is sprayed into the compressor at full or near full load to wash off particulates accumulated on the compressor surfaces. In particular, the cleaning of the first stage is vital to reinstate the mass flow of the engine, and a uniform fluid distribution is desirable in order to cover the full annulus. To achieve this, washing systems are generally developed empirically. Owing to the variety of intake duct geometries and gas turbine engines, the design of washing systems is generally related to individual power plants. To illustrate the trends of the main influencing parameters, a numerical investigation has been undertaken, based on an application case of a washing system installed in a heavy-duty gas turbine. The parameters studied using computational fluid dynamics (CFD) were airflow reduction, injection location and direction, droplet mass, and injection velocity. The effectiveness of the washing system was evaluated from the fluid distribution at the compressor inlet plane. It has been shown that, depending on the spray nozzle location, different optimum droplet sizes and injection velocities are required. Consequently, the application of different nozzle types is advisable. The operating condition of the engine has a significant effect on the fluid distribution at the compressor inlet and therefore changes in engine mass flow have to be considered when deciding on a washing scheme.

The design of modern aircraft engines increasingly involves highly sophisticated methodologies to match the current development pace. International company relations affect the collaboration between design offices all around the world. An important part of academic mission of modern engineering education is to produce graduates with skills compatible with industrial needs. Education may readjust accordingly to meet the higher requirements. However, a realistic scenario of the design process of an aircraft engine cannot possibly be transferred one-to-one into the student education process. A unique attempt to overcome this discrepancy was the International Gas Turbine Project. Within this project, undergraduate students have designed the cooling system of the HPT blades for a 30,000 lb thrust two-spool turbofan aeroengine. This project was collaboration between the Jet Propulsion Laboratory of TU Berlin, the Turbomachinery Group of EC Lyon and the Turbomachinery Laboratory of ETH Zurich. It also involved mentoring industry professionals from Rolls-Royce Deutschland, MTU, SNECMA and Alstom Power. Similar to modern aeroengine company structures, the design tasks included multi-component, multi-disciplinary and international interfaces of different educational systems. The student teams considered various aerothermodynamic and mechanical integrity aspects of the design. Particular attention was paid to design of the compressor, the secondary air system and the HP turbine including blade cooling. The three Universities integrated the project differently into their education curriculum and approached the tasks with different levels of software involvement. In this paper, the technical details of the design process, and the different approaches adopted are presented. Besides the application of turbomachinery-related knowledge, the impact of student interactions on the technical aspects of the project is discussed. The interfaces, including information management and the involvement of industrial partners are also addressed. Team spirit developed between the students from an initial competitive behavior to a final feeling of sitting in the same boat. It was observed that increased effort was required from academic staff in comparison to the conventional academic instruction. Nevertheless, students greatly benefited from the social interaction and an early training-on-the-job tuned to current industrial needs.

The improvement of performance simulation for gas turbines has been approached in very different ways. In particular for high bypass turbofans, efforts have been made to investigate radial flow distributions. The aim of the presented study was to combine a conventional characteristics based performance code using a 2d representation of the fan with 2d representations of the adjoining intake and bypass system. Computational Fluid Dynamics was the chosen tool to generate modules for the intake, bypass duct and bypass nozzle. This approach required geometry data. A design procedure to generate these components in an axi-symmetric meridional fashion and the numerical requirements for the CFD modules were developed. Typical component performances were predicted and the combined use of CFD and the performance code showed that in terms of performance, the inclusion of intake and bypass losses and the radial inlet distribution was worth considering. In particular however, the required numerical effort was significant.