Working Group Axial Compressors
The research activities of the compressor group are mainly focused on two areas of gas turbines applications: aviation and energy supply. The research topics are emerging directly from the demands of these applications. The area of aviation, on one hand, is facing a steadily increase in the volume of air traffic. On the other hand, environmental goals have been tightened under the agreement of ACARE, which states, that NOx and CO2 emissions should be reduced by 95% and 75%, respectively, by 2050. To meet these goals, an improvement in power and efficiency of aircraft engines is inevitable.
The decision to phase out nuclear power in 2011 in combination with the Renewable Energy Law means that a higher flexibility and controllability of power plants is now required in Germany. Gas turbines provide the most suitable facilities to compensate for load fluctuations from renewable energy resources. Nevertheless, this results in higher requirements for gas turbines like high part load flexibility over a broad performance range with a high efficiency.
The compressor is one of the main components of a gas turbine and generates a significant amount of total loss due to profile and secondary flow losses. Hence, improvements in the compressor directly lead to a significantly higher overall efficiency.
The compressor group endeavors to reduce aerodynamic losses by means of active and passive flow control. In terms of passive flow control, the ongoing research is focused on the aerodynamic influence of surface structures. Research activities are funded publicly.
Active Flow Control
Active flow control reduces the losses that are generated by secondary flow effects. One project deals with flow injection in the sidewall area of a stator, to decrease the extent of the corner vortex in order to increase aerodynamic stage loading. A reduction in the number of blades of up to 20% was achieved by applying a so-called "jet flap". The term "jet flap" describes an axial injection of flow along the entire blade span to take advantage of the Coanda effect.
To investigate the influence of active flow control, and to deepen the understanding of the underlying physical mechanisms a 4-stage high-speed axial compressor test rig and a cascade wind tunnel is used. To ensure highly qualitative experimental results improved measurement technologies are developed and applied. To allow the validation of the experimental results, numerical simulations are performed.
Surface structures directly affect profile losses by influencing the momentum exchange in the boundary layer. The dominating physical effect in the boundary layer depends on the type and the characteristics of the surface structure. In the context of a project the effectiveness of ideally anisotropic surface structures, so-called riblets, is experimentally investigated in the axial compressor. Riblets are tiny grooves on the surface aligned with the flow direction. Previous experimental investigations in the cascade wind tunnel showed a significant reduction of surface friction and the profile losses. The current project is a further step towards the practical application of this effect in operational use.
Operationally stressed surface structures, which are a mixture of isotropic and anisotropic surface structures, were investigated experimentally in the cascade wind tunnel. Based on the geometric and aerodynamic characterization of the surface structures a correlation for the prediction of the aerodynamic behavior was derived.
To accelerate the transfer of the knowledge gained by the experimental investigations into industrial applications, a numerical model for the prediction of the aerodynamic effect of surface structures is developed. The model is then implemented into an industrially used flow solver.
Selection of Completed Projects
- Active Flow Control in Aerodynamically Highly Loaded Compressor Stator Blades to be Applied to Jet Flaps
- Riblets on Compressor Blades - Development of Manufacturing Methods for Local Structuring and Evaluation of Loss Reduction
- Injection and Aspiration on Highly Loaded Compressor Blades
- Loss Behavior of Complex Surface Structures (CRC871)
- Riblets in a Multistage Axial Compressor
- Numerical Analysis of Cavity Flows and Sealing Systems in Axial Compressor