Increasingly strict regulations regarding aircraft emissions necessitate innovative approaches to the design of aero engines that perform efficiently in different flight phases. Active flow control (AFC) is such an approach: it combines advanced technologies, such as fluid injection, aspiration and shape-variable blades, to design a compressor that aerodynamically adapts itself to the flow conditions for improved overall performance.
In order to realise such an adaptive-compressor design, it is the aim of this project to implement an AFC system that combines the targeted aspiration and injection of air with piezo-ceramically actuated blades. This will allow to manipulate the aerodynamic loading, wake flow and secondary flow to increase the attainable pressure ratio while reducing the detrimental impact of wakes and secondary-flow vortices on the efficiency.
The injection of air just upstream of the trailing edges of compressor blades adds momentum to the boundary-layer flow across the blade surface.
The additional momentum carried in the boundary layer increases the achievable turning of the flow, which leads to an improvement in the pressure rise. This allows to either increase compressor performance or to reduce the compressor weight by reducing the amount of blades and stages necessary.
Likewise, the added momentum mitigates the wake momentum deficit. The benefits of attenuated wakes are a reduction in mixing losses – resulting in increased efficiency – and a potential improvement of the aero-elastic behaviour of subsequent stages.
The aspiration of air from highly loss-afflicted flow regions, such as the secondary-flow regions at the hub and casing of the compressor, reduces the dissipation of kinetic energy into waste heat by reducing the intensity of undesirable vortices and flow separations. A greater proportion of the kinetic energy can, therefore, be converted into pressure. The result is a higher and more efficient pressure rise.
The combined application of these flow-control technologies does not just combine their benefits. Rather, it could alleviate some of the detriments associated with individual flow-control measures.
Firstly, the combination of injection and aspiration could reduce the amount of additional air necessary. If existing pressure differences can be used to drive the air flow, the system weight can be reduced significantly, as well.
Secondly, the increased flow turning achievable by means of air injection is likely to induce stronger secondary-flow vortices. Well-aimed aspiration from these flow regions would minimise the associated efficiency losses.
Lastly, to ensure efficiency and performance gains across the various phases of flight, the flow-control parameter, e.g., air-flow rates, can be adjusted depending on the actual operating conditions of the compressor.
Prof. Dr.-Ing. Joerg R. Seume
Institute of Turbomachinery and Fluid Dynamics
+49 511-762- 2733
Cluster of Excellence SE²A –
Sustainable and Energy-Efficient Aviation
Technische Universität Braunschweig
Hermann-Blenk-Str. 42
38108 Braunschweig
se2a(at)tu-braunschweig.de
+49 531 391 66661