WP-3 Internal Flows—Compressors

In the case of a civil turbofan engine operating at particularly high altitudes the Reynolds number can drop by a factor of 4, when compared to the sea level values. The laminar boundary layer on the transonic compressor rotor blades interacts with shock waves and as a result a strong boundary layer separation forms. This can seriously affect the aero-engine performance and operation. One way to avoid strong separation is to ensure that the boundary layer upstream of the shock wave is turbulent. Forcing transition within the boundary layer can be achieved through the application of surface roughness patches. Although such passive control methods are already in use, the mechanism of the shock wave-laminar boundary layer interaction, and in particular the source of the strong shock unsteadiness are still not well understood. Furthermore, the benefits of boundary layer control obtained for low Reynolds numbers can turn into loss increase at the higher levels of Reynolds numbers. Another possibility of transition control is to use Vortex Generators driven by Air Jet (AJVG). In the compressor application the jets may be driven by the pressure difference between pressure and suction side of the blade. There are two effects which are present. The main effect is resulting from streamwise vortices generated on the blade suction side. The second effect is the suction of the boundary layer on the pressure side. The goal of Work Package 3 was to improve the understanding of the shock wave–laminar boundary layer interaction on the transonic compressor blade. This can potentially lead to successful new design solutions.