Shock Oscillation, Loss Mechanisms and Flow Control: Recent Progress in Transonic Compressor Blade Aerodynamics

Abstract

Over the past ten years, the Institute of Propulsion Technology at the German Aerospace Center (DLR) has made significant contributions to our understanding of the mechanisms of aerodynamic loss and unsteadiness in transonic fan and compressor blades, and of how these mechanisms can be influenced. These contributions include both unique time- and space-resolved measurements in the Transonic Cascade Wind Tunnel (TGK) and unsteady numerical simulations capturing key flow phenomena. This keynote presents an integrated overview of the most relevant findings. The flow in transonic fan and compressor sections is strongly influenced by unsteady shock–boundary layer interaction (SBLI), which causes dynamic flow separation and significant losses. Time-resolved particle image velocimetry (PIV) and high-speed Schlieren imaging reveal that shock oscillations can reach 10% of the chord. Meanwhile, spectral analyses indicate aerodynamic instabilities and blade vibrations resulting from these instabilities, which are beyond the scope of steady RANS simulations. This shock buffeting also represents a particular design challenge. In the worst case, it can lead to structural failure. These effects have been mitigated by passive flow control methods and targeted aerodynamic redesigns, such as suction-side pre-compression, which have been shown to reduce shock losses without compromising operating range. Optimization confirms measurable efficiency gains. Nevertheless, a persistent discrepancy remains between RANS simulations and experiments. Accurately capturing unsteady phenomena requires high-fidelity methods (URANS and LES), which are currently too costly for routine design purposes. Integrating these insights into efficient design tools is a key future challenge.