Unsteady Boundary Layer Behavior due to Wake Passing Effects on Low-Speed Linear Cascade Compressor Airfoils With Single and Tandem Configurations: Part 1 - Midspan Flow

Abstract This study numerically investigates the unsteady boundary layer behavior of highly loaded compressor airfoils in single and tandem configurations, subjected to wake-passing effects in a low-speed linear cascade with contracting endwalls. The influence of periodic disturbances, generated by an upstream cylindrical wake generator, is analyzed at various flow coefficients and Strouhal numbers using unsteady numerical simulations with DLR’s CFD solver TRACE, employing a rotation-corrected k-ω turbulence model and the γReΘ transition model. Results show that both configurations exhibit wake-induced transition, with the front vane of the tandem stator behaving similarly to the single stator. However, the rear vane is primarily influenced by the wake of the cylinder convecting along the pressure side of the front vane, while the suction-side wake branch is shielded, reducing unsteady effects and boundary layer losses. Calmed regions stabilize the boundary layer and delay transition, but increased wake-induced turbulence leads to higher entropy generation and overall airfoil losses, particularly at higher bar speeds. The study confirms that low bar speeds still capture key unsteady effects, enabling reduced mechanical loading in experiments. While the URANS simulations successfully resolve characteristic boundary layer features, the results remain preliminary and serve as a foundation for comparison with high-fidelity simulations and experimental validation.