Numerical Analysis of Inlet Turbulence in an Airfoil Cascade

This paper investigates how unsteady inlet turbulence affects aerodynamic flow behavior and the performance of an airfoil cascade. The motivation for this work is Boundary Layer Ingesting (BLI) engine systems, which ingest airframe boundary layers to improve propulsive efficiency and reduce fuel burn. Boundary layer ingestion results in non-uniform flow at the engine inlet. While the effects of variations in stagnation pressure, stagnation temperature, and swirl are well described in the literature, the effects of turbulence intensity are less understood. We hypothesize that unsteady variations in inlet turbulence intensity will cause earlier bypass transition and reduce the amount of laminar flow on the BLI engine fan blades, relative to a non-BLI engine scenario. To explore this hypothesis, two-dimensional airfoil cascade simulations are performed using numerical Finite-Volume Method (FVM) solutions to the coupled Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations. For turbulence closure and the analysis of flow transition, we invoke the Menter Shear Stress Transport (SST) k–ω turbulence model with the Langtry–Menter Gamma–Reθ transition model, which captures bypass transition effects. The geometry of interest, representative of turbomachinery blading, is a cascade of NACA 65-(12)10 series airfoils, selected due to the availability of experimental data for validating baseline results. Aerodynamic performance trends are assessed with stagnation pressure loss, static pressure rise, and the behavior of the laminar-turbulent transition location. Preliminary steady results show agreement with experimental data and indicate that increasing inlet turbulence intensity from 1% to 5.5% doubles stagnation pressure loss and reduces static pressure rise by 29%. Transient cases of periodic inlet turbulence intensity are investigated for a range of amplitudes and frequencies. Preliminary transient results reveal unsteady variations in stagnation pressure loss and static pressure rise across the blade row but at a different frequency than that of the unsteady inlet turbulence.