Delayed Detached-Eddy Simulations for Separated Flows

This thesis examines the Delayed Detached-Eddy Simulation (DDES) for predicting massively separated flows around an airfoil and a flat plate at high angles of attack, comparing the results with experimental data. DDES combines Large-Eddy Simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS) simulation, with RANS used in boundary layers to reduce computational cost and LES in separated flow regions to capture large-scale turbulence.

DDES based on the Spalart-Allmaras model accurately predicted aerodynamic force coefficients, aligning well with experimental data, unlike unsteady RANS simulations which overestimated these coefficients in high-angle-of-attack flows with significant separation. Fine grid resolution in DDES revealed three-dimensional flow characteristics, indicating that longer span lengths reduce aerodynamic force fluctuations and slightly decrease time-averaged lift and drag coefficients.

Dynamic Mode Decomposition (DMD) was used to analyze the flow fields, extracting dominant dynamic modes and facilitating comparisons between computational and experimental data. DMD highlighted asymmetrical vortex shedding in the flow around a flat plate at a high angle of attack.

This thesis ultimately demonstrates the superior capability of DDES in accurately predicting complex, three-dimensional separated flows, making it a valuable tool for aerodynamic analysis.