In this paper, we investigate the accuracy and efficiency of time-accurate and nonlinear frequency-domain techniques for unsteady aerodynamic analysis. Specifically, we compare high-dimensional harmonic balance and time-accurate dual-time stepping techniques developed for unsteady fluid flow problems. Both methods use a finite volume discretization based on the Jameson-Schmidt-Turkel scheme that incorporates convergence acceleration techniques such as local time stepping, implicit residual smoothing and multigrid. The Spalart-Allmaras turbulence model with rotation correction is used to compute the turbulent viscosity in the Reynolds-Averaged Navier-Stokes equations. The time-accurate solver is also modified for Delayed Detached Eddy Simulations, which requires a minor modification to the Spalart-Allmaras turbulence model. In the harmonic balance approach, the time derivative term is approximated by a pseudo-spectral operator, which couples solutions at different sub-time levels. On the other hand, the dual-time stepping approach employs a second order backward difference approximation to model the time derivative term. To compare the time-accurate and harmonic balance methods, laminar vortex shedding over a circular cylinder, aeroelastic analysis of the Eleventh Standard configuration and turbulent trailing edge vortex shedding for the VKI turbine are investigated.
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