High-Resolution Direct Numerical Simulations of Flow Structure and Aerodynamic Performance of Wind Turbine Airfoil at Wide Range of Reynolds Numbers

https://doi.org/10.1016/j.renene.2022.04.052

Direct numerical simulations of aerodynamic performance of wind turbine aerofoil by considering the blades active vibrations

Abstract A transition-predictive Reynolds-averaged Navier–Stokes (RANS) model is introduced as the Reynolds controlling condition to constrained large-eddy simulation (TrCLES) to improve the ability of this method to predict wall-bounded laminar–turbulent transition flows. In the TrCLES method, the constraint conditions for total Reynolds stress and heat flux are only imposed to the near-wall region in transitional and turbulent boundary layer. The newly proposed method recovers direct numerical simulation in the laminar boundary region, and retrieves the traditional large-eddy simulation method in the far-wall regions. The TrCLES method is validated in simulations of external flow around the Eppler 387 (E387) airfoil and internal flow past the ultrahigh-lift low-pressure turbine T106C cascade. The improved delayed detached-eddy simulation (IDDES) method, CLES method based on full-turbulence shear stress transport model and RANS method with a three-equation transition model are also evaluated in comparison with the available experimental and numerical data. As expected, the TrCLES method can predict laminar separation bubble and separation-induced transition process in both the E387 and T106C flows pretty well. In contrast, neither IDDES nor the original CLES can provide reasonable prediction for the laminar separation-induced transition phenomenon. The validity and fidelity of the TrCLES method are further verified by simulations of the T106C cascade flows in a wider range of exit Reynolds and Mach numbers. It is shown that the TrCLES method can not only predict the time-averaged aerodynamic quantities such as isentropic Mach number and exit kinetic energy loss very well, but also capture the laminar separation bubble and unsteady flow structures with satisfactory accuracy.

Transition-based constrained large-eddy simulation method with application to an ultrahigh-lift low-pressure turbine cascade flow

Large-eddy simulation of the influence of hairpin vortex on pressure coefficient of an operating horizontal axis wind turbine

Separation-induced transition under a low level of freestream turbulence is investigated via direct numerical simulation of flow over a low-pressure turbine cascade. The results are comprehensively analyzed in physical and Fourier spaces to elucidate the mechanisms of flow transition in the shear layer and the recirculation region of the separation bubble. It is observed that the instability process in the upstream attached boundary layer provides considerable low-frequency waves to the separated shear layer. As a result, intense nonlinear effects occur in the shear layer leading to the growth of two-dimensional waves with low to high frequencies in sequence and, eventually, giving rise to the most-amplified wave associated with the vortex-shedding frequency. Inside the recirculation region, the corresponding two-dimensional waves are induced showing the evidence for previous research on receptivity. Different from the downstream propagation of two-dimensional waves, the collision and merging of upstream- and downstream-propagating oblique waves contribute to the initiation of three-dimensional fluctuations. The subsequent three-dimensionality of the shear layer is closely associated with the growth of three fundamental oblique waves with large spanwise wavelengths. It is illustrated that these characteristic modes correspond to λ-shaped vortices and continuously developing hairpin vortex chains. 

Xiangjiang Yuan

Papers

Simulations of transition and separation past a wind-turbine airfoil near stall