Hybrid RANS/LES Turbulence Model Applied to a Transitional Unsteady Boundary Layer on Wind Turbine Airfoil

Abstract

A hybrid Reynolds-averaged Navier Stokes/large-eddy simulation (RANS/LES) turbulence model integrated with a transition formulation is developed and tested on a surrogate model problem through a joint experimental and computational fluid dynamic approach. The model problem consists of a circular cylinder for generating coherent unsteadiness and a downstream airfoil in the cylinder wake. The cylinder flow is subcritical, with a Reynolds number of 64,000 based upon the cylinder diameter. The quantitative dynamics of vortex shedding and Reynolds stresses in the cylinder near wake are well captured, owing to the turbulence-resolving large eddy simulation mode that was activated in the wake. The hybrid model switched between RANS and LES modes outside the boundary layers, as expected. According to the experimental and simulation results, the airfoil encountered local flow angle variations up to ±50°. Further analysis through a phase-averaging technique found phase lags in the airfoil boundary layer along the chordwise locations, and both the phase-averaged and mean velocity profiles collapsed into the Law-of-the-wall in the range of 0 < y + < 50 . The features of high blade-loading fluctuations due to unsteadiness and transitional boundary layers are of interest in the aerodynamic studies of full-scale wind turbine blades, making the current model problem a comprehensive benchmark case for future model development and validation.

Investigating 3-D Flow Characteristics of Wind Turbine Airfoils using Delayed Detached Eddy Simulations at High Reynolds Numbers

“…The lift-to-drag ratio (L/D) of an airfoil is significantly influenced by the dynamic interaction between laminar and turbulent flow on its surface, a complex phenomenon that poses challenges for accurate prediction using computational models. The effectiveness of Hybrid RANS/LES models, incorporating a transition model, has been demonstrated in providing precise predictions of laminar separation bubbles [11] and offering valuable insights into the behavior of unsteady transitional boundary layers for wind turbine airfoils [12,13]. In the investigation of turbulence and transition models for the DU 00-W-212 wind turbine airfoil, RANS simulations were carried out using different transition models, including the e N method, γ-model, and γ-Re-θt model.…”