Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session E5: CFD III: LES II |
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Chair: Patrick Pisciuneri, University of Pittsburgh Room: 327 |
Sunday, November 24, 2013 4:45PM - 4:58PM |
E5.00001: Forcing of Wind Turbine Blade Boundary Layer Dynamics by Atmospheric Turbulence with Hybrid URANS-LES Ganesh Vijayakumar, Adam Lavely, Balaji Jayaraman, Brent Craven, James Brasseur We analyze spatio-temporal changes in blade boundary layer structure on a commercial-scale wind turbine blade interacting with a canonical daytime Atmospheric Boundary Layer (ABL). The time scales of the energy-containing ABL eddies are of order multiple rotations of commercial wind turbines and force large temporal fluctuations in integrated loads and bending moments. We study details of blade boundary layer dynamics underlying space-time variations in surface stress by simulating a single blade of the NREL 5MW turbine in a moderately convective ABL produced using LES from a spectral code at high resolution (147M cells). Inflow ABL boundary conditions are extracted for an OpenFOAM ABL simulation with the rotating blade. The blade boundary layer is well resolved with a new hybrid URANS-LES model that blends a 1-equation SFS stress model in the ABL with the k-$\omega$-SST-SAS model near the blade. We perform Hybrid URANS-LES computations of the flow around the blade and compute spatio-temporal fluctuations in surface stresses in response to ABL turbulence eddies. Of particular interest are sources of integrated load transients, load response time scales, and near wake temporal dynamics of vortex shedding in relationship to passage of energy containing atmospheric eddies. [Preview Abstract] |
Sunday, November 24, 2013 4:58PM - 5:11PM |
E5.00002: HPC of Loading Transients on a 5-MW Wind Turbine Rotor by Atmospheric Turbulence Eddies Adam Lavely, Ganesh Vijayakumar, Brent Craven, Balaji Jayaraman, Tarak Nandi, Eric Paterson, James Brasseur As atmospheric boundary layer (ABL) turbulence eddies sweep through a commercial wind turbine rotor disk, they generate unsteady loadings and bending moments on the blades and shafts. We use blade resolved hybrid-URANS-LES to compute unsteady loadings of a typical daytime moderately convective ABL (MCBL) on the NREL 5 MW wind turbine. The MCBL is generated with LES of exceptional resolution (147M cells) and a low-dissipation spectral algorithm. The ABL LES is used as an initial condition and as inflow boundary conditions for the NREL 5 MW computational domain. This domain is an ABL simulation with 130M cells in an OpenFOAM framework. The atmospheric eddies interact with the blades through a novel hybrid blending of the k-$\omega$-SST-SAS URANS stress model near the blade and a 1-equation SFS LES stress model in the far-field. The time variations in integrated loads, power and bending moments are being correlated with ABL eddy passage. The integrated loads will then be compared to local surface stress transients to determine the source(s) that underlie integrated load, power and moment transients. In this way, we aim to determine the role of atmospheric turbulence on deleterious blade loadings and potential relationships between loadings and local blade boundary layer dynamics. [Preview Abstract] |
Sunday, November 24, 2013 5:11PM - 5:24PM |
E5.00003: Coupling the Actuator Line and Finite Element Methods to Model Fluid Structure Interaction of a Commercial Wind Turbine in the Atmosphere Javier Motta, Pankaj Jha, Robert Campbell, Sven Schmitz, James Brasseur Wind turbine blades deform in response to unsteady loadings from atmospheric turbulence, causing changes in local angle-of-attack and blade loadings. This interaction is modeled by a fluid-structure interaction (FSI) solver that combines a finite element (FE) solver with an actuator line method (ALM) model for aerodynamic blade loads and vorticity shedding developed by Jha, et al. (2013). The FSI solver is embedded within an OpenFOAM large-eddy simulation (LES) solver for daytime atmospheric boundary layer (ABL). The flow and structure solvers are tightly coupled to ensure convergence of blade deformation and its impact on the flow field. The structural deformations are computed using a modal summation approach, where the required modal matrix and resonant frequencies are extracted using Abaqus. The ALM and FE algorithms are being optimized to provide a reasonable balance between accuracy of prediction and computation time, particularly due to the sub-iterations required for blade deformation convergence. We also aim to present an analysis of the coupling between blade loading and deformation on the NREL 5MW turbine operating in the ABL. Supported by the DOE. [Preview Abstract] |
Sunday, November 24, 2013 5:24PM - 5:37PM |
E5.00004: Large Eddy Simulation of a turbulent flow past a wind turbine placed on an undulated wall Kenneth Carrasquillo, Stefano Leonardi With the shortage of fossil fuel and increasing environmental awareness, wind turbines have become the most promising source of renewable energy. A numerical code, solving the Navier-Stokes equations, combined with immersed boundary method and line actuator model has been developed. The Immersed Boundary Method allows to model tower, nacelle and to mimic the topography without the need of body fitted grids. In the actuator line model (ALM), turbine blades are represented by a force distribution on a line which extends from the hub to the tip of the blade. A body force equal and opposite to the lift and drag is imposed in the momentum equation. This force is not imposed in one grid point, instead it is distributed in a volume surrounding the center of the element. Three cases have been considered: one with the turbine blade only, a second set of simulations includes the tower and nacelle on a flat surface and a third simulation presents an undulated wall. Periodic boundary conditions are imposed in the streamwise and spanwise directions. Preliminary results show that the topography on the ground influences the overlying turbulent flow. Roughness affects not only the mean velocity expected at the hub-height, but also fluctuations associated with coherent structures. [Preview Abstract] |
Sunday, November 24, 2013 5:37PM - 5:50PM |
E5.00005: Numerical study of the Interaction between Nonsteady Transition and Separation on Oscillating Airfoils Tarak Nandi, Balaji Jayaraman, Adam Lavely, Ganesh Vijayakumar, Eric Paterson, James Brasseur Strong correlation between vertical and horizontal turbulent motions in a daytime atmospheric boundary layer can produce $>50\%$ variability in local angle of attack(AoA) on commercial wind turbine blade sections. Lee and Gerontakos(JFM 2004)reported an unique experiment where nonsteady transition and boundary layer(BL) separation were estimated on an oscillating airfoil at $Re\sim10^5$ and reduced frequencies upto 0.2. We use the $k-\omega$ SST URANS model and the $\gamma-Re_\theta$ transition model to explore the predictive capability of these models,and to study the dynamic interactions between transition and separation on an oscillating airfoil with focus on the 3D time-dependent BL characteristics. The calculations are done in OpenFOAM on a wing section of aspect ratio 1 and periodic spanwise boundary conditions. Grid resolution analysis shows that ~6M cells are required to resolve the viscous sublayer and capture separation. Fixed AoA cases show good lift comparison but the transition model performs better at higher AoA's when separation-induced transition occurs;fully turbulent URANS mispredicts separation and lift. Prediction of the oscillating cases show differences with experiment in hysteresis loops of the force coefficients. These and related issues will be discussed. [Preview Abstract] |
Sunday, November 24, 2013 5:50PM - 6:03PM |
E5.00006: A Method for Stable Computations in the Presence of Strong Vortices at Outflow Boundaries Suchuan Dong We present a robust and accurate outflow boundary condition and an associated numerical algorithm for incompressible flow simulations on severely-truncated unbounded physical domains. This outflow boundary condition allows for the influx of kinetic energy into the domain through the outflow boundaries, and prevents un-controlled growth in the energy of the domain in such situations. The numerical algorithm for the outflow boundary condition is developed on top of a rotational velocity-correction type strategy to de-couple the pressure and velocity computations, and a special construction in the formulation prevents the numerical locking at the outflow boundaries. We show results for several flows with bounded or semi-bounded physical domains, and demonstrate that the presented method produces stable and accurate simulations on even severely truncated computational domains, where strong vortices are present at or exit the outflow boundaries. [Preview Abstract] |
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