Wind tunnel and numerical study of a small vertical axis wind turbine

A data–informed approach is presented with the objective of quantifying errors and uncertainties in the functional forms of turbulence closure models. The approach creates modeling information from higher-fidelity simulations and experimental data. Specifically, a Bayesian formalism is adopted to infer discrepancies in the source terms of transport equations. A key enabling idea is the transformation of the functional inversion procedure (which is inherently infinite-dimensional) into a finite-dimensional problem in which the distribution of the unknown function is estimated at discrete mesh locations in the computational domain. This allows for the use of an efficient adjoint-driven inversion procedure. The output of the inversion is a full-field of discrepancy that provides hitherto inaccessible modeling information. The utility of the approach is demonstrated by applying it to a number of problems including channel flow, shock-boundary layer interactions, and flows with curvature and separation. In all these cases, the posterior model correlates well with the data. Furthermore, it is shown that even if limited data (such as surface pressures) are used, the accuracy of the inferred solution is improved over the entire computational domain. The results suggest that, by directly addressing the connection between physical data and model discrepancies, the field inversion approach materially enhances the value of computational and experimental data for model improvement. The resulting information can be used by the modeler as a guiding tool to design more accurate model forms, or serve as input to machine learning algorithms to directly replace deficient modeling terms.

Using field inversion to quantify functional errors in turbulence closures

Several 2D and 3D Navier–Stokes computations performed with the compressible elsA solver, developed at ONERA, on the wind turbine tested by NREL in the NASA Ames large wind tunnel are presented. After a brief description of the tools and methods used, the predictions of the S809 aerofoil performance are first discussed. Full 3D computations are then presented, analysed and compared with the experimental results. The successes and failures of the computations are highlighted and explained. The analysis focuses in particular on the 3D and unsteady effects. Copyright © 2004 John Wiley & Sons, Ltd.

3D Navier–Stokes computations of a stall‐regulated wind turbine

*† ‡ A new correlation-based transition model has been developed, which is built strictly on local variables. As a result, the transition model is compatible with modern CFD techniques such as unstructured grids and massively parallel execution. The model is based on two transport equations, one for intermittency and one for a transition onset criterion in terms of momentum thickness Reynolds number. The proposed transport equations do not attempt to model the physics of the transition process (unlike e.g. turbulence models), but form a framework for the implementation of transition correlations into general-purpose CFD methods. The transition model was initially developed for turbomachinery and aeronautical flows. The main goal of the present paper is to validate the model for predicting transition on wind turbines. In this paper, fully turbulent and transitional computations of the 2D S809 airfoil along with a full 3D wind turbine rotor (that uses the S809 airfoil) have been accomplished. The transitional results are in good agreement with the experimental data and the transition model would appear to be well suited for the prediction of wind turbine aerodynamics.

Predicting 2D Airfoil and 3D Wind Turbine Rotor Performance using a Transition Model for General CFD Codes

Numerical study of the aerodynamic performance of a 500 W Darrieus-type vertical-axis wind turbine

Steady-state, two-dimensional CFD calculations were made for the S809 laminar-flow, wind-turbine airfoil using the commercial code CFD-ACE. Comparisons of the computed pressure and aerodynamic coefficients were made with wind tunnel data from the Delft University 1.8 m x 1.25 m low-turbulence wind tunnel. This work highlights two areas in CFD that require further investigation and development in order to enable accurate numerical simulations of flow about current generation wind-turbine airfoils: transition prediction and turbulence modeling. The results show that the laminar-to-turbulent transition point must be modeled correctly to get accurate simulations for attached flow. Calculations also show that the standard turbulence model used in most commercial CFD codes, the k-{epsilon} model, is not appropriate at angles of attack with flow separation.

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CFD calculations of S809 aerodynamic characteristics

This article describes the concept, design, implementation, and preliminary classroom experience of a computer‐based, three‐dimensional simulator for moments of inertia of uniform solid bodies. Rotation angles about each of three Cartesian axes are user‐adjustable. The moment of inertia tensor is updated in real time with any axis rotation. Simultaneously, a square‐matrix bar graph shows the relative rates of change of each tensor element. © 2000 John Wiley & Sons, Inc. Comput Appl Eng Educ 7: 221–226, 1999

3‐D simulator for moments of inertia

An adoptively refined quadtree grid method for the numerical solution of the incompressible Navier-Stokes equations is presented. A pressure-based scheme with allocated primitive variables is used as the solution algorithm. A process of grid refinement and flow solution is repeated until a sufficiently resolved solution is obtained. The present method has been applied to a variety of test cases. The results show that an adoptively refined quadtree grid can yield a better grid distribution over the flow, therefore yielding a more accurate solution as well as an improved convergence rate than a structured grid with a similar number of grid points.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=13513&context=rtd

Stuart S. Ochs

Papers

CFD calculations of S809 aerodynamic characteristics

3‐D simulator for moments of inertia

An adaptively refined quadtree grid method for incompressible flows

An adaptively-refined quadtree grid method for incompressible flows