Extension of an Unsteady Hybrid Navier-Stokes/Vortex-Panel Solver to Wind Turbine Aerodynamic Simulations at Higher Yaw Angles

2014 ◽  
Author(s):  
Kensuke Suzuki ◽  
Sven Schmitz ◽  
Hua Ouyang ◽  
Jean-Jacques Chattot
Keyword(s):  
Wind Turbine ◽  
Computational Cost ◽  
Unsteady Aerodynamics ◽  
Navier Stokes ◽  
Test Case ◽  
Analysis Tool ◽  
Horizontal Axis Wind Turbine ◽  
Work Station ◽  
Lower Estimation ◽  
Free Wake

A new analysis tool, an unsteady Hybrid Navier-Stokes/Vortex model, for a horizontal axis wind turbine (HAWT) has been developed for yawed flow by coupling a prescribed wake Vortex Line Method (VLM) with an unsteady Navier-Stokes solver, and its convergence and computational cost have been studied for 10 and 20 degrees of yaw. In this study, a steady viscous solution of a hybrid method is compared in detail with a full-scale Navier-Stokes simulation as a validation. Furthermore, the unsteady hybrid solver is applied to the NREL Unsteady Aerodynamics Experiment (UAE) Phase VI rotor. A test case under 10 degrees of yaw shows that the global power output agrees well with the NREL experiment, and 10 cycles of computation require less than three days using a work station under a serial CPU simulation. The same simulation performed using a super computer is used as reference, and it is estimated that the equivalent case can be obtained about 8 times faster using the work station with the present method, while keeping the same level of accuracy, than a full-domain Navier-Stokes simulation. To treat high yaw cases, new distorted prescribed vortex sheets are modeled with the VLM code. To see the difference between the base helix and the distorted helicoidal wake, unsteady hybrid VLM/Navier-Stokes solutions are examined for selected azimuth angles, and results are contrasted to a free wake BEM and NREL experimental data. For low yaw angles, the base helix approximation agrees well with the distorted helix, and yield better prediction than a free wake model, whereas for high yaw angles of more than 30 degrees, the present distorted wake gave a lower estimation of rotor torque than the free wake solver.

Analysis of Unsteady Flows Past Horizontal Axis Wind Turbine Airfoils Based on Harmonic Balance Compressible Navier-Stokes Equations With Low-Speed Preconditioning

2011 ◽  
Author(s):  
M. Sergio Campobasso ◽  
Mohammad H. Baba-Ahmadi
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Harmonic Balance ◽  
Stokes Equations ◽  
Unsteady Aerodynamics ◽  
Horizontal Axis ◽  
Navier Stokes ◽  
Horizontal Axis Wind Turbine ◽  
Low Speed ◽  
Computational Performance

This paper presents the numerical models underlying the implementation of a novel harmonic balance compressible Navier-Stokes solver with low-speed preconditioning for wind turbine unsteady aerodynamics. The numerical integration of the harmonic balance equations is based on a multigrid iteration, and, for the first time, a numerical instability associated with the use of such an explicit approach in this context is discussed and resolved. The harmonic balance solver with low-speed preconditioning is well suited for the analyses of several unsteady periodic low-speed flows, such as those encountered in horizontal axis wind turbines. The computational performance and the accuracy of the technology being developed are assessed by computing the flow field past two sections of a wind turbine blade in yawed wind with both the time- and frequency-domain solvers. Results highlight that the harmonic balance solver can compute these periodic flows more than 10 times faster than its time-domain counterpart, and with an accuracy comparable to that of the time-domain solver.

scholarly journals Analysis of Unsteady Flows Past Horizontal Axis Wind Turbine Airfoils Based on Harmonic Balance Compressible Navier-Stokes Equations With Low-Speed Preconditioning

2012 ◽  
Vol 134 (6) ◽  
Author(s):  
M. Sergio Campobasso ◽  
Mohammad H. Baba-Ahmadi
Keyword(s):  
Wind Turbine ◽  
Time Domain ◽  
Harmonic Balance ◽  
Stokes Equations ◽  
Unsteady Aerodynamics ◽  
Horizontal Axis ◽  
Navier Stokes ◽  
Horizontal Axis Wind Turbine ◽  
Low Speed ◽  
Computational Performance

This paper presents the numerical models underlying the implementation of a novel harmonic balance compressible Navier-Stokes solver with low-speed preconditioning for wind turbine unsteady aerodynamics. The numerical integration of the harmonic balance equations is based on a multigrid iteration, and, for the first time, a numerical instability associated with the use of such an explicit approach in this context is discussed and resolved. The harmonic balance solver with low-speed preconditioning is well suited for the analyses of several unsteady periodic low-speed flows, such as those encountered in horizontal axis wind turbines. The computational performance and the accuracy of the technology being developed are assessed by computing the flow field past two sections of a wind turbine blade in yawed wind with both the time-and frequency-domain solvers. Results highlight that the harmonic balance solver can compute these periodic flows more than 10 times faster than its time-domain counterpart, and with an accuracy comparable to that of the time-domain solver.

Geometric-control formulation and averaging analysis of the unsteady aerodynamics of a wing with oscillatory controls

2021 ◽  
Vol 928 ◽  
Author(s):  
Haithem E. Taha ◽  
Laura Pla Olea ◽  
Nabil Khalifa ◽  
Cody Gonzalez ◽  
Amir S. Rezaei
Keyword(s):  
Control Theory ◽  
Stokes Equations ◽  
Unsteady Aerodynamics ◽  
Geometric Control ◽  
Navier Stokes ◽  
Analysis Tool ◽  
Geometric Control Theory ◽  
Reduced Order ◽  
Nonlinear Control Theory ◽  
Generation Mechanisms

Differential-geometric-control theory represents a mathematically elegant combination of differential geometry and control theory. Practically, it allows exploitation of nonlinear interactions between various inputs for the generation of forces in non-intuitive directions. Since its early developments in the 1970s, the geometric-control theory has not been duly exploited in the area of fluid mechanics. In this paper, we show the potential of geometric-control theory in the analysis of fluid flows, exemplifying it as a heuristic analysis tool for discovery of symmetry-breaking and unconventional force-generation mechanisms. In particular, we formulate the wing unsteady aerodynamics problem in a geometric-control framework. To achieve this goal, we develop a reduced-order model for the unsteady flow over a pitching–plunging wing that is (i) rich enough to capture the main physical aspects (e.g. nonlinearity of the flow dynamics at large angles of attack and high frequencies) and (ii) efficient and compact enough to be amenable to the analytic tools of geometric nonlinear control theory. We then combine tools from geometric-control theory and averaging to analyse the developed reduced-order dynamical model, which reveals regimes for lift and thrust enhancement mechanisms. The unsteady Reynolds-averaged Navier–Stokes equations are simulated to validate the theoretical findings and scrutinize the underlying physics behind these enhancement mechanisms.

Comparison of Wind Tunnel Airfoil Performance Data With Wind Turbine Blade Data

1992 ◽  
Vol 114 (2) ◽  
pp. 119-124 ◽  
Author(s):  
C. P. Butterfield ◽  
George Scott ◽  
Walt Musial
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Peak Power ◽  
Unsteady Aerodynamics ◽  
Leading Edge ◽  
Operating Conditions ◽  
Performance Data ◽  
Horizontal Axis Wind Turbine ◽  
Force Coefficients ◽  
Basic Fluid

Horizontal axis wind turbine (HAWT) performance is usually predicted by using wind tunnel airfoil performance data in a blade element momentum theory analysis. This analysis assumes that the rotating blade airfoils will perform as they do in the wind tunnel. However, when stall-regulated HAWT performance is measured in full-scale operation, it is common to find that peak power levels are significantly greater than those predicted. Pitch-controlled rotors experience predictable peak power levels because they do not rely on stall to regulate peak power. This has led to empirical corrections to the stall predictions. Viterna and Corrigan (1981) proposed the most popular version of this correction. But very little insight has been gained into the basic cause of this discrepancy. The National Renewable Energy Laboratory (NREL), funded by the DOE, has conducted the first phase of an experiment which is focused on understanding the basic fluid mechanics of HAWT aerodynamics. Results to date have shown that unsteady aerodynamics exist during all operating conditions and dynamic stall can exist for high yaw angle operation. Stall hysteresis occurs for even small yaw angles and delayed stall is a very persistent reality in all operating conditions. Delayed stall is indicated by a leading edge suction peak which remains attached through angles of attack (AOA) up to 30 degrees. Wind tunnel results show this peak separating from the leading edge at 18 deg AOA. The effect of this anomaly is to raise normal force coefficients and tangent force coefficients for high AOA. Increased tangent forces will directly affect HAWT performance in high wind speed operation. This report describes pressure distribution data resulting from both wind tunnel and HAWT tests. A method of bins is used to average the HAWT data which is compared to the wind tunnel data. The analysis technique and the test set-up for each test are described.

Small Horizontal Axis Wind Turbine: Analytical Blade Design and Comparison With RANS-Prediction and First Experimental Data

2013 ◽  
Author(s):  
Tom Gerhard ◽  
Michael Sturm ◽  
Thomas H. Carolus
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Wind Turbine ◽  
Horizontal Axis ◽  
Analytical Models ◽  
Power Coefficient ◽  
Analysis Tool ◽  
Computational Domain ◽  
Horizontal Axis Wind Turbine ◽  
Data Set

State-of-the-art wind turbine performance prediction is mainly based on semi-analytical models, incorporating blade element momentum (BEM) analysis and empirical models. Full numerical simulation methods can yield the performance of a wind turbine without empirical assumptions. Inherent difficulties are the large computational domain required to capture all effects of the unbounded ambient flow field and the fact that the boundary layer on the blade may be transitional. A modified turbine design method in terms of the velocity triangles, Euler’s turbine equation and BEM is developed. Lift and drag coefficients are obtained from XFOIL, an open source 2D design and analysis tool for subcritical airfoils. A 3 m diameter horizontal axis wind turbine rotor was designed and manufactured. The flow field is predicted by means of a Reynolds-averaged Navier-Stokes simulation. Two turbulence models were utilized: (i) a standard k-ω-SST model, (ii) a laminar/turbulent transition model. The manufactured turbine is placed on the rooftop of the University of Siegen. Three wind anemometers and wind direction sensors are arranged around the turbine. The torque is derived from electric power and the rotational speed via a calibrated grid-connected generator. The agreement between the analytically and CFD-predicted kinematic quantities up- and downstream of the rotor disc is quite satisfactory. However, the blade section drag to lift ratio and hence the power coefficient vary with the turbulence model chosen. Moreover, the experimentally determined power coefficient is considerably lower as predicted by all methods. However, this conclusion is somewhat preliminary since the existing experimental data set needs to be extended.

Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment

2003 ◽  
Author(s):  
Earl P. N. Duque ◽  
Michael D. Burklund ◽  
Wayne Johnson
Keyword(s):  
Experimental Data ◽  
Wind Turbine ◽  
Turbine Rotor ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Horizontal Axis Wind Turbine ◽  
Performance Predictions ◽  
Nasa Ames Research ◽  
Nrel Phase Vi ◽  
Wind Turbine Rotor

A vortex lattice code, CAMRAD II, and a Reynolds-Averaged Navier-Stoke code, OVERFLOW-D2, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80-by 120-Foot Wind Tunnel. Computations were performed for both axial as well as yawed operating conditions. Various stall delay models and dynamics stall models were used by the CAMRAD II code. Comparisons between the experimental data and computed aerodynamic loads show that the OVERFLOW-D2 code can accurately predict the power and spanwise loading of a wind turbine rotor.

scholarly journals A Modified Free Wake Vortex Ring Method for Horizontal-Axis Wind Turbines

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3900 ◽  
Author(s):  
Jing Dong ◽  
Axelle Viré ◽  
Carlos Simao Ferreira ◽  
Zhangrui Li ◽  
Gerard van Bussel
Keyword(s):  
Wind Turbine ◽  
Vortex Ring ◽  
Horizontal Axis ◽  
Wake Vortex ◽  
Horizontal Axis Wind Turbine ◽  
Vortex Model ◽  
Ring Method ◽  
Wake Model ◽  
Free Wake ◽  
Platform Motions

A modified free-wake vortex ring model is proposed to compute the dynamics of a floating horizontal-axis wind turbine, which is divided into two parts. The near wake model uses a blade bound vortex model and trailed vortex model, which is developed based on vortex filament method with straight lifting lines assumption. By contrast, the far wake model is based on the vortex ring method. The proposed model is a good compromise between accuracy and computational cost, for example when compared with more complex vortex methods. The present model is used to assess the influence of floating platform motions on the performance of a horizontal-axis wind turbine rotor. The results are validated on the 5 MW NREL rotor and compared with other aerodynamic models for the same rotor subjected to different platform motions. The results show that the proposed method is reliable. In addition, the proposed method is less time consuming and has similar accuracy when comparing with more advanced vortex based methods.

On the Parallelization of a Harmonic Balance Compressible Navier-Stokes Solver for Wind Turbine Aerodynamics

2011 ◽  
Author(s):  
Adrian Jackson ◽  
M. Sergio Campobasso ◽  
Mohammad H. Baba-Ahmadi
Keyword(s):  
Flow Field ◽  
Domain Decomposition ◽  
Wind Turbine ◽  
Time Domain ◽  
Harmonic Balance ◽  
Unsteady Aerodynamics ◽  
Time Domain Analysis ◽  
Domain Analysis ◽  
Navier Stokes ◽  
The Time Domain

The paper discusses the parallelization of a novel explicit harmonic balance Navier-Stokes solver for wind turbine unsteady aerodynamics. For large three-dimensional problems, the use of a standard MPI parallelization based on the geometric domain decomposition of the physical domain may require an excessive degree of partitioning with respect to that needed when the same aerodynamic analysis is performed with the time-domain solver. This occurrence may penalize the parallel efficiency of the harmonic balance solver due to excessive communication among MPI processes to transfer halo data. In the case of the harmonic balance analysis, the necessity of further grid partitioning may arise because the memory requirement of each block is higher than for the time-domain analysis: it is that of the time-domain analysis multiplied by a variable proportional to the number of complex harmonics used to represent the sought periodic flow field. A hybrid multi-level parallelization paradigm for explicit harmonic balance Navier-Stokes solvers is presented, which makes use of both distributed and shared memory parallelization technologies, and removes the need for further domain decomposition with respect to the case of the time-domain analysis. The discussed parallelization approaches are tested on the multigrid harmonic balance solver being developed by the authors, considering various computational configurations for the CFD analysis of the unsteady flow field past the airfoil of a wind tubine blade in yawed wind.

A Simplified Free Wake Method for Horizontal-Axis Wind Turbine Performance Prediction

1986 ◽  
Vol 108 (4) ◽  
pp. 400-406 ◽  
Author(s):  
A. A. Afjeh ◽  
T. G. Keith
Keyword(s):  
Wind Turbine ◽  
Performance Prediction ◽  
Vortex Method ◽  
Computational Effort ◽  
Horizontal Axis ◽  
Tip Vortex ◽  
Performance Parameters ◽  
Horizontal Axis Wind Turbine ◽  
Turbine Performance ◽  
Free Wake

Based on the assumption that wake geometry of a horizontal-axis wind turbine closely resembles that of a hovering helicopter, a method is presented for predicting the performance of a horizontal-axis wind turbine. A vortex method is used in which the wake is composed of an intense tip-vortex and a diffused inboard wake. Performance parameters are calculated by application of the Biot-Savart law along with the Kutta-Joukowski theorem. Predictions are shown to compare favorably with values from a more complicated full free wake analysis and with existing experimental data, but require more computational effort than an existing fast free wake method.

New Insight Into the Flow Around a Wind Turbine Airfoil Section1

2005 ◽  
Vol 127 (2) ◽  
pp. 214-222 ◽  
Author(s):  
F. Bertagnolio ◽  
N. N. Sørensen ◽  
F. Rasmussen
Keyword(s):  
Wind Turbine ◽  
Numerical Models ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Unsteady Aerodynamics ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Detached Eddy Simulation ◽  
Pitching Airfoil ◽  
Wind Turbine Airfoil

The objective of this paper is an improved understanding of the physics of the aeroelastic motion of wind turbine blades in order to improve the numerical models used for their design. Two- and three-dimensional Navier–Stokes calculations of the flow around a wind turbine airfoil using the k−ω SST and Detached Eddy Simulation (DES) turbulence models, as well as an engineering semiempirical dynamic stall model, are conducted. The computational results are compared to the experimental results that are available for both the static airfoil and the pitching airfoil. It is shown that the Navier–Stokes simulations can reproduce the main characteristic features of the flow. The DES model seems to be able to reproduce most of the details of the unsteady aerodynamics. Aerodynamic work computations indicate that a plunging motion of the airfoil can become unstable.

Sign in / Sign up

Export Citation Format

Share Document