Computational Study of Unsteady Flows around Dragonfly and Smooth Airfoils at Low Reynolds Numbers

Gao, Haiyang; Hu, Hui; Wang, Z.J.

doi:10.2514/6.2008-385

Cited by 24 publications

(19 citation statements)

References 16 publications

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“…However, LES is compatible with a wider range of turbulent flows than RANS model, as it retains the unsteady large-scale coherent structures. For example, Cummings et al [19], Gao et al [21], and Li et al [29] proved that LES is an effective tool for simulating unsteady separated flows. The Smagorinsky-Lilly model overcomes the limitation of the original Smagorinsky sub-grid model and is one of the best-known LES models [30,31].…”

Section: Turbulence Modelsmentioning

confidence: 99%

“…The spanwise length is not fully modeled in such a 3D simulation, so that it is referred to as 2.5D CFD simulation hereinafter in order to differentiate it from the conventional 2D and 3D simulations. Gao et al [21] performed 2.5D LES simulations of the flow field around a single static airfoil and found that the 2D model is not adequate for predicting unsteady flow structures with large-scale separations around airfoils at relatively high AOAs. Furthermore, Travin et al [22], Bertagnolio et al [23], and IM and Zha [24] presented simulations of a single airfoil beyond stall using the DES method, which is essentially a hybrid model of RANS and LES.…”

Section: Introductionmentioning

confidence: 99%

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2.5D large eddy simulation of vertical axis wind turbine in consideration of high angle of attack flow

Zhu

et al. 2013

Renewable Energy

182

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A renewed interest in vertical axis wind turbines (VAWTs) has been seen recently. Computational fluid dynamics (CFD) is regarded as a promising technique for aerodynamic studies of VAWTs. In particular, 2D unsteady Reynolds-averaged Navier-Stokes (URANS) is commonly adopted, although past studies on VAWTs revealed the limited accuracy of 2D URANS. This paper investigated the feasibility and accuracy of three different CFD approaches, namely 2D URANS, 2.5D URANS and 2.5D Large Eddy Simulations (LES), in the aerodynamic characterization of straight-bladed VAWT (SBVAWT), with a focus on the capability of the 2.5D LES approach in CFD simulation of high angle of attack (AOA) flow. The 2.5D model differs from a full 3D model in that only a certain length of blades is modeled with periodic boundaries at the two extremities of the domain. The applications of these three approaches were systematically examined in the aerodynamic simulations of a single static airfoil and a 3-blade SBVAWT at different rotating speeds. Their capabilities to predict the aerodynamic forces were evaluated through a comparison with the wind tunnel results obtained by other researchers, with particular attention to high AOA flow beyond stall. Among the three methods, 2.5D LES yielded the best agreement with the experimental results in both cases. Detailed examinations of simulated flow field revealed that 2.5D LES produces more realistic 3D vortex diffusion after flow separation, resulting in more accurate predictions of aerodynamic coefficients in static or dynamic stall situations. It is noteworthy that 2.5D LES cannot capture the effect of tip vortex and vertical flow divergence in VAWTs, which used to be regarded by some researchers as the major cause of overprediction of VAWT power in 2D URANS. In this study, the considerably improved results achieved by 2.5D LES imply that the poor accuracy of URANS method is mainly due to its inherent limitation in vortex modeling. In general, 2.5D LES showed good agreement with experimental results at a relatively low tip speed ratio (TSR), but only fair agreement at a high TSR. Compared with the other two approaches, 2.5D LES is regarded as a more promising and effective CFD tool for investigating the aerodynamic characteristics of VAWTs, particularly their self-starting features corresponding to very low rotation speeds.

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Section: Turbulence Modelsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

2.5D large eddy simulation of vertical axis wind turbine in consideration of high angle of attack flow

Zhu

et al. 2013

Renewable Energy

182

View full text Add to dashboard Cite

show abstract

“…Nevertheless, LES turbulence models are suitable for a wider range of turbulent flows than RANS models. Cummings et al [44], Gao et al [45], and Li et al [46] have proved that LES turbulence models are rather effective in simulating unsteady separated flows. Meanwhile, Smagorinsky-Lilly model has conquered limitations of the original model, and become the best known LES model [47,48].…”

Section: Turbulence Models In Cfdmentioning

confidence: 97%

Darrieus vertical axis wind turbine: Basic research methods

Jin

Zhao

Ke-jun

et al. 2015

Renewable and Sustainable Energy Reviews

121

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“…At certain tip-speed ratios (TSR) namely, λ ≥ 5, the angle of attack does not exceed 12 deg. Previous researchers [3][4][5] have found that three-dimensional large-eddy simulation (LES) [6] is necessary to accurately predict the lift and drag of a stalled airfoil. At the lowest TSR (λ ≤ 1), Li et al [5] showed that three-dimensional (3-D) LES [this form of LES is sometimes called (2.5-D) LES] could accurately predict the tangential force of a straight-bladed VAWT at Re 10 5 .…”

Section: Nomenclaturementioning

confidence: 99%

Validation of a High-Order Large-Eddy Simulation Solver Using a Vertical-Axis Wind Turbine

Kanner

Persson

2016

AIAA Journal

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A high-order implicit large-eddy simulation method in two dimensions and three dimensions is used to simulate the aerodynamics of a NACA0012 airfoil over large angles of attack at low chord Reynolds numbers (Re 5000-50;000). The two-dimensional code is found to have adequate agreement with lift and drag experimental data for prestall angles of attack, whereas the three-dimensional code is validated over all angles of attack. The three-dimensional method is able to accurately predict the magnitude and frequency content of the lift and drag forces on the airfoil throughout the range of Reynolds numbers considered in this study. Further comparisons to experimental data are made, including particle image velocimetry vorticity data as well as dye-injection data. As an extension of this application, a section of a constant spinning straight-bladed vertical-axis wind turbine with two blades at a similar Reynolds number is subject to various inflow velocities in two dimensions and three dimensions. The pitch angle of the blades was also varied in order to take into account the uncertainties in the mounting angle of the blade in the experimental studies. As found previously, a small toe-out angle can increase the power absorption of the turbine on the order of 10%. The computed tangential forces as a function of the azimuthal angle agree much better with the experimental data at high tip-speed ratios as compared to other lower-fidelity analytical turbine codes.

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Computational Study of Unsteady Flows around Dragonfly and Smooth Airfoils at Low Reynolds Numbers

Cited by 24 publications

References 16 publications

2.5D large eddy simulation of vertical axis wind turbine in consideration of high angle of attack flow

2.5D large eddy simulation of vertical axis wind turbine in consideration of high angle of attack flow

Darrieus vertical axis wind turbine: Basic research methods

Validation of a High-Order Large-Eddy Simulation Solver Using a Vertical-Axis Wind Turbine

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