scholarly journals Prediction of the hub vortex instability in a wind turbine wake: stability analysis with eddy-viscosity models calibrated on wind tunnel data

2014 ◽  
Vol 750 ◽  
Author(s):  
F. Viola ◽  
G. V. Iungo ◽  
S. Camarri ◽  
F. Porté-Agel ◽  
F. Gallaire
Keyword(s):  
Stability Analysis ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Eddy Viscosity ◽  
General Interest ◽  
Mean Velocity ◽  
Vortex Instability ◽  
Viscosity Models ◽  
Wind Tunnel Data ◽  
The Stability

AbstractThe instability of the hub vortex observed in wind turbine wakes has recently been studied by Iungo et al. (J. Fluid Mech., vol. 737, 2013, pp. 499–526) via local stability analysis of the mean velocity field measured through wind tunnel experiments. This analysis was carried out by neglecting the effect of turbulent fluctuations on the development of the coherent perturbations. In the present paper, we perform a stability analysis taking into account the Reynolds stresses modelled by eddy-viscosity models, which are calibrated on the wind tunnel data. This new formulation for the stability analysis leads to the identification of one clear dominant mode associated with the hub vortex instability, which is the one with the largest overall downstream amplification. Moreover, this analysis also predicts accurately the frequency of the hub vortex instability observed experimentally. The proposed formulation is of general interest for the stability analysis of swirling turbulent flows.

On Application of Nonlinear k-ε Models for Internal Combustion Engine Flows

2002 ◽  
Vol 124 (3) ◽  
pp. 668-677 ◽  
Author(s):  
G. M. Bianchi ◽  
G. Cantore ◽  
P. Parmeggiani ◽  
V. Michelassi
Keyword(s):  
Internal Combustion Engine ◽  
Eddy Viscosity ◽  
Combustion Engine ◽  
Turbulence Models ◽  
Internal Combustion ◽  
Moment Closure ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
Numerical Predictions ◽  
Viscosity Models

The linear k-ε model, in its different formulations, still remains the most widely used turbulence model for the solutions of internal combustion engine (ICE) flows thanks to the use of only two scale-determining transport variables and the simple constitutive relation. This paper discusses the application of nonlinear k-ε turbulence models for internal combustion engine flows. Motivations to nonlinear eddy viscosity models use arise from the consideration that such models combine the simplicity of linear eddy-viscosity models with the predictive properties of second moment closure. In this research the nonlinear k-ε models developed by Speziale in quadratic expansion, and Craft et al. in cubic expansion, have been applied to a practical tumble flow. Comparisons between calculated and measured mean velocity components and turbulence intensity were performed for simple flow structure case. The effects of quadratic and cubic formulations on numerical predictions were investigated too, with particular emphasis on anisotropy and influence of streamline curvature on Reynolds stresses.

scholarly journals Linear stability analysis of wind turbine wakes performed on wind tunnel measurements

2013 ◽  
Vol 737 ◽  
pp. 499-526 ◽  
Author(s):  
G. V. Iungo ◽  
F. Viola ◽  
S. Camarri ◽  
F. Porté-Agel ◽  
F. Gallaire
Keyword(s):  
Stability Analysis ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Rotational Velocity ◽  
Base Flow ◽  
Wind Tunnel Measurements ◽  
Turbine Wake ◽  
Wind Turbine Wake

AbstractWind tunnel measurements were performed for the wake produced by a three-bladed wind turbine immersed in uniform flow. These tests show the presence of a vorticity structure in the near-wake region mainly oriented along the streamwise direction, which is denoted as the hub vortex. The hub vortex is characterized by oscillations with frequencies lower than that connected to the rotational velocity of the rotor, which previous works have ascribed to wake meandering. This phenomenon consists of transversal oscillations of the wind turbine wake, which might be excited by the vortex shedding from the rotor disc acting as a bluff body. In this work, temporal and spatial linear stability analyses of a wind turbine wake are performed on a base flow obtained with time-averaged wind tunnel velocity measurements. This study shows that the low-frequency spectral component detected experimentally matches the most amplified frequency of the counter-winding single-helix mode downstream of the wind turbine. Then, simultaneous hot-wire measurements confirm the presence of a helicoidal unstable mode of the hub vortex with a streamwise wavenumber roughly equal to that predicted from the linear stability analysis.

scholarly journals Wind Turbine Wake Characterization for Improvement of the Ainslie Eddy Viscosity Wake Model

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2823 ◽  
Author(s):  
Hyungyu Kim ◽  
Kwansu Kim ◽  
Carlo Bottasso ◽  
Filippo Campagnolo ◽  
Insu Paek
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Eddy Viscosity ◽  
Wind Tunnel Test ◽  
Original Model ◽  
Test Results ◽  
Wake Model ◽  
Turbine Model

This paper presents a modified version of the Ainslie eddy viscosity wake model and its accuracy by comparing it with selected exiting wake models and wind tunnel test results. The wind tunnel test was performed using a 1.9 m rotor diameter wind turbine model operating at a tip speed ratio similar to that of modern megawatt wind turbines. The control algorithms for blade pitch and generator torque used for below and above rated wind speed regions similar to those for multi-MW wind turbines were applied to the scaled wind turbine model. In order to characterize the influence of the wind turbine operating conditions on the wake, the wind turbine model was tested in both below and above rated wind speed regions at which the thrust coefficients of the rotor varied. The correction of the Ainslie eddy viscosity wake model was made by modifying the empirical equation of the original model using the wind tunnel test results with the Nelder-Mead simplex method for function minimization. The wake prediction accuracy of the modified wake model in terms of wind speed deficit was found to be improved by up to 6% compared to that of the original model. Comparisons with other existing wake models are also made in detail.

An Aerodynamic Analysis of the U.S. Brig Niagara

2007 ◽  
Author(s):  
William C. Lasher ◽  
Terrence D. Musho ◽  
Kent C. McKee ◽  
Walter Rybka
Keyword(s):  
At Risk ◽  
Stability Analysis ◽  
Wind Tunnel ◽  
Full Scale ◽  
Conventional Wisdom ◽  
Aerodynamic Forces ◽  
Wind Speeds ◽  
The Stability ◽  
The U.S ◽  
Heeling Moment

A CFD-based model has been developed for predicting the aerodynamic forces on the rig and sails of the U.S. Brig Niagara. Wind tunnel tests and full-scale experiments were performed to validate the model. The model was then used to predict both the optimum sail trim for various points of sail, as well as the heel angle for different wind speeds. The results show that the optimum bracing (or trim) angle for square sails when sailing off the wind differs significantly from conventional wisdom. The stability analysis shows that the maximum heeling moment occurs when the apparent wind is approximately 80° from the bow, and that with a typical heavy weather sail configuration Niagara would be at risk of capsize in about 40 knots of wind. These results are useful for learning about square rig sailing as well as providing guidance to the Niagara’s officers regarding survivability of the ship.

An Experimental Study of Horizontal Axis Wind Turbine Performance in Artificial Natural Wind by an Active Control Multi-Fan Turbulent Wind Tunnel

2019 ◽  
Author(s):  
Kazuhiko Toshimitsu ◽  
Hiroyuki Matsubara ◽  
Haruka Kikuchi ◽  
Porntisarn Parnravee
Keyword(s):  
Wind Tunnel ◽  
Embedded System ◽  
Wind Turbine ◽  
Power Coefficient ◽  
Inertial Subrange ◽  
Horizontal Axis Wind Turbine ◽  
Mean Velocity ◽  
Integral Scale ◽  
Turbine Performance ◽  
Natural Wind

Abstract Recent developments in wind turbine design research account for the effects of velocity fluctuation and the characteristic turbulence of the installation location site to improve performance. For the design, a low-cost natural wind generator and a laboratory-based performance evaluation of the wind turbine are useful. This paper describes a new actively controlled multi-fan wind tunnel that generates natural wind at a reduced cost. The driving section of its wind tunnel has 100 PC cooling fans that are controlled by an original embedded system. The fluctuating velocity wind is successfully generated with a mean velocity 7m/s, turbulent intensity 2% and turbulent integral scale 5 m, 10 m, 20 m, based on Karman’s power spectrum density function. In particular, the wind satisfies the Kolmogorov’s −5/3 multiplication rule of inertial subrange with the frequency range 0.01∼2.0 Hz. Furthermore, the performance of a wind turbine in steady and natural winds can be investigated. From the results, it is made clear that integral scale has a large effect on the wind turbine performance. The maximum power coefficient in natural wind of the integral scale 5 m and 10m is 124% larger than one of steady wind with the same mean velocity 7 m/s.

Development of a nonlinear eddy-viscosity closure for the triple-decomposition stability analysis of a turbulent channel

2010 ◽  
Vol 664 ◽  
pp. 74-107 ◽  
Author(s):  
V. KITSIOS ◽  
L. CORDIER ◽  
J.-P. BONNET ◽  
A. OOI ◽  
J. SORIA
Keyword(s):  
Stability Analysis ◽  
Eddy Viscosity ◽  
Turbulent Channel Flow ◽  
Decay Rates ◽  
Viscosity Model ◽  
Mode Shapes ◽  
Eddy Viscosity Model ◽  
Coherent Wave ◽  
Statistical Measures ◽  
The Stability

The analysis of the instabilities in an unsteady turbulent flow is undertaken using a triple decomposition to distinguish between the time-averaged field, a coherent wave and the remaining turbulent scales of motion. The stability properties of the coherent scale are of interest. Previous studies have relied on prescribed constants to close the equations governing the evolution of the coherent wave. Here we propose an approach where the model constants are determined only from the statistical measures of the unperturbed velocity field. Specifically, a nonlinear eddy-viscosity model is used to close the equations, and is a generalisation of earlier linear eddy-viscosity closures. Unlike previous models the proposed approach does not assume the same dissipation rate for the time- and phase-averaged fields. The proposed approach is applied to a previously published turbulent channel flow, which was harmonically perturbed by two vibrating ribbons located near the channel walls. The response of the flow was recorded at several downstream stations by phase averaging the probe measurements at the same frequency as the forcing. The experimentally measured growth rates and velocity profiles, are compared to the eigenvalues and eigenvectors resulting from the stability analysis undertaken herein. The modes recovered from the solution of the eigenvalue problem, using the nonlinear eddy-viscosity model, are shown to capture the experimentally measured spatial decay rates and mode shapes of the coherent scale.

scholarly journals Implementation of the BEM skewed-wake model within the multibody aero-elastic solver Cp-Lambda

2020 ◽  
Vol 173 ◽  
pp. 02004
Author(s):  
Igor Petrović ◽  
Filippo Campagnolo ◽  
Tadej Kosel ◽  
Carlo L. Bottasso
Keyword(s):  
Experimental Data ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Flow Conditions ◽  
Aerodynamic Loads ◽  
Model Predictions ◽  
Wind Tunnel Data ◽  
Wake Model ◽  
Nrel Phase Vi ◽  
Local Variability

To account for the problem of an azimuthally constant induction in the BEM method, which influences on incorrectly predicted aerodynamic loads in the yawed flow, a skewed-wake model implementation to the BEM method has been performed. The numerical aerodynamic loads have been compared with the wind tunnel data of the NREL Phase VI and against another numerical campaign. At first, the model predictions have been validated against experimental data performed with aligned flow conditions, showing a reasonable match. Successively, the model predictions are validated against experimental results obtained with the wind turbine yawed. Results show, a possible better prediction of loads at yawed flow with Skewed-Wake correction, however the method does not overall correlate better, compared to the BEM method with implemented local variability of the induction factor.

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