31 research outputs found
Investigation of the Rotor Wake of Horizontal Axis Wind Turbine under Yawed Condition
The wake and the lack of existing velocity behind the wind turbine affect the energy production and the mechanical integrity of wind turbines downstream in the wind farms. This paper presents an investigation of the unsteady flow around a wind turbine under yawed condition. The simulations and experimental measures are made for the yaw angle rotor 30° and 0°. The wind velocity is 9.3 m/s and the rotation velocity rotor of the wind turbine in 1300, 1500 and 1800 rpm. The wind turbine rotor which is modeled is of a commercial wind turbine i.e. Rutland 503. The approach Improved Delayed Detached Eddy Simulation (IDDES) based on the SST turbulence model is used in the modeling of the flow. The solutions are obtained by using the solver which uses finite volume method. The particle image velocimetry (PIV) method is used in wind tunnel measurements in the experimental laboratory of the ENSAM Paris-Tech. The yawed downstream wake of the rotor is compared with that obtained by the experimental measurements. The results illustrate perfectly the development of the near and far wake of the rotor operation. It is observed that the upstream wind turbine yawed will have a positive impact on the power of the downstream turbine due the distance reduction of the downstream wake of the wind turbine. However the power losses are important for yawed wind turbine when compared with the wind turbine without yaw. The improved understanding of the unsteady environmental of the Horizontal Axis wind Turbine allows optimizing wind turbine structures and the number of wind turbines in wind farms
New Actuator Disk Model for the Analysis of Wind Turbines Wake Interaction with the Ground
Wake models based on Actuator Disk theory are usually applied to optimize the wind farm layouts and improve their overall efficiency and expected AEP. Despite the effectiveness of the existing models, most Actuator Disk approaches are based on the flow axisymmetric assumption, without considering the ground effect on the wake behavior. However, it has been shown that the mastâs height, or distance from the wind turbine to the ground, has an influence on the wake expansion on both hubâs side and at downstream of the wind turbine. Therefore, in this study, a hybrid CFD-BEM-Actuator Disk approach is developed to address the lack of the existing models. In the proposed model, the 3D wind rotor is modeled by a set of blade elements. Then, the local lift and drag forces acting on each blade element are calculated using BEM theory and incorporated into the momentum equation. This BEM-AD model is implemented in a User Defined Function (UDF) that is loaded into the CFD software. Thereby, ground effects are considered to be a wall boundary and defining a wind boundary layer profile at the inlet boundary, which describes the Atmospheric Boundary Layer (ABL). For the validation of this new Actuator Disk model, an enhanced experimental study is conducted at the Dynfluid Laboratory wind tunnel (ENSAM School Paris Tech). The Particle Image Velocimetry (PIV) measurements are used for the experimental wake explorations applied to a miniature two-bladed wind turbine. The wake developments are analyzed at two different hub heights ratio, h/D = 0.7 and 1.0 (where h is the hub height, and D is the wind rotor diameter). The analysis of the outcomes showed that the numerical simulations are in good correlation with the experimental measurements of the ENSAM wind tunnel. The numerical results show that for h/D=0.7, the upper half of the rotor operates within the boundary layer whereas the lower tip vortices are mainly developed in the horizontal direction with lower intensity compared to the upper tip vortices. This effect was not observed for the case h/D=1.0 where the rotor operates outside of the boundary layer; however, the wake centerline is upward deflected at about 0.3D. The main conclusion is that a distance above 7D must be observed between wind turbines to optimize the wind farm performance and over 1D hub height be required to limit the influence of the ground boundary layer effect
COUPS DE BELIER DANS UN RESEAU RAMIFIE ENTERRE EN REFOULEMENT
Un aperçu bibliographique montre que le coup de bĂ©lier engendrĂ© dans une conduite en charge a Ă©tĂ© toujours Ă©tudiĂ©, ensupposant que cette derniĂšre est libre (non enterrĂ©e). La pression externe exercĂ©e par le sol nâa pas Ă©tĂ© considĂ©rĂ©e, et parconsĂ©quent la conduite peut se dĂ©former librement dans le sens radial. Dans cette hypothĂšse, le calcul du coup de bĂ©lier nenous informe pas sur la valeur susceptible dâexister rĂ©ellement si les conduites sont soumises Ă la charge externe (sol).Dans ce travail, la mĂ©thode des caractĂ©ristiques est appliquĂ©e Ă un rĂ©seau simple ramifiĂ© de rang 2, divergent libre et enterrĂ©,en refoulement. Afin de montrer lâeffet du sol sur le coup de bĂ©lier, le raisonnement sâest portĂ© sur le cas des conduites en acieret en PVC libres et enterrĂ©es dans un sol de caractĂ©ristiques connues. Une comparaison a Ă©tĂ© prĂ©sentĂ©e sous forme de courbesmontrant ainsi la variation dans le temps des charges nodale et celle Ă la sortie de la pompe pour les deux types de matĂ©riau encas libre et enterrĂ©.Mots clĂ©s : rĂ©gime transitoire- cĂ©lĂ©ritĂ©- coup de bĂ©lier.- rĂ©seau ramifiĂ©
Unsteady loads evaluation for a wind turbine rotor
This paper presents a method for calculating the flow around a wind turbine rotor. The real flow is replaced by a free stream past a vortex model of the rotor. This model consists of lifting vortex lines which replace the blades and a trailing free vorticity. The vorticity shed from the blade is concentrated in two vortices issued from tip and root. To compute the unsteady forces exerted on the rotor, a free wake method is used. The evolution of the wake is obtained by tracking the markers representing the vortices issued from the blade tips and roots. To solve the wake governing equation and to obtain the marker positions, a time-marching method is applied and the solution is obtained by a second order predictor-corrector scheme. To validate the proposed method a comparison is made with experimental data obtained in the case of a model of wind turbine where the flow field immediately behind the rotor is measured by means of PIV. It is shown that the numerical simulation captures correctly the near wake development. The comparison shows satisfactory accuracy for the velocity field downstream of the rotor
Real Promise or False Hope: DOE's Title XVII Loan Guarantee
While the American Recovery and Reinvestment Act of 2009 expanded the DOE loan guarantee program to include certain "shovel-ready" projects, and appropriated $6 billion to cover the credit subsidy cost associated with these projects, it failed to resolve some of the most pressing problems facing the program. Here are some recommendations that may finally get some shovels in the ground.
Nano channels in the spider fang for the transport of Zn ions to cross link His rich proteins pre deposited in the cuticle matrix
AbstractWe identify the presence of multiple vascular channels within the spider fang. These channels seem to serve the transport of zinc to the tip of the fang to cross-link the protein matrix by binding to histidine residues. According to amino acid and elemental analysis of fangs extracted shortly after ecdysis, His-rich proteins are deposited before Zn is incorporated into the cuticle. Microscopic and spectroscopic investigations in the electron microscope and synchrotron radiation experiments suggest that Zn ions are transported through these channels in a liable (yet unidentified) form, and then form stable complexes upon His binding. The resulting cross-linking through the ZnâHis complexes is conferring hardness to the fang. Our observations of nano-channels serving the Zn-transport within the His-rich protein matrix of the fibre reinforced spider fang may also support recent bio-inspired attempts to design artificial polymeric vascular materials for self-healing and in-situ curing