SLE011002(1) - Wen Zhong Shen The Actuator Surface Model: A...

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Wen Zhong Shen e-mail: [email protected] Jian Hui Zhang Jens NørkAr Sørensen Department of Mechanical Engineering, Technical University of Denmark, Building 403, 2800 Lyngby, Denmark The ±ctuator Surface Model: ± New Navier–Stokes Based Model for Rotor Computations This paper presents a new numerical technique for simulating two-dimensional wind turbine Fow. The method, denoted as the 2D actuator surface technique, consists of a two-dimensional Navier–Stokes solver in which the pressure distribution is represented by body forces that are distributed along the chord of the airfoils. The distribution of body force is determined from a set of prede±ned functions that depend on angle of attack and airfoil shape. The prede±ned functions are curve ±tted using pressure distributions obtained either from viscous-inviscid interactive codes or from full Navier–Stokes simu- lations. The actuator surface technique is evaluated by computing the two-dimensional Fow past a NACA 0015 airfoil at a Reynolds number of 10 6 and an angle of attack of 10 deg and by comparing the computed streamlines with the results from a traditional Reynolds-averaged Navier–Stokes computation. In the last part, the actuator surface technique is applied to compute the Fow past a two-bladed vertical axis wind turbine equipped with NACA 0012 airfoils. Comparisons with experimental data show an en- couraging performance of the method. f DOI: 10.1115/1.3027502 g 1 Introduction For predicting wind turbine performance, there exit many dif- ferent methods. The most successful method is the classical blade element momentum s BEM d theory, which was ±rst introduced by Glauert f 1 g to predict aerodynamic loading and power. The theory is based on one-dimensional momentum theory in which the load- ing is distributed evenly in the azimuth direction, using tabulated two-dimensional airfoil data. The BEM theory has become a com- mon industrial tool for predicting wind turbine performance and is today largely used as a design tool for wind turbines. The method is ef±cient and can be run on a personal computer. Although BEM is one dimensional, it is a reliable technique in the case of con- stant axial in²ow, although it may degrade a lot in complex ²ow situations. In order to study in detail the ²ow, inviscid vortex wake meth- ods are often used for wind turbine predictions f 2–4 g . Using the technique, bound vortices are used to represent the lift on each airfoil section. The wake behind the turbine is described by using trailing and shed vortices. The induced velocity at any position is computed using Biot–Savart’s induction law, with contributions from bound vortices, tip vortices, and trailing vortices. Vortex methods can be divided into two types of models: prescribed wake models f 2 g and free wake models f 3,4 g . Prescribed wake models give fast results, whereas free wake models are more computing demanding but give more physical insight regarding the wake dynamics.
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This note was uploaded on 11/13/2011 for the course AEE 495 taught by Professor O.uzol during the Spring '11 term at Middle East Technical University.

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SLE011002(1) - Wen Zhong Shen The Actuator Surface Model: A...

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