风力叶片三维流场分析理解

4th European Conference on TURBOMACHINERY Fluid Dynamics and Thermodynamics Mach 20-23, 2001, Firenze, Italy. Pp.911-924. ATI-SCT-079/01

-1-NUMERICAL INVESTIGATION OF THE 3D

FLOW AROUND NREL UNTWISTED WIND TURBINE BLADES

Shun KANG and Charles HIRSCH

Dept. of Fluid Mechanics, Vrije Universiteit Brussel (VUB), Pleinlaan 2, 1050 Brussel, Belgium kang@stro.vub.ac.be; hirsch@stro.vub.ac.be

ABSTRACT This paper presents the numerical results of NREL Phase II HAWT blade, compared with the experimental data. An advanced Navier-Stokes solver, EURANUS/Turbo, is applied with non-linear k-ε model for closure. Comparisons with Baldwin-Lomax algebraic and linear k-ε models are also presented. The computations are performed at three different wind speeds, and excellent agreement is obtained over the range where the angle of attack of the local incoming flow is small. At higher angle of attack and large separated regions, the associated flow analysis requires time dependent computations for more detailed interpretations.

INTRODUCTION It is well known that wind flowing around a Horizontal Axial Wind Turbine (HAWT) blade is unsteady and three-dimensional. Due to the contribution of Coriolis and centrifugal forces, strong radial flows appear in the separated flow region. Aerodynamic modeling of HAWT rotors by means of the conventional "engineering methods" has reached a point where no further development can be expected without a full understanding of the flow physics. Experimental work in that direction is, however, rather limited. An alternative for providing the missing insight of rotary aerodynamics is the use of CFD techniques and state-of-art Navier-Stoke flow solvers.

Numerical simulations of HAWT rotor blades, with Navier-Stokes flow solver, by Hansen et al. [1] and Duque et al. [2, 3] have shown promise in CFD applications for predicting the rotor aerodynamic performance.

This paper presents numerical results of the three-dimensional viscous flow around the NREL Phase II HAWT blade, compared to the experimental data. The numerical results are obtained with the Navier-Stokes code EURANUS/Turbo, with non-linear k-ε model for closure. Comparisons with Baldwin-Lomax algebraic and linear k-ε models will also be presented. This work is part of the authors’ contributions to the JOULE III program called 4th European Conference on TURBOMACHINERY Fluid Dynamics and Thermodynamics Mach 20-23, 2001, Firenze, Italy. Pp.911-924. ATI-SCT-079/01

-2-Viscous and Aeroelastic Effects on Wind Turbine Blades (VISCEL)[4].

BRIEF DESCRIPTION OF NREL WIND TURBINE NREL׳s (National Renewable Energy Lab) combined experiment Phase II HAWT is a highly instrumented downwind, three-bladed machine [3, 5]. The blades, with rectangular blade planform, are untwisted and untapered. The rotor has a diameter of 10 m. The blade span (from flange to tip) is 4.521 m. The blade profile is NREL S809 with a chord of 0.46 m. The blade is pitched down by 12º. The rotor hub is fixed at a pre-cone of 3º and is mounted onto a nacelle that contains the transmission and electrical power generation equipment.

a) b) Fig.1 Computational mesh, a) near ״hub״ and blade sections (fine mesh) and b) meridional view (one level coarse mesh) 4th European Conference on TURBOMACHINERY Fluid Dynamics and Thermodynamics Mach 20-23, 2001, Firenze, Italy. Pp.911-924. ATI-SCT-079/01

-3-Three test cases, Case 1, Case 3 and Case 5, were selected for validating the code, as listed below in Table I.

Table I Definition of the Test Cases Case 1 Case 3 Case 5 Vz (m/s) 7 13 19 ω (1/s) 7.50631 7.455 7.49164 Re 3.9678E+6 7.1938E+5 7.2110E+5

The data used for validation are the static pressure distributions around the blade profile at four radial sections: 30 %, 47 %, 63 % and 80 % span.

Fig.2 Static pressure at 30, 47, 63 and 80 % span, Case 1, Vz_free = 7 m/s

63 % span 80 % span

47 % span 30 % span⊙ Exp. ----- Non-Linear k-ε - - - Linear k-ε ….. Baldwin-Lomax

X/cX/c X/c X/c4th European Conference on TURBOMACHINERY Fluid Dynamics and Thermodynamics Mach 20-23, 2001, Firenze, Italy. Pp.911-924. ATI-SCT-079/01

-4-NUMERICAL METHOD The Navier-Stokes code EURANUS, already presented in [6], solves the time-dependent Reynolds averaged Navier-Stokes equations, with either the algebraic turbulence model of Baldwin-Lomax or a two equation k-ε model for closure. It is based on a structured multiblock, multigrid approach, including non-matching block boundaries and incorporates various numerical schemes, based on either a central or an upwind discretization.