LES-based numerical prediction of the trailing edge noise in a small wind turbine airfoil at different angles of attack

Abstract

In this paper, the aerodynamic field around a FX 63-137 airfoil for four angles of attack and low Reynolds numbers was simulated with a Large Eddy Simulation (LES). Following, an acoustic analogy method was employed to calculate the airfoil trailing edge (TE) noise. In this second scheme step, the far-field acoustic pressure was predicted from the LES source terms using two different methods based on Lighthill's analogy: Curle's surface approach and Ffowcs-Williams and Hall's volumetric analogy (FW-Hall). Numerical results have been validated with hot-wire anemometry for the aerodynamic fields, thus verifying the accuracy of the CFD simulation for the prediction of noise propagation to the far field. Additionally, aeroacoustic results were validated with experimental measurements carried out in an anechoic wind tunnel using a frequency analyzer. The FW-Hall formulation shows a better agreement with the experiments, especially in the range of frequencies corresponding to the trailing edge, whereas Curle's analogy overpredicts airfoil sound. An exhaustive analysis of the aerodynamic flow field has been performed in order to better understand the generation mechanisms of the TE noise. The aeroacoustic calculations presented in this work contribute to develop a more reliable and efficient prediction methodology based on the Computational Aeroacoustics Approach (CAA).

Wall-Resolved LES Modeling of a Wind Turbine Airfoil at Different Angles of Attack

“…Note that these waves are not reaching the airfoil TE in any of the angles of attack studied, so they are not introducing tonal contributions to the noise emission propagated to the far-field. This finding has been already reported in the open literature by the authors in previous works [7].…”

“…Since the largest scales in a boundary layer are in the order of δ, and these scales are probably also apparent in the spanwise direction [26,27], the ratio δ/L z should at least be less than one [28], L z being the spanwise extent of the domain. Taking into account that the boundary layer thickness obtained from the experimental measurements is about 2% of the chord [7], the spanwise dimension of the domain was set as L z /c = 0.164, eight times larger than the maximum length scale expected to be found in the flow. Figure 2 shows a sketch with the final dimensions of the numerical domain.…”

“…Figure 5a shows a picture of the test chamber (a cross-sectional area equal to 1.0x1.2 m 2 ) where the FX airfoil has been placed in a vertical arrangement. The different experimental equipment employed to complete the measurements is listed in the figure and includes (1) dual HW probe; (2) BNC connectors; (3) Inclined manometer; (4) CTA anemometer IFA-100; (5) Acquiring card; (6) PC; (7) Anechoic chamber and (8) FX 63-137 airfoil. More details about the measuring devices can be found in [7,25].…”

“…In addition, the results obtained can be used as a starting point for the application of hybrid aeroacoustic models, in which the far-field acoustic pressure is predicted from the LES source terms using methods based on Lighthill's acoustic analogy [6]. Solís-Gallego et al [7] have applied Curle's surface approach [8] and Ffowcs-Williams and Hall's volumetric analogy (FW-Hall) [9] to predict the far-field trailing edge noise radiated by a high-lift wind turbine airfoil.…”

An optimized airfoil geometry for vertical-axis wind turbine applications

“…Biomimicry, the science that studies nature in order to inspire innovative solutions for human problems, is a source of potential ideas to improve existing systems. Examples include the bullet train Shinkansken [3], [4], based on the plunging movement of the kingfisher, or wind turbine airfoils inspired in the flippers of humpback whales [5], [6] or the wings of puffins [7]. In this work, a new airfoil shape optimized for vertical-axis wind turbine applications is proposed.…”