A discussion of wind turbine interaction and stall contributions to wind farm noise

Abstract

Elsevier's Policy: An author may use the preprint for personal use, internal institutional use and for permitted scholarly posting. ... Elsevier's AAM Policy: Authors retain the right to use the accepted author manuscript for personal use, internal institutional use and for permitted scholarly posting provided that these are not for purposes of commercial use or systematic distribution. Elsevier believes that individual authors should be able to distribute their AAMs for their personal voluntary needs and interests, e.g. posting to their websites or their institution's repository, e-mailing to colleagues. However, our policies differ regarding the systematic aggregation or distribution of AAMs to ensure the sustainability of the journals to which AAMs are submitted. Therefore, deposit in, or posting to, subject-oriented or centralized repositories (such as PubMed Central), or institutional repositories with systematic posting mandates is permitted only under specific agreements between Elsevier and the repository, agency or institution, and only consistent with the publisher's policies concerning such repositories. Voluntary posting of AAMs in the arXiv subject repository is permitted. ... Highlights-Rotor-wake interaction plays a role in wind farm noise -More wake data needs to be collected -Dynamic stall noise needs to be characterised AbstractWind farms have recently been reported to produce a noise signature that is described as possessing a "thumping" quality. Measurements of these signatures are limited and their effects are debated but their effect on public opinion and complaints make them a concern for researchers in this field. Proposed reasons for these noise signatures include amplitude modulation, interference patterns and wake-rotor interaction. This paper discusses these effects and concludes that wake-rotor interaction plays a role by causing variations in turbulent-inflow noise and dynamic stall. The current state of research into stall noise and wind turbine wake structure is also reviewed and it is concluded that the available information and collected data on wind turbine wake are insufficient to determine how strong this role is. More information on the velocity and turbulence fields in the wake of horizontal-axis wind turbines as well as a characterisation of the noise produced by an airfoil experiencing dynamic stall is required in order to make a full assessment of rotor-wake contributions to wind farm noise.2

A semi-empirical airfoil stall noise model based on surface pressure measurements

“…With increasing AoA, separation rapidly propagates over the entire airfoil chord yielding an abrupt loss of lift. Furthermore, at high Reynolds numbers the vortical structures within the 20 separated flow region are unstable and the flow is turbulent. Although an important flow characteristic, airfoil stall has been less intensively studied than attached flows.…”

“…Changing the order in which integrals are performed in Eq. (20), the following three-fold integral appears as the most inner one:…”

Methods to control dynamic stall for wind turbine applications

“…Furthermore, a large hysteresis in the lift force is observed when the angles of the blade section reduces, indicating a delay in flow reattachment and lift recovery during the process. On the other hand, dynamic stall has also been observed on wind turbine blades [8e11], where it leads to increased fatigue damage accumulation at the rotor-hub joint due to large excursion in lift [12] as well as increased noise generation due to blade-vortex interaction [13]. In wind turbines, dynamic stall is caused by rapid variations of wind speed and direction [8,14,15] and is, therefore, more unpredictable compared to the rotor blades of helicopters.…”

Dynamic stall in vertical axis wind turbines: Comparing experiments and computations

“…Although dynamic stall is a dominating feature of vertical axis wind turbine flows, it has been studied extensively in many other contexts (McCroskey, 1976;Leishman and Beddoes, 1986;Carr, 1988;Geissler and Haselmeyer, 2006;Buchner et al, 2012;. On horizontal axis wind turbines, for example, even mild stall decreases performance and increases noise production significantly (Hibbs, 1986;Loratro et al, 2014), and similar effects are experienced to a greater magnitude by vertical axis turbines (Allet and Paraschivoiu, 1995;Scheurich and Brown, 2011).…”