An implementation of an aeroacoustic prediction model for broadband noise from a vertical axis wind turbine using a CFD informed methodology

Abstract

This paper presents an enhanced method for predicting aerodynamically generated broadband noise produced by a Vertical Axis Wind Turbine (VAWT). The method improves on existing work for VAWT noise prediction and incorporates recently developed airfoil noise prediction models. Inflow-turbulence and airfoil self-noise mechanisms are both considered. Airfoil noise predictions are dependent on aerodynamic input data and time dependent Computational Fluid Dynamics (CFD) calculations are carried out to solve for the aerodynamic solution. Analytical flow methods are also benchmarked against the CFD informed noise prediction results to quantify errors in the former approach. Comparisons to experimental noise measurements for an existing turbine are encouraging. A parameter study is performed and shows the sensitivity of overall noise levels to changes in inflow velocity and inflow turbulence. Noise sources are characterised and the location and mechanism of the primary sources is determined, inflow-turbulence noise is seen to be the dominant source. The use of CFD calculations is seen to improve the accuracy of noise predictions when compared to the analytic flow solution as well as showing that, for inflow-turbulence noise sources, blade generated turbulence dominates the atmospheric inflow turbulence.16m. For a VAWT with an equivalent swept area, this corresponds to any machine with a diameter of less than 5m and span of 10m.Preliminary design of SWT's almost exclusively incorporates the use of low-or reduced-order prediction tools to make early performance estimates. Popular design tools such as QBlade [2] utilise methods such as the Double-Multiple Streamtube (DMS) [3] approach for aerodynamic performance estimates. Noise estimates 15 may subsequently be made based on these preliminary flow calculations.experimental results are available [16,17]. Experimental campaigns are mostly used to study overall performance as opposed to looking at detailed flow structures. Li et al. [16] performed a thorough investigation of the flow features around the blade of a VAWT, verifying CFD calculations against wind tunnel test data and showed that CFD calculations performed well when an appropriate turbulence model was applied. There are, however, some outstanding issues to be addressed when using CFD for VAWT aerodynamic prediction [18]. 50An example of this is the matter of grid dependency such as the study by Almohammadi et al. [19] showing the sensitivity of the power/torque calculations to mesh types and the time step/Courant number.The primary objectives of the present study are concerned with the development of a validated computational method for the prediction of noise generated by a VAWT. Additionally the new methods will make use of CFD calculations as input data to existing noise models since CFD calculations can be used 55 to efficiently (and more accurately) predict detailed flow features including turbulence parameters which are important inputs required for noise prediction models. Models for inflow-turbulence and ...

A Review of Numerical Modelling of Multi-Scale Wind Turbines and Their Environment

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Effect of solidity on aeroacoustic performance of a vertical axis wind turbine using improved delayed detached eddy simulation

“…It was shown that this method could reduce the noise level up to 56%. Botha et al 20 proposed an aeroacoustic prediction model for VAWT application which was based on the CFD approach. The purpose was to find out the mechanism and location of aerodynamic noise emitted from VAWT rotor.…”

Insights into the Aeroacoustic Noise Generation for Vertical Axis Turbines in Close Proximity

“…Regarding noise, VAWTs usually have a tip speed, which is half the tip speed of horizontal axis wind turbines, and therefore are more silent [2] and can be better suited for urban turbines. Unsteady Reynolds Averages Navier-Stokes simulations have also been used to propose silent VAWTs [31], to study silent airfoils for VAWTs [32] and to derive broadband noise models [33]. In this work we retain a Large Eddy Simulation approach.…”