Wind is now the largest source of renewable energy in the United States contributing 9.7% to its total electricity production. In the year 2020, wind turbine installation in the United States surpassed 150 GW, thus capable of providing power to over 48 million houses. Consequently, it is imperative to address the shortcomings in modern day wind turbines and ensure their widespread application. One such area is the noise generated by their rotor blades, with trailing-edge noise being the dominant source.When installed closer to residential areas, studies showed that noise generated by wind turbine rotors cause annoyance and sleep disturbance to people living in its vicinity. Further studies revealed the detrimental effects of noise including impaired mental health of residents living within 0.9 miles from the installation. Therefore, wind turbine installations close to residential areas are not well accepted. Mitigating this noise would make their installation closer to residential areas possible, thus opening more avenues for wider spread of wind power applications.The preliminary step in this analysis involves accurate prediction of farfield noise propagated from the trailing-edge using Computational Aeroacoustics Analysis (CAA), which would serve as the Baseline data for comparison with noise mitigation techniques. In the present study, we have chosen a flat plate model in fully turbulent flow to demonstrate the technique.A Computational Aeroacoustics Analysis is performed on a flat plate with sharp trailing-edge for a chord-based Reynolds number of Rec = 460,000 (Uꚙ = 35 m/s). The flat plate has a circular leading-edge, which acts as a boundary layer trip and ensures that the flow is fully turbulent on its surface. A segregated flow solver (based on SIMPLE algorithm) of a commercial CFD code, STAR-CCM+ v.15.02.009, has been used to perform this study.Initially, the SST k-ω RANS turbulence model is chosen to perform steady CFD analysis. The computational domain consists of two regions: the outer fluid region on which boundary conditions are specified and the inner permeable body region which encompasses noise sources present around the flat plate. A structured mesh with hexahedral cells was created and grid refinement study was performed to ensure flowfield characteristics and noise sources present around the flat plate are well resolved for the frequency range of interest (i.e., 750 - 7000 Hz).Next, unsteady CFD analysis was performed using the SST k-ω Improved Delayed Detached Eddy Simulation. To validate our CFD results, comparisons are made with unsteady flow measurements recorded 0.6 mm downstream of the trailing-edge. It is observed that the mean velocity distribution predicted at this location matches well with the experimental data and previous computational studies. The accuracy of prediction from the present study is particularly close to the measurements near trailing-edge centerline. Further, the RMS of fluctuating velocity distribution, downstream of the trailing-edge, is comparable to predictions from previous computational studies.Noise sources around the flat plate obtained through unsteady CFD analysis are used by Farassat’s Formulation 1-A of the Ffowcs Williams and Hawkings equation to predict farfield noise propagated from the trailing-edge. The pressure fluctuation history data was collected from a point receiver located 585 mm above the trailing-edge and was converted from time domain to frequency domain using Discrete Fourier Transform. Using this information, Power Spectral Density was estimated at the receiver location.The predicted noise accurately follows the magnitude and trend of the experimental measurements for the frequency range of 750 - 7000 Hz (i.e., Strouhal number, St = 4.28 - 40.00). This trend is well predicted particularly for the frequency range from 900 - 2500 Hz (i.e., St = 5.14 - 14.28), where the trailing-edge noise is dominant.Accurate prediction of flowfield characteristics and farfield noise in the present study demonstrates the validity of this approach. Results from this study will serve as the Baseline data to assess the efficacy of the trailing-edge noise mitigation techniques in wind turbines. &nbsp;

Computational Aeroacoustics Analysis to Predict Farfield Noise From a Sharp Trailing-Edge

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.