The Effects of Turbulent Flow Over an Airfoil on NoiseGeneration HighlightsPossible EngineeringApplications- Wind Turbine noisereduction Particular Aspects of Turbulence – The effect ofeddies generated by the turbulent flow across the air foil – Eddy generatednoiseMethodology – Numerical andexperimental peer reviewed data obtained from a literature search will be analysed.Intended Contributions- Provide a betterunderstanding of the relationship between turbulent flow and the flow inducednoise- Correlate thedegree of turbulence to the output of noise Expected Specific Results- The generation ofnoise due to turbulent flow will be greater than an airfoil exhibiting laminarflow IntroductionDue to an overwhelming demand in clean energy, a drive towards theadaption of renewables is being generated. One such method of clean electricity generation is the wind turbine,more importantly the horizontal axis wind turbine. An issue with these turbines is the generationof noise, which may negatively impact their implementation.
To generate a solution to this issue, it isimportant to understand how the problem itself is created. There are two types of noise generationacross the wind turbine: mechanical and aerodynamic1. This report will not examine the generationof mechanical noise but will instead focus on the noise generated throughaerodynamic effects, as it is the dominant of the two2. As atmospheric wind is notconstant and maintains no set flow regime, it is important to consider bothturbulent and laminar flow. It isessential to compare the effects the two will have on flow induced noise. This paper will explore the difference ofnoise generated by turbulence and laminar flow over wingsPreliminary Results To understand this phenomenon, it is important to understand the methodsby which aerodynamic noise is generated. Though there are many sources by which noise if generated across a windturbine, this research will primarily explore the noise generated of theairfoils, as they are the primary source: Figure 1Wind Interaction and Noise Generation Sources Over an Airfoil 3Figure 1 shows the movement of air over an airfoil.
The leading causes of noise due to flowingwind over an airfoil are trailing edge noise, impulsive noise, inflowturbulence sound, blade time noise, and blade tower interaction3. The majority of noise is generated bytrailing edge noise, and it is due to turbulent flow effects. As flow passes over the airfoil ittransitions from laminar to turbulent.
Trailingedge noise is created by the flow reaching a turbulent regime as it near theend of the airfoil, where eddies that are generated interact with the trailingedge. Due to it being the major sourceof disturbance purpose of this paper it to explore trailing edge noise. Recent work suggests that changing the endgeometry of the airfoil may impact the production of noise. Gill et al.
conducted work surrounding theeffect of geometry on turbulent noise generation. Current work also suggeststhat sound power reduction is proportional to the airfoil thickness, and thatit is dependent on the overall airfoil geometry4. Remaining WorkEssentially thisis a two-prong problem: one is turbulence and the other is noise. It is fundament to the work to understandboth. The publication Turbulence and Noise by Michael Carley alongwith others, will serve to provide a foundation of how noise and turbulence areinterlinked. Upon that understandingwill be built the work that will constitute this paper.
Research conducted by others in the field ofturbulence, particularly in the field of turbulence over an airfoil, will beused to understand the characteristics of turbulent flow over an airfoil. Research conducted in the field of flowinduced noise over airfoils will be used to provide an understanding of theflow induced noise phenomena. Finally,the two will be compared and the characteristics of turbulence induced noisewill be explored. Results obtained fromboth those avenues will help provide a correlation between the effectsturbulence has on the magnitude of noise generation of an airfoil. Simply put the paper will answer thefollowing questions: How is turbulent flow generated over an airfoil? Howis noise generated over an airfoil? How does turbulence affect noise generationby an airfoil? Below is a timeline onhow that work will be tackled. Time line Activity Date Progress Report 15-Jan-18 Submission of progress report 22-Jan-18 Receipt of progress report TBD Literature Review 15-Jan-18 Analysis of Review 29-Jan-18 Writing of Final Report 20-Jan-18 Submit Report for Review 20-Feb-18 Review Recommended Corrections TBD Creation of presentation 19-Mar-18 Submission of Report 19-Mar-18 Presentation TBD Expected Conclusion – Noise generation is directly proportional to thedegree of turbulence over an airfoil- Eddies generated by flow lose their energy bygenerating noiseReferences 1 H. Klug, “NOISE FROM WIND TURBINESSTANDARDS AND NOISE REDUCTION PROCEDURES H .
Klug Paper presented on the 2002 ,NOISE FROM WIND TURBINES,” Forum Acusticum, no. September, pp. 16–20,2002.2 S. Oerlemans, M. Fisher, T. Maeder, andK.
Kögler, “Reduction of Wind Turbine Noise Using Optimized Airfoils andTrailing-Edge Serrations,” AIAA J., vol. 47, no. 6, pp. 1470–1481, 2009.3 T. Renzo, “SOURCES OF WIND TURBINE NOISEAND,” Acoust. Aust.
, vol. 40, no. 1, pp. 20–27, 2012.4 J.
R. Gill, “Aerofoil Geometry Effects onTurbulence Interaction Noise noise,” no. March 2016, 2015.