The by which aerodynamic noise is generated. Though

 

 

 

 

 

 

The Effects of Turbulent Flow Over an Airfoil on Noise
Generation

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Highlights

Possible Engineering
Applications

–         
Wind Turbine noise
reduction

 Particular Aspects of Turbulence

–         
The effect of
eddies generated by the turbulent flow across the air foil

–         
Eddy generated
noise

Methodology

–         
Numerical and
experimental peer reviewed data obtained from a literature search will be analysed.

Intended Contributions

–         
Provide a better
understanding of the relationship between turbulent flow and the flow induced
noise

–         
Correlate the
degree of turbulence to the output of noise

 Expected Specific Results

–         
The generation of
noise due to turbulent flow will be greater than an airfoil exhibiting laminar
flow

Introduction

Due to an overwhelming demand in clean energy, a drive towards the
adaption 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 generation
of noise, which may negatively impact their implementation.  To generate a solution to this issue, it is
important to understand how the problem itself is created.  There are two types of noise generation
across the wind turbine: mechanical and aerodynamic1.  This report will not examine the generation
of mechanical noise but will instead focus on the noise generated through
aerodynamic effects, as it is the dominant of the two2. As atmospheric wind is not
constant and maintains no set flow regime, it is important to consider both
turbulent and laminar flow.  It is
essential to compare the effects the two will have on flow induced noise.  This paper will explore the difference of
noise generated by turbulence and laminar flow over wings

Preliminary Results

To understand this phenomenon, it is important to understand the methods
by which aerodynamic noise is generated. 
Though there are many sources by which noise if generated across a wind
turbine, this research will primarily explore the noise generated of the
airfoils, as they are the primary source:

Figure 1
Wind Interaction and Noise Generation Sources Over an Airfoil 3

Figure 1 shows the movement of air over an airfoil.  The leading causes of noise due to flowing
wind over an airfoil are trailing edge noise, impulsive noise, inflow
turbulence sound, blade time noise, and blade tower interaction3.  The majority of noise is generated by
trailing edge noise, and it is due to turbulent flow effects.  As flow passes over the airfoil it
transitions from laminar to turbulent.  Trailing
edge noise is created by the flow reaching a turbulent regime as it near the
end of the airfoil, where eddies that are generated interact with the trailing
edge.  Due to it being the major source
of disturbance purpose of this paper it to explore trailing edge noise.  Recent work suggests that changing the end
geometry of the airfoil may impact the production of noise.  Gill et al. conducted work surrounding the
effect of geometry on turbulent noise generation. Current work also suggests
that sound power reduction is proportional to the airfoil thickness, and that
it is dependent on the overall airfoil geometry4. 

Remaining Work

Essentially this
is a two-prong problem: one is turbulence and the other is noise.  It is fundament to the work to understand
both.  The publication Turbulence and Noise by Michael Carley along
with others, will serve to provide a foundation of how noise and turbulence are
interlinked.  Upon that understanding
will be built the work that will constitute this paper.  Research conducted by others in the field of
turbulence, particularly in the field of turbulence over an airfoil, will be
used to understand the characteristics of turbulent flow over an airfoil.  Research conducted in the field of flow
induced noise over airfoils will be used to provide an understanding of the
flow induced noise phenomena.  Finally,
the two will be compared and the characteristics of turbulence induced noise
will be explored.  Results obtained from
both those avenues will help provide a correlation between the effects
turbulence has on the magnitude of noise generation of an airfoil.  Simply put the paper will answer the
following questions: How is turbulent flow generated over an airfoil? How
is noise generated over an airfoil? How does turbulence affect noise generation
by an airfoil?  Below is a timeline on
how 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 the
degree of turbulence over an airfoil

–         
Eddies generated by flow lose their energy by
generating noise

References

1       H. Klug, “NOISE FROM WIND TURBINES
STANDARDS 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, and
K. Kögler, “Reduction of Wind Turbine Noise Using Optimized Airfoils and
Trailing-Edge Serrations,” AIAA J., vol. 47, no. 6, pp. 1470–1481, 2009.

3       T. Renzo, “SOURCES OF WIND TURBINE NOISE
AND,” Acoust. Aust., vol. 40, no. 1, pp. 20–27, 2012.

4       J. R. Gill, “Aerofoil Geometry Effects on
Turbulence Interaction Noise noise,” no. March 2016, 2015.