Optimizing Aerodynamic Efficiency and Passive Vortex Induced Vibration Suppression

1. Offshore Wind Turbine Modeling: Optimizing Aerodynamic
Efficiency and Passive Vortex Induced Vibration Suppression
Billard, William J.1
, Beibei Ren1
, Ph.D., Yeqin Wang1
, Antonio Bula2
, Ph.D.
1
Department of Mechanical Engineering, Texas Tech University
2
Department of Mechanical Engineering, Universidad del Norte
ABSTRACT
METHODS
OBJECTIVE
RESULTS
CONCLUSIONS
Wind turbines are second to hydropower in cost of producing power. Unlike onshore turbines, offshore turbines are
proven to produce more power with less of an environmental impact. Currently offshore wind turbine farms are not
prevalent in US or Colombian waters. Given the greater potential of power in deeper waters, it is imperative that an
economically viable option is engineered. The purpose of this research is to optimize the aerodynamic efficiency of
a theoretical turbine. The is efficiency is optimized through the use of XFOIL, an interactive program for the design
and analysis of subsonic isolated airfoils[5]. Also, the passive suppression of Vortex Induced Vibrations is
experimented utilizing mooring cable fairings.
ACKNOWLEDGEMENTS
As a first step, the aerodynamic efficiency of the turbine blades are to be optimized through each airfoil power
coefficient or Cp with each foil exhibiting different Cp values at varying wind speeds. The Cp curves serve
as the most important reference when distinguishing between airfoils and their potential power outputs. The
National Advisory Committee for Aeronautics (NACA) developed the airfoils to be utilized in the turbine blade
geometry. QBlade, an open source software developed by the Technical University of Berlin, is used to test the
airfoils and turbine blade.
As the second step, the Vortex Induced Vibrations (VIV) are to be suppressed passively. When flexible bodies
with bluff cross sections, pressure drag dominated, are placed within an external flow vortex shedding and unstable
vibrations are caused by the fluid’s interaction on the body. The unstable vibrations can lead to stress and fatigue
resulting in damage or failure of a structure. The VIV can be suppressed actively through complex controls or
passively by changing the geometry of the body within the flow.
1. Design and simulate a wind turbine blade in order to improve aerodynamic efficiency by maximizing the power
coefficient.
2. Examine the theoretical mooring cable wake’s decrease in turbulence contributing to vortex induced vibrations.
RESULTS
Iteration 1
The first iteration features a blade with uniform airfoil geometry
throughout its length. This blade serves as a control in order to compare
the other prototype blade configurations.
● Uniform airfoil geometry
● ~.45 power coefficient
Figure 1: Prototype Blade 1
Figure 2: Power Coefficient vs Tip Speed Ratio Curve
Figure 4: Power Coefficient vs Tip Speed Ratio Curve
Figure 3: Prototype Blade 2
Iteration 2
This iteration features various airfoil profiles that were selected based
on their experimental data. This tailored airfoil yielded a higher power
coefficient when compared to the first iteration.
● Tailored geometry
● ~.47 power coefficient
● 2.28 kW experimental production
Figure 5: Prototype Blade 3
Figure 6: Power Coefficient vs Tip Speed Ratio Curve
Figures 7 & 8: Nonlinear Line Lifting Simulation
Iteration 3
The final iteration incorporates the same blade as iteration 2
but varies in terms of chord length and twist. The twisting in
the blade is incorporated in order to optimize the angle of
attack from tip to root.
● Tailored geometry
● ~.49 power coefficient
● 2.35 kW experimental production
REFERENCES
The aerodynamic efficiency of the turbine’s blade was successfully optimized through altering the
airfoils used and twist. The airfoils were selected based on their unique characteristics exhibited at varying
wind speed. Each section of the turbine blade experienced a different incoming wind speed which required
its respective airfoil in order to perform. Twist was added throughout the blade due to each sections
optimal angle of attack varying from tip to root. With twist the angle of attack was optimized, increasing
the experimental power coefficient.
Vortex Induced Vibration can be suppressed not only passively but actively through complex and
precise mathematical models. The dynamics of floating platforms is often times computed through the use
of quasi-static analysis. Quasi-static analysis only considers the static equilibrium in the mooring cable.
Considering the hydrodynamic forces exerted on the cable by the surrounding fluid, a dynamic analysis
proves to be more accurate than quasi-static. Passively suppressing the vortex induced vibrations did not
require complex mathematical models. The VIV was proven to be suppressed through the use of mooring
cable fairings .[13] The fairings streamlined the cable’s wake which lead to a reduction in vortices.
The authors would like to acknowledge the 100K Strong in the Americas Innovation Fund, Partners of
the Americas, COLCIENCIAS - Nexo Global Colombia, Texas Tech University, and Universidad del
Norte for the support of this Research Experience as part of the proposal: Program for
Internationalization of Life-experiences, Learning and Research for Students in Engineering -
P.I.L.L.A.R.S in Engineering
[1] Hua, Jieying, Zuo, Delong, Chen, Xinzhong, & Douglas, Smith. (2016). Characterization, Modeling and
Mitigation of Vortex-induced Vibration of Slender Cylinders.
[2] Gsell, Simon. Vortex-induced vibrations of a rigid circular cylinder. PhD, Dynamique des fluides, Institut
National Polytechnique de Toulouse, 2016
[3] Postnikov, Pavlovskaia, & Wiercigroch. (2017). 2DOF CFD calibrated wake oscillator model to investigate
vortex-induced vibrations. International Journal of Mechanical Sciences, 127(C), 176-190.
[4] Zhou, Razali, Hao, & Cheng. (2011). On the study of vortex-induced vibration of a cylinder with helical
strakes. Journal of Fluids and Structures, 27(7), 903-917.
[5] XFOIL: Subsonic Airfoil Development System. (2000, December 11). Retrieved July 18, 2018, from
http://web.mit.edu/drela/Public/web/xfoil/
[6] Zhu, Yao, Ma, Zhao, & Tang. (2015). Simultaneous CFD evaluation of VIV suppression using smaller
control cylinders. Journal of Fluids and Structures, 57(C), 66-80.
[7] Bearman, P. (2011). Circular cylinder wakes and vortex-induced vibrations. Journal of Fluids and
Structures, 27(5), 648-658.
[8] Huera-Huarte, F. (2017). Suppression of vortex-induced vibration in low mass-damping circular cylinders
using wire meshes. Marine Structures, 55, 200-213.
[9] Chizfahm, Yazdi, & Eghtesad. (2018). Dynamic modeling of vortex induced vibration wind turbines.
Renewable Energy,121, 632-643.
[10] Liang, Wang, Xu, Wu, & Lin. (2018). Vortex-induced vibration and structure instability for a circular
cylinder with flexible splitter plates. Journal of Wind Engineering & Industrial Aerodynamics, 174, 200-209.
[11] Kreuzer, E., & Wilke, U. (2003). Dynamics of mooring systems in ocean engineering. Archive of Applied
Mechanics, 73(3), 270-281.
[12] Benassai, Campanile, Piscopo, Scamardella, & Benassai, G. (2014). Ultimate and accidental limit state
design for mooring systems of floating offshore wind turbines. Ocean Engineering, 92(C), 64-74.
[13] Yu, Xie, Yan, Constantinides, Oakley, & Karniadakis. (2015). Suppression of vortex-induced vibrations by
fairings: A numerical study. Journal of Fluids and Structures, 54(C), 679-700.
Figure 9: Wake Oscillator model for the cylinder moving in
transversal direction only[3]
Figure 10: Add-on devices for suppression of vortex-induced vibration of cylinders (a) helical strake; (b)
shroud; (c) axial slats; (d) streamlined fairing; (e) splitter; (f) ribboned cable; (g) pivoted guiding vane; (h)
spoiler plates. (Dalton, C., U. Houston)
Figures 11,12, & 13: Experimental VIV suppression fairngs.