本研究運用IEC模型以及限制性隨機模擬兩種陣風模型，探討陣風效應以及風速擾動等兩種效應，然後將其定義為風速變化趨勢以及紊流強度兩種陣風特性參數，分別取兩種不同的數值做為限制性隨機模擬法的參數，產生四組NewGust的暫態速度分佈，再加上IEC國際規範的陣風模型，總共五組暫態速度分佈做為入口流速進行暫態CFD模擬計算。
從模擬結果的分析中發現在不同暫態速度分佈之下，風機的轉子推力、扭矩以及機械功率大致上與入口風速呈正相關；而在風速達到最大值的時間點，IEC gust的轉子推力和扭矩皆比NewGust還大，而在固定風速變化趨勢急遽、紊流強度改變的情況下比較NewGust時，可看出在陣風變化趨勢急遽之下，紊流強度提高能提升轉子推力以及扭矩；在陣風的風速變化趨勢平緩時，紊流強度增加會造成轉子推力及扭矩降低。不同陣風模型的暫態速度分佈在20.125秒及20.25秒(風速最大值)時，由壓力係數可看出葉片上30%、60%、90%比例位置的翼剖面上表面部分均無發生邊界層狀態的改變；速度急遽上升的暫態效應將造成翼剖面負壓力係數突然下降非常多。而由時間平均的升力係數與阻力係數可發現Ten為65%的NewGust的平均升力係數皆為最大，而Ten為17%的NewGust的平均升力係數則皆為最小；提高紊流強度後，可發現平均阻力係數均提高。陣風對於機艙及塔架的暫態負載方向影響比葉片還大，此負載方向不斷改變的狀態將使機艙與塔架產生比穩定風速更大的疲勞損壞可能性。在流線下游處0.5DR和1DR長度位置的風速分佈在風機轉子所在高度的風速降低(Velocity deficit)較高；到流線下游處2DR長度位置之後，風速降低現象已經愈來愈低。在流線下游處1DR~1.5DR長度位置，出現平均紊流強度變化梯度的最大值，即尾流的渦流結構在此區域中崩潰(Breakdown)，因此可推斷風機位置至流線下游處1DR長度位置為近尾流(Near wake)，而流線下游處1.5DR長度位置之後則是遠尾流(Far wake)。

SUMMARY
The effects of gust and turbulence on wind turbines are discussed using IEC model and constrained stochastic simulation. The transient effects of gust are characterized as two parameters, tendency and turbulence intensity. Choosing some sets of tendency and turbulence intensity, generate four different transient velocity series, called NewGust. Including IEC gust, there are five transient velocity series as inlet boundary conditions of wind tunnel in CFD simulation.
From results of simulations, the thrust, torque, and mechanical power of rotor are similar to transient inlet velocity series. By observing pressure coefficients on blade surface, as wind velocity comes to maximum, there is no change in boundary layer state on the blade surfaces of location 30%,60%,90%. Compared with different NewGust, the higher Ten, the higher time-averaged lift coefficients. And time-averaged drag coefficients increase when TI increases in all kinds of transient inlet velocity series. According to transient loadings of the wind turbine parts, the effects of gust and turbulence on nacelle and tower are more dominant than those on blades. It is showed that the velocity deficit is higher at downstream distance 0.5DR and 1DR behind wind turbine. And the velocity deficit decrease dramatically at downstream distance 2DR. The largest difference in averaged TI occurs at downstream distance 1DR ~1.5DR , it is showed that the vortex structure breakdown at this region.

INTRODUCTION
In order to design more efficient and high stability wind turbines, the Aerodynamics simulation of wind turbine is the important topic. Currently, the large -scale wind turbines is the main tendency of wind energy development. From some articles, CFD simulation of wind turbines is almost for the small-scale wind turbines. However, there are few research of CFD simulation for the large-scale wind turbines. And there no research about gust effects on large-scale wind turbines. In view of this, the effects of gust and turbulence on large-scale wind turbines are discussed using CFD simulation.

MATERIALS AND METHODS
The transient effects of gust are characterized as two parameters, tendency and turbulence intensity. Choosing some sets of tendency and turbulence intensity, generate four different transient velocity series, called NewGust. Including IEC gust, there are five transient velocity series as inlet boundary conditions of wind tunnel in CFD simulation. From pressure and velocity field, the loading and performance of wind turbines in transient velocity series can be calculated. Next, the flow character and transient loading series can do more analysis.

RESULTS AND DISCUSSION
From results of simulations, the thrust, torque, and mechanical power of rotor are similar to transient inlet velocity series. As wind velocity comes to maximum, the thrust and torque of rotor in IEC gust are higher than those in NewGust. As Ten is 17%, TI increasing, the thrust and torque of rotor increase. However, As Ten is 65%, TI increasing, the thrust and torque of rotor decrease. By observing pressure coefficients on blade surface, as wind velocity comes to maximum, there is no change in boundary layer state on the blade surfaces of location 30%,60%,90%. Because of transient effect of wind velocity rapidly increasing, the negative pressure coefficients of blade surface decrease suddenly. Compared with different NewGust, the higher Ten, the higher time-averaged lift coefficients. And time-averaged drag coefficients increase when TI increases in all kinds of transient inlet velocity series.
According to transient loadings of the wind turbine parts, the effects of gust and turbulence on nacelle and tower are more dominant than those on blades. The direction of loading frequently changes with time, which cause more fatigue damages on structure compared with steady wind condition. It is showed that the velocity deficit is higher at downstream distance 0.5DR and 1DR behind wind turbine. And the velocity deficit decrease dramatically at downstream distance 2DR. The largest difference in averaged TI occurs at downstream distance 1DR ~1.5DR , it is showed that the vortex structure breakdown at this region. Consequently, the wake of the region from wind turbine to downstream distance 1DR is classify as near wake. And the wake of the region behind downstream distance 1.5DR is classify as far wake.

CONCLUSION
As Ten is 17%, TI increasing, the thrust and torque of rotor increase. However, As Ten is 65%, TI increasing, the thrust and torque of rotor decrease. Because of transient effect of wind velocity rapidly increasing, the negative pressure coefficients of blade surface decrease suddenly. Compared with different NewGust, the higher Ten, the higher time-averaged lift coefficients. And time-averaged drag coefficients increase when TI increases in all kinds of transient inlet velocity series. According to transient loadings of the wind turbine parts, the effects of gust and turbulence on nacelle and tower are more dominant than those on blades. The direction of loading frequently changes with time, which cause more fatigue damages on structure compared with steady wind condition. Consequently, the wake of the region from wind turbine to downstream distance 1DR is classify as near wake. And the wake of the region behind downstream distance 1.5DR is classify as far wake.

[1] H. Glauert, “Airplane propellers”, Durand WF, Aerodynamic theory, New York: Dover Publications, 1963.
[2] W.Z. Shen, R. Mikkelsen, J.N. Sørensen, and C. Bak,“Tip loss corrections for wind turbine computations”, Wind Energy,8,pp.457-75, 2005.
[3] J.G. Leishman,“A semi-empirical model for dynamic stall”, Journal of the American Helicopter Society,34,pp.3-17,1989.
[4] R.B. Langtry, J. Gola, F.R. Menter,“Predicting 2D airfoil and 3D wind turbine rotor performance using a transition model for general CFD codes”, AIAA aerospace sciences meeting and exhibit, Reno, Nevada, 44,2006.
[5] J. Whale, C.J. Fisichella, S. Selig,“Correcting inflow measurements from Hawts using a lifting-surface code”, Proceedings ASME wind energy symposium,pp.175-85,1999.
[6] J.L. Hess, “Review of integral-equation techniques for solving potential flow problems with emphasis on the surface-source method”, Computer Methods in Applied Mechanics and Engineering, 5,pp.145-96,1975.
[7] M.T. Landahl, V.J.E. Stark, “Numerical lifting-surface theory-problems and progress”, AIAA Journal,6,pp.2049-60,1977.
[8] R.D. Preuss, L. Morino, E.O. Suciu, “Unsteady potential aerodynamics of rotors with applications to horizontal-axis windmills”, AIAA Journal,18,pp.385-93,1980.
[9] J. Johansen, N.N. Sørensen, J.A. Michelsen, S. Schreck, “Detached-eddy simulation of flow around the NREL phase VI blade”, Wind Energy , 5,pp.185-97,2002.
[10] L.J. Fingersh, D. Sinuns, M. Hand, D. Jager, J. Cotrell, M. Robinson, et al, “Wind tunnel testing of NREL’s unsteady aerodynamics experiment”, Proceedings ASME wind energy symposium,pp.129-35,2001.
[11] M.M. Hand, D.A. Simms, L.J. Fingersh, D.W. Jager, J.R. Cotrell, S. Schreck, et al, “Unsteady aerodynamics experiment phase VI: wind tunnel test configurations and available data campaigns”, National Renewable Energy Laboratory, NREL/TP-500-29955, 2001.
[12] N. Sezer-Uzol, L. Long, “3-D time-accurate CFD simulations of wind turbine rotor flow fields”, AIAA aerospace sciences meeting and exhibit, Reno, Nevada, 44,2006.
[13] N.N. Sørensen, J.A. Michelsen, S. Schreck, “Navier-Stokes predictions of the NREL phase VI rotor in the NASA Ames 80 ft *120 ft wind tunnel”, Wind Energy, 5,pp.151-69,2002.
[14] E.P.N. Duque, M.D. Burklund, W. Johnson, “Navier-Stokes and comprehensive analysis performance predictions of the NREL phase VI experiment”, Journal of Solar Energy Engineering, 125,pp.457-67,2003.
[15] M.A. Potsdam, D.J. Mavriplis, “Unstructured mesh CFD aerodynamic analysis of the NREL phase VI rotor”, AIAA aerospace sciences meeting including the New Horizons Forum and aerospace exposition, Orlando, Florida, 47,2009.
[16] E. Ferrer, X. Munduate, “Wind turbine blade tip comparison using CFD”, Journal of Physics: Conference Series ,75,2007.
[17] T.M. Fletcher, R.E. Brown, “Simulation of wind turbine wake interaction using the vorticity transport model”,Wind Energy, 13, pp.587–602, 2010.
[18] Y. Li, K.J. Paik, T. Xing, P.M. Carrica, “Dynamic overset CFD simulations of wind turbine aerodynamics”, Renewable Energy, 37, pp.285-98, 2012.
[19] J.O. Mo, A. Choudhry, M. Arjomandi, R. Kelso, Y.H. Lee, “Effects of wind speed changes on wake instability of a wind turbine in a virtual wind tunnel using large eddy simulation”, J. Wind Eng. Ind. Aerodyn, 117, pp.38–56, 2013.
[20] H.J.T. Kooijman, C. Lindenburg, D. Winkelaar, and E.L. van der Hooft, “DOWEC 6 MW Pre-Design: Aero-elastic modeling of the DOWEC 6 MW pre-design in PHATAS” , ECN-CX--01-135, DOWEC 10046_009, Petten, the Netherlands: Energy Research Center of the Netherlands, 2003.
[21] C. Lindenburg, “Aeroelastic Modelling of the LMH64-5 Blade,” DOWEC-02-KL-083/0, DOWEC 10083_001, Petten, the Netherlands: Energy Research Center of the Netherlands, 2002.
[22] The UpWind Project, http://www.upwind.eu .
[23] J. Jonkman, S. Butterfield, W. Musial, G. Scott, “Definition of a 5-MW reference wind turbine for offshore system development”, National Renewable Energy Laboratory, 2009.
[24] M.C. Hsu, I. Akkerman, Y. Bazilevs, “Wind turbine aerodynamics using ALE–VMS: validation and the role of weakly enforced boundary conditions”, Comput Mech , 50, pp.499–511, 2012.
[25] Y. Bazilevs, M.C. Hsu, J. Kiendl, R. Wüchner and K.U. Bletzinger, “3D simulation of wind turbine rotors at full scale. Part I: geometry modeling and aerodynamics”, International Journal for Numerical Methods in Fluids, 2010.
[26] Y. Bazilevs, M.C. Hsu, J. Kiendl, R. Wüchner and K.U. Bletzinger, “3D simulation of wind turbine rotors at full scale. Part II: Fluid–structure interaction modeling with composite blades”, International Journal for Numerical Methods in Fluids, 2010.
[27] Y. Bazilevs, M.C. Hsu, J. Kiendl and D.J. Benson,“A computational procedure for prebending of wind turbine blades”, Int. J. Numer. Meth. Engng, 89, pp.323–336, 2012.
[28] K. Takizawa, B. Henicke, D. Montes, T.E. Tezduyar, M.C. Hsu, and Y. Bazilevs,“Numerical-performance studies for the stabilized space–time computation of wind-turbine rotor aerodynamics”, Comput Mech, 48, pp.647–657,2011.
[29] B. Hillmer, T. Borstelmann, P.A. Schaffarczyk and L. Dannenberg,“Aerodynamic and Structural Design of MultiMW Wind Turbine Blades beyond 5MW”, Journal of Physics,75, 2007.
[30] D.T. Griffith and T.D. Ashwill, “The Sandia 100-meter All-glass Baseline Wind Turbine Blade: SNL100-00”, Sandia National Laboratories, Sandia Report, 2011.
[31] K.S. Hansen, R.J. Barthelmie, L.E. Jensen, and A. Sommer, “The impact of turbulence intensity and atmospheric stability on power deficits due to wind turbine wakes at Horns Rev wind farm”, Wind Energy, 15, pp.183–96,2012.
[32] J. Meyers and C. Meneveau, “Optimal turbine spacing in fully developed wind farm boundary layers”, Wind Energy, 15, pp.305–17,2012.
[33] J.F. Manwell, J,G. McGowan and A.L. Rogers, “Wind Energy Explained Theory, Design and Application” , John Wiley & Sons Ltd, 2002.
[34] T. Burton, D. Sharpe, N. Jenkins, E. Bossanyi, “Wind Energy Handbook”, John Wiley & Sons Ltd, 2001.
[35] IEC 61400-1, Ed.3, “Wind Turbines-Part 1: Design requirements”, 2005.
[36] W. Bierbooms, “Constrained stochastic simulation—generation of time series around some specific event in a normal process”, Extremes, 8, pp.207–24, 2006.
[37] W. Bierbooms, J. Dragt, and H. Cleijne, “ Verication of the mean shape of extreme gusts”, Wind energy, 2, pp.137-50 , 1999.
[38] G. Larsen, W. Bierbooms, and K. Hansen, “ Mean gust shapes”, Riso national laboratory, Riso-R-1133(EN), 2003.
[39] E. Branlard, “ Wind energy: on the statistics of gusts and their propagation through a wind farm”, Technical report, ECN-Wind-Memo- 09-005, 2009.
[40] A.K. de Wit, “Validation of NewGust”, Delft University of Technology, SET 3901 - Graduation project, 2010.
[41] W.A. Timmer, R.P.J.O.M. van Rooij, “Summary of the Delft University Wind Turbine Dedicated Airfoils”, Delft University Wind Energy Research Institute , 2003.
[42] H. Cao, “Aerodynamics Analysis of Small Horizontal Axis Wind Turbine Blades by Using 2D and 3D CFD Modelling”, University of the Central Lancashire ,2011.
[43] “彰濱工業區設置風力發電機開發計畫環境影響說明書”, 英華威風力發電股分有限公司, 經濟部工業局, 中華民國九十四年五月。
[44] 劉瑞弘,“國際風力機設計需求-颱風參數制定現況”, 工業技術研究院 綠能與環境研究所,台灣風能學術研討會, 2013。
[45] CFX-Intro_14.0_L07_Turbulence, ANSYS, Inc, 2011.
[46] J. Smagorinsky, “General circulation experiments with the primitive equations 1: The basic experiment”, Monthly Weather Review, 91, pp.99–164 , 1963.
[47] O. Reynolds, “On the Dynamical Theory of Incompressible Viscous Fluids and the Determination of the Criterion”,Philosophical Transactions of the Royal Society of London, pp.123-64 , 1895.
[48] P. Sagaut, “Large Eddy Simulation for Incompressible Flows”, Springer, 2006.
[49] J. Hinze, “Turbulence”, McGraw-Hill,NewYork, , 2nd edn,1975.
[50] B. Vreman, B. Geurts, H. Kuerten, “Subgrid-modelling in LES of compressible flow”, Applied Scientific Research ,45,3,pp. 191–203,1995.
[51] D. Lilly, “A proposed modification of the Germano subgrid‐scale closure method”, Physics of Fluids A: Fluid Dynamics ,4, pp.633, 1992.
[52] M. Germano, U. Piomelli, P. Moin, W.H. Cabot, “A dynamic subgrid‐scale eddy viscosity model”, Physics of Fluids A: Fluid Dynamics,3, pp.1760,1991.
[53] S.E. Kim, “Large Eddy Simulation Using Unstructured Meshes and Dynamic Subgrid-Scale Turbulence Models”, Technical Report AIAA, In: Pro-ceedings of 34th Fluid Dynamics Conference and Exhibit American Institute of Aeronautics and Astronautics,2004.
[54] S.J. Schreck, N.N. Sørensen, M.C. Robinson,“Aerodynamic Structures and Processes in Rotationally Augmented Flow Fields”, Wind Energy, 10, pp.159–78,2007.
[55] L.J. Vermeer, J.N. Sørensen, A. Crespo, “Wind turbine wake aerodynamics”, Progress in Aerospace Sciences, 39, pp.467–510,2003.
[56] B. Sanderse,“Aerodynamics of Wind Turbine Wakes”, ECN-E-09-016, Energy Research Centre of the Netherlands , 2009.