EFFECTS OF DESIGN PARAMETERS ON WIND SPEED FOR LARGE THREE-BLADED UPWIND HORIZONTAL AXIS WIND TURBINE

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1 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: EFFETS OF DESIGN PRMETERS ON WIND SPEED FOR LRGE THREE-LDED UPWIND HORIZONTL XIS WIND TURINE 1 ZHIGNG KONG, 1 JIN WNG, YIGNG KONG 1 Scool of utomation, eijing University of Post and Telecommunications, eijing, 16, ina Scool of Mecanical Engineering, Taiyuan University of Science & Tecnology, Taiyuan 34, ina STRT For large tree-bladed upwind orizontal axis wind turbine, te blade spatial positions are different wit te rotor running at te same time, and so, te wind speed on te blade is variable due to wind sear and tower sadow. Some specific design parameters suc as rotor ub eigt, ub-eigt wind speed, wind sear coefficient, radius of te rotor disk, tower radius and overang distance are taken into account in te wind speed model. ased on te model, te influence of wind sear and tower sadow on wind speed for a twomegawatt wind turbine is investigated. Te experimental results sow tat due to te presence of wind sear and tower sadow, not only te above parameters can make te value of wind speed cange remarkably, but also tis influence is more and more serious as wind turbine capacity increases. Keywords: Design Parameters, Tower Sadow, Wind Sear, Wind Speed, Wind Turbine. 1. INTRODUTION Te wind is caracterized by its speed and direction, wic are affected by several factors, including geograpic location, climate caracteristics, eigt above ground, and surface topograpy[1]. In general, model researc and aerodynamics calculation of wind turbines ave been used were wind speed is represented eiter by ub-eigt wind speed or mean spatial wind speed[]. However, te value of wind speed in te wole rotor disk plane is unequal due to wind sear and tower sadow. For tree-bladed upwind orizontal axis wind turbine, te spatial position difference of tree blades in pairwise comparison is deg in te wole rotor disk plane. In addition, te spatial position difference between te two points on every blade is also bigger along te blade spanwise direction even if at te same azimutally angle. s nowadays wind turbine capacity is becoming bigger and bigger, te blade is longer and longer and te tower is iger and iger, te influence of wind sear and tower sadow on wind speed becomes more pronounced for te rotating blade[3]. Tis effect intensifies te periodic variation of aerodynamic load. Te periodic aerodynamic load can give rise to blade dynamic response, wic feedbacks to outside aerodynamic load, and eventually leads to torque and power generated by a wind turbine being muc more variable tan tat produced by conventional generators[4]. One of te disadvantages is tat tis makes te output unsuitable to be directly connected to te system bus because of poor power quality. Weak power systems are more susceptible to sudden canges in network operating conditions. ny major cange in te operating condition can create significant voltage and frequency fluctuation, wic can in turn make te system unstable[5,6]. Te oter problem is tat wen an unbalance load occurs among tree blades, tis brings te rotor to vibrate and fatigue []. Individual pitc control (IP) is an effective means to solve te above problems[], wic premise is te accurate calculation and analysis about te effects of design parameters on wind speed. In tis study, te wind speed model in te wole rotor disk area is obtained based on wind sear and tower sadow for tree-bladed upwind orizontal axis wind turbine. Te design parameters, suc as rotor ub eigt, ub-eigt wind speed, wind sear coefficient, radius of te rotor disk, tower radius and overang distance[], are taken into account, and te effects of tese parameters on wind speed are studied wit more details. 1

2 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: WIND SPEED MODELING y x v ( y, x) V a (4) t ( x y ) Wind speed generally increases wit eigt, wic were V is te mean spatial wind speed, a is te is known as wind sear, as sown in Figure 1. tower radius, y is te lateral distance from te Wind sear can be expressed as [1,]: blade to te tower midline, x is te distance from rcos V( r, ) V ( ) V [1 W( r, )] (1) were V is te ub-eigt wind speed, is te rotor ub eigt, r is te radial distance from te blade to te ub center, namely te blade radial distance, is te azimutal angle, and is te wind sear coefficient. wind sear coefficient is not constant and depends on numerous factors, including atmosperic conditions, temperature, pressure, umidity, time of day, seasons of te year, te mean wind speed, direction and nature of terrain. W( r, ) is te disturbance seen in wind speed due to wind sear tat is added to ub-eigt wind speed. Linearizing W( r, ) wit a tird-ordertruncated Taylor series expansion yields[]: Figure 1. Structure Of Tree-laded Upwind Horizontal xis Wind Turbine Te distribution of wind is altered by te presence of te tower. For upwind rotors, te wind directly in front of te tower is redirected and tereby reduces te torque at eac blade wen in front of te tower. Tis effect is called tower sadow. Te majority of modern wind turbines ave upwind rotors. Tis study terefore only deals wit te tower sadow wind speed in tree-bladed upwind orizontal axis rotors. Te wind speed only considering tower sadow, is given by [1,]: V( y, x) V v ( y, x) (3) t te blade origin to te tower midline, namely te overang distance, and v ( y, x ) is te disturbance t imposed by te tower sadow on wind speed. ecause te influence of tower sadow is to reduce wind speed, it is clear from Eq. 4 tat a sufficient condition for te existence of tower sadow is y x (5) Different references of wind speed are used in models for te disturbance due to wind sear and tower sadow. Te wind sear model uses ubeigt wind speed ( V ) wile te tower sadow model uses mean spatial wind speed ( V ). Te relationsip between bot wind speeds is defined as follows []: ( 1)( R ) 3 r ( 1) r ( 1)( ) r 3 W( r, ) cos cos V V [1 ] mv (6) cos 6 were R is te radius of te rotor disk, and () ( 1)( R ) m 1. onsidering Eq. 4 results in were y rsin and substituting Eq. 6 into r sin x v ( r,, x) mv a V v ( r,, x) t tt ( r sin x ) r sin x v ( r,, x) ma tt ( r sin x ) (). It sould be noted tat te tower sadow is only valid for te lower alf rotor disk plane, namely ccording to different range of te radial distance from rotor axis and te azimutal angle, te wind speed is fallen into four zones in Figure 1. Zone I: te blade works in te upper alf rotor disk plane and wind speed is only affected by wind sear. Zone II, III, IV: te blade works in te lower alf rotor disk plane. In zone II and III, wind sear and tower sadow ave influence on wind speed, but teir calculated boundaries are different and tey must be calculated respectively. In zone IV, only wind sear as influence on wind speed, but its calculated boundary is different wit Zone I, and te wind speed must be calculated respectively. For te tower in Figure 1 d a tan () were a is te top radius, d is te bottom radius, is te rotor ub eigt. onsidering d a for modern large wind turbines, te top angle of tower can be given approximately:

3 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: arc tan( ) da () Terefore, during calculating te effect of tower sadow on wind speed, it can be tink tat te radius elsewere equals te top radius approximately. In zone II, according to te Eq. 5, te blade radial distance can be deduced as follows x x r.5 1 cos( ) sin x x r cos( ) sin (1) were, 1 are te boundary azimutal angle during r R for zone II in Figure 1, tey are derived as x sin1.51 R x sin 1.5 R Eq. 1 can be represented as () x r.5, 1.5 () 1 sin In zone III, te wole blade is affected by tower sadow, te radial distance from te blade to te ub center can be written as r R () 1 Te calculated model of wind speed for four zones can be given by Zone I: Zone II: rcos V( r, ) V ( ) V[1 W( r, )] rr.5,1.5 () V(, r ) V[1 W(, r )][1 v (, r, x)] V[1 W(, r ) v (, r, x) W(, r ) v (, r, x)] tt tt tt V(, r ) V[1 W(, r )][1 v (, r, x)] V[1 W(, r ) v (, r, x) W(, r ) v (, r, x)] tt tt tt (15) s W( r, ) v ( r,, x)] would be small compared to tt oter terms, Eq. 16 is a valid approximation of Eq. 15. V( r, ) V [1 W( r, ) v ( r,, x)] (16) Zone III: Zone IV: V( r, ) V[1 W( r, ) vtt( r,, x)] x r sin.5 1, 1.5 V( r, ) V[1 W( r, ) vtt( r,, x)] rr tt (1) (1) rcos V( r, ) V( ) V[1 W( r, )] x rr sin.5 1, EXPERIMENTL RESULTS ND DISUSSION (1) onsidering te effect of wind sear and tower sadow on wind speed, te wind speed wit te cange of te blade radial distance and te azimutal angle is calculated and analysed for two megawatt tree-bladed upwind orizontal axis wind turbines. ecause cone angle and tilt angle are generally very small, tis study take tem as deg, wic means tat te blade rotates in te rotor disk plane perpendicular to te main saft axis. Te following basic values are: 6 m, V m/s,., R 3 m, a 1.5 m and x. m for design parameters. In order to fully explain te design parameters influence on wind speed wen wind sear and tower sadow are considered, tow values of tem are selected to calculate and analyse based on te basic values respectively, as sown in Table 1. Wat calls for special attention is tat it is guaranteed tat te overang distance ( x ) is greater tan te top radius ( a ) in any case. Tis is te only way to ensure te wind turbine can work normally, and experimental results can be acieved in te following figures. In zone I, i.e..5 and 1.5, te blade works in te upper alf rotor disk plane and wind speed is only affected by wind sear. Wind speed increases wit te blade radial distance ( r ) under te condition of te same azimutal angle ( ). Te maximum value of wind speed appears wen te azimutal angle is or and te blade radial distance is te radius of te rotor disk ( R ), namely at te peak of rotor disk plane (point ) in Figure 1. Table I: Te Experimental Value Of Te Design Parameters Design parameter Value 1 Value (basic) Value 3 (m) 5 6 V (m/s) R (m) a (m) x (m)

4 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: In zone.5 1.5, te blade works in te lower alf rotor disk plane. In zone II, wind speed is affected by wind sear and tower sadow, and tower sadow is more serious near te center of te rotor disk plane, namely te wind speed is smaller wit te decrease of te blade radial distance ( r ) under te condition of te same azimutal angle ( ). s te blade radial distance ( r ) gets longer, entering zone IV, wind speed is only affected by wind sear, namely te longer te blade radial distance ( r ), te smaller te wind speed. In zone III, bot wind sear and tower sadow ave effects on wind speed. Te minimum value of wind speed appears wen te azimutal angle is and te blade radial distance is te radius of te rotor disk ( R ), namely at te lowest point of rotor disk plane (point ) in Figure 1. onsidering te rotor disk plane is bilaterally symmetrical, wind speed of te rigt alf rotor disk plane is studied by te simulation experiment in tis study, i.e.. Te value of te rotor ub eigt ( ) is cosen to compare and analyse at 5, 6, and m, respectively. Figure illustrates tat as te rotor ub eigt becomes bigger, te maximum value of wind speed tends to get smaller and te minimum value of wind speed bigger. In oter words, te range of wind speed gets narrower wit te increase of rotor ub eigt Figure. Wind speed for different ( V m/s,., R 3 m, a 1.5 m, x. m): () 5 m. () 6 m. () m. Te ub-eigt wind speed ( V ) is cosen to compare and analyse at,, and m/s. It is obvious tat te mean wind speed, te maximum and minimum wind speed rise wit te increase of te ub-eigt wind speed in Figure 3.

5 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: Figure 3. Wind speed for different V ( 6 m,., R 3 m, a 1.5 m, x. m): () V m/s. () V m/s. () V m/s. Te wind sear coefficient ( ) is cosen to compare and analyse at.15,., and.5, respectively. Figure 4 sows tat te vertical cange of wind speed is related to te wind sear coefficient and its value embodies te canging ratio of wind speed wit vertical eigt. Te bigger te value of wind sear coefficient, te faster te cange of te wind speed wit vertical eigt, namely te wind speed gradient is big; te smaller te value of wind sear coefficient, te slower te cange of te wind speed wit vertical eigt, namely te wind speed gradient is small Figure 4. Wind speed for different ( 6 m, V m/s, R 3 m, a 1.5 m, x. m): ().15. ().. ().5. 3

6 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: Te radius of te rotor disk ( R ) is cosen to compare and analyse at 33, 3, and 43 m, respectively. Figure 5 indicates tat similar to te cange of wind sear coefficient, te bigger te value of te blade radius, te larger te difference between te maximum and te minimum value of wind speed, namely te range of wind speed tends to be wider wit te increase of te radius of te rotor disk W in d s p e e d (m /s ) W ind speed (m /s) Figure 5. Wind speed for different R ( 6 m, V m/s,., a 1.5 m, x. m): () R 33 m. () R 3 m. () R 43 m. Te top radius ( a ) is cosen to compare and analyse at 1.1, 1.5, and 1. m. Te influence of te cange of te top radius on wind speed in te upper alf rotor disk plane is small enoug to be negligible, but te wind speed in te lower alf rotor disk plane decreases wit te increase of te top radius. Te reason is tat wind sear is basically irrelevant to te top radius, but tower sadow is positively correlated to te top radius. Tis may be correlated to te trend exibited in Figure Figure 6. Wind speed for different a ( 6 m, V m/s,., R 3 m, x. m): () a 1.1 m. () a 1.5 m. () a 1. m. Te overang distance ( x ) is cosen to compare and analyse at.4,., and 3.4 m, respectively. It is clear from Figure tat te influence of te cange of te overang distance on wind speed in te upper 4

7 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: alf rotor disk plane is small enoug to be 4. ONLUSION negligible, but te wind speed in te lower alf rotor disk plane decreases wit te decrease of te overang distance. In oter words, te closer te rotor disk plane from te tower, te more evident te effect of tower sadow Due to te presence of wind sear and tower sadow, wind speed is not fixed in te wole rotor disk plane, and moreover it is closely related to rotor ub eigt, ub-eigt wind speed, wind sear coefficient, radius of te rotor disk, tower radius and overang distance. s nowadays wind turbine capacity is becoming bigger and bigger, te blade is longer and longer and te tower is iger and iger, and te influence of wind sear and tower sadow on wind turbine is more serious. It is obvious tat simplifying or neglecting wind sear and tower sadow is not precise and reasonable in design and calculation for wind turbine. ased on te in-dept researc of wind sear and tower sadow, tis study implements te dynamic response model of wind speed wit te cange of te blade radial distance and te azimutal angle, and analyse te effects of design parameters on wind speed for large orizontal axis wind turbine. Tis work lays a foundation for furter study of te individual pitc, power control, fatigue, dynamic stability and etc. for wind turbine Figure. Wind speed for different x ( 6 m, V m/s,., R 3 m, a 1.5 m): () x.4 m. () x. m. () x 3.4 m. KNOWLEDGMENTS Te autors gratefully acknowledge te inese Universities Scientific Fund (R63) and Taiyuan University of Science & Tecnology Doctoral Fund ( ). REFERENES [1] J. E. Payne,. arroll, Modeling wind speed and time-varying turbulence in geograpically dispersed wind energy markets in ina, Energy Sources Recovery Util. Environ. Eff., Vol. 31, No. 1,, pp []. L. ottasso,. roce, Y. Nam, Power curve tracking in te presence of a tip speed constraint, Renew. Energy, Vol. 4, No.1,, pp. 1-. [3] S. Reman, M.. Naif, Wind sear coefficients and teir effect on energy production, Energy onvers Manage, Vol. 46, No. 15, 5, pp [4] H. Geng, G. Yang, Output power control for variable-speed variable-pitc wind generation systems, IEEE Trans Energy onvers, Vol. 5, No., 1, pp

8 Journal of Teoretical and pplied Information Tecnology 15 t November. Vol. 45 No JTIT & LLS. ll rigts reserved. ISSN: E-ISSN: [5] F. M. Huges, R. naya-lara, G. Olimpo, J.Nicolas, G. Strbac, Influence of tower sadow and wind turbulence on te performance of power system stabilizers for DFIG-based wind farms, IEEE Trans Energy onvers, Vol. 3, No.,, pp [6] L. Li, N.. Zou, J. Z. Zu, nalysis of voltage stability in a practical power system wit wind power, Electr. Power omp. Syst, Vol. 3, No., 1, pp []. J. Eggers, R. Digumarti, K. aney, Wind sear and turbulence effects on rotor fatigue and loads ontrol, J Sol Energy Eng Trans SME, Vol. 5, No. 4, 3, pp.4-4. [] T. J. Larsen,. Helge, ctive load reduction using individual pitc, based on local blade flow measurements, Wind Energy, Vol., No. 1, 5, pp. 6- [] E.. ossanyi, laded for Windows User Manual. ristol, U.K., 5. Garrad Hassan and Partners Limited. [1] T. ckerman, Wind Power in Power System, New York, 5. Jon Wiley & Sons. [] D.. Spera. Wind Turbine Tecnology. New York, 14. SME Press. [] D. S. L. Dolan, P. W. Len, Simulation model of wind turbine 3p torque oscillations due to wind sear and tower sadow, IEEE Trans Energy onvers, Vol. 1, No. 3, 6, pp