Parametric Analysis of Resistance Type Vertical Axis Wind Turbines

Transcription

1 Boletín Técnico, ol.55, Issue, 7, pp Parametric Analysis of Resistance Type ertical Axis Win Turbines Baolin Li*, Zhixin Bian, Kei hen School of Mechanical an Electrical Engineering, hina University of Mining an Technology, Xuzhou 6, hina *orresponing author( Abstract The performance of win turbines is usually evaluate by proprietary parameters, but these parameters are use to analyze the ynamic performances of the blaes qualitatively. Thus, it cannot exactly express the actual working performances of win turbines. In this paper, a comparative analysis on physical meanings is mae between resistance type vertical axis win turbines an horizontal axis win turbines. An the actual meanings of the parameters to be expresse was also iscusse. The result shows that analysis theory of blaes in ifferent type of win turbines are ifferent. An then a esign metho was put forwar to calculate an analyze the resistance type vertical axis win turbines. It is conclue that win turbines with ifferent structures an blaes have its own analysis theory an metho. Key wors: Resistance Type Win Turbine, ertical Axis Win Turbine, Dynamic Performances, omparative Analysis. INTRODUTION With the global consumption of fossil energy an the greenhouse effect cause by excessive emission of carbon ioxie, human beings are facing the ilemma of resource exhaustion an environmental eterioration. Win energy known as a clean an renewable energy, is gaining more an more attention now (Gao, ai, Pan, Guo an Shu, 7). Meanwhile, great progress has been mae in the research on win turbines, which can be ivie into horizontal axis win turbines an vertical axis win turbines. The rotating center axis of the vertical axis win turbine is perpenicular to the horizontal irection, an the structure is relatively simple to the horizontal axis win turbine. Accoring to the ifferent working principles, vertical axis win turbines can be ivie into two types of resistance type an lift type. The principle of the resistance type vertical axis win turbine is to utilize the pressure ifference which is prouce by the airflow in front an back of the blaes. Then the torque is generate by the pressure ifference to rive the blaes an the power generation equipment. An we all take Savonius win turbine as a typical example. Lift type win turbines work mainly rely on the lift of the blaes create by the airflow, an Darrieus is a typical type of win turbine(hen, Zhang, Xu an Liu, 7;Gao, Li, Ye an Nie, ;Zamani, Nazari, Moshizi an Maghrebi, 6). ertical axis win turbines possess the following avantages: () No yaw to air system that simplify the mechanical structure an control system; () The spee regulation, heat issipation an control system of the win turbines are place on the groun, so it is easy to maintain, etect an control; () Simple structure of the blaes, low level of manufacturing technology an low cost; (4) The blaes are installe to bear gravity an bening moment in the vertical irection, so low requirements are neee in structure on the strength an stiffness, an the blaes have a long working life uner the conitions (Jin, Hu an Feng, 5). Due to the above avantages, resistance type vertical axis win turbines, can be believe to have broa evelopment space an market application prospect in the future. Simultaneously, taking into account the incomplete theoretical research an eficient relate esign concepts on resistance type vertical axis win turbines, which makes it ifficult to improve the utilization coefficient of win energy. To some extent, this is the most primary reason why the evelopment of the resistance type vertical axis win turbine is limite since it has been pai attention to. Accoringly, it is necessary to carry on further stuy an analyze the parameter characteristics of the resistance type vertical axis win turbine (hen, Zhang, Xu an Liu, 7).. STRUTURAL FEATURES AND THEORY OF RESISTANE TYPE ERTIAL AXIS WIND TURBINE The utilization coefficient of win energy of the resistance type vertical axis win turbine is lower than that of the lift type win turbine, but its blaes structures are simpler an the cost is lower when compare to the lift type win turbine, so it has attracte extensive attention recently. 45

2 Boletín Técnico, ol.55, Issue, 7, pp Structure omparison Between Resistance Type an Lift Type ertical Axis Win Turbine ertical axis win turbines vary greatly in structure an blaes shape, so analysis theory is ifferent when it comes to ifferent structures. As shown in Figure, there are several common structures of the resistance type an lift type vertical axis win turbine. (a)s-type (b)open S-type (c)multiblae S-type ()Semi shiele flat type (e)φ- type (f)h-type Resistance type: (a),(b),(c),() Lift type: (e),(f) Figure. Structural iagram of vertical axis win turbine It can be seen from figure that the shape of the resistance type blaes are basically mae up of arc, semicircle or flat plate with simple section structures. These moels are easy to manufacture an realize largescale prouction an application. However, the lift type blaes are compose of irregular cambere surfaces with complex cross section structure. an the blaes will occupy a larger proportion of the cost while manufacturing high-precision surfaces(hen,zhang,xu an Liu,7;Jin,Hu an Feng,5)... Basic Theory of Resistance ertical Axis Win Turbine At present, Betz theory an blae element theory are the most popular theories in win turbines. The blae element theory is mainly use in horizontal axis win turbines(burlano,ricci,frea an Repetto,5; howhury,akimoto an Hara,6). In this paper, the main research is resistance type vertical axis win turbines, so we analyze its moel mainly by Betz theory an other relevant theories. Air flow moel base on the theory of air flow characteristics which is escribe by Bates theory is shown in Figure : Figure. Stream tube moel Hypothetical conitions of stream tube moel: () Flowing moel is forme by win wheel that can be simplifie into a stream tube, an the air in tube cannot be compresse. () The win wheel can be simplifie into a flat isk without tapere angle, eflecte angle an incline 454

3 Boletín Técnico, ol.55, Issue, 7, pp angle. () No friction is applie to the win wheel when it works. An the static airflow pressure in front of blae is equal to that in the rear of the blae. (4) Force on the blae must be uniformly. Due to the resistance of the blaes, when the air flows through the win turbine blaes, the spee ecrease obviously, however, the air pressure in the front an rear of the blae remains the same. Then, this will result in a relative small area of the tube in front of the blae an an expansion of the ownstream tube, an cross section area is much larger than the upstream. Accoring to the mass of the air remains constant uring the air flows through the blae. Then, In formula: air ensity( kg/m ); A v A v A v w w () A area of the cross section( m ); v air velocity at upstream( m/s ); A cross-sectional area at isk( m ); v air velocity at isk( m/s ); A w area of the cross section( m ); v w air velocity at ownstream( m/s ); But in fact, the hypothesis of Betz theory have a certain eviation from the actual situation: Hypothesis that the ensity of air is constant an no change in the external environment cannot be establishe. Moreover, hypothesis that the blae has the same static pressure in the front an rear is not in accorance with the actual situation. The two assumptions are base on the purpose of analyzing an calculating. In fact, ue to the compressibility of the air, space of the air ecrease when the air is flowing, an the ensity an static pressure of the air also change after air flowe through obstacles. omparatively speaking, assumptions () an (4) can be realize uner certain working conitions.. EALUATION PARAMETERS OF RESISTANE TYPE ERTIAL AXIS WIND TURBINE.. oefficient of Resistance The coefficient of resistance can be expresse as: D evice resistance( N ); air ensity( kg/m ); D A A front face area( m ); win spee( m/s ); It can be seen from the formula that the coefficient of resistance is epens on the shape of blae, win irection, win spee an air ensity... oefficient of Moment The coefficient of moment Q is use as an inex to evaluate the performance of win utilization, it also be interprete as how many moment the win turbine acquire from win, be expresse as: Q Q QU r turning raius of blae( m ); Q evice moment( Nm ); ompare to the expression of resistance coefficient, the moment coefficient is one more expression form of resistance coefficient. r () () 455

4 Boletín Técnico, ol.55, Issue, 7, pp Utilization oefficient of Win Energy Only part of the win energy can be use by win turbines an translate into mechanical energy uring the working process of the win turbines. So the utilization coefficient of win energy is eeme to evaluate the ability of absorbing an utilizing win energy from nature. The utilization coefficient of win energy P, also know as power coefficient, refers to the ratio of the actual power generate by the win turbines to the win energy of unperturbe air in the sweep range(gao,ai,pan,guo an Shu,7;Gao, Li, Ye an Nie,). Owing to partial of the win energy can be absorbe by win turbines an translate into mechanical energy.therefore, utilization coefficient of win energy is the most important parameter to evaluate aeroynamics performance of win turbines,that can be efine as: P P P the actual power generate by the win turbine ( W ); S the swept area ( m ); the velocity of the blae ege( m/s ); Taking the resistance type win turbine with flexible blaes for example,as shown in Figure, the actual power obtaine from win P is: S (4) Figure. Analysis moel of the resistance blae oefficient of blae resistance ; H blae height( m ); w angular velocity of blae( ra/s ); Make an integral of the above formula: p H( ) r H( r) rr H( r r r P H ( w r H ( w r 4 4 w r w r Make a erivation of w an get the extreme value of power P : r) r wr ) r wr ) (5) (6) 456

5 Boletín Técnico, ol.55, Issue, 7, pp p 4 4 H ( r r w r w Then, r r w r w r 58 r ) Therefore, when the ege spee of the blae is.58 times as large as the win spee, the win turbine can get the maximum power: P.58 Hr (7) Utilization coefficient of win energy is an ieal inex of the ability of power acquisition that can evaluate the performance of the win turbine. It can not juge the avantages an isavantages an the running cost of the win turbine. Therefore, the win energy utilization coefficient P is only one of the evaluation parameters an play a guiance role uring the research process. 4. OMPARISON OF DESIGN PARAMETERS BETWEEN RESISTANE TYPE ERTIAL AXIS WIND TURBINE AND HORIZONTAL AXIS WIND TURBINE 4.. Sweep Area of Blae The axis of the horizontal axis win turbine is parallel to the groun,an its swept area of blae is perpenicular to the groun.an the blae sweep area of resistance type vertical axis win turbine is a horizontal circle that the sweep raius is gyration raius an centere on rotary center.due to ifferent structures, an sweep area is also ifferent. So the sweep area of blae can not evaluate the power characteristics of win turbine accurately. The sweep form of blae on resistance type vertical axis resistance win turbine is a cyliner: S r H (8) H blae height of win turbine( m ); r turning raius of blae( m ); 4.. Aspect Ratio Aspect ratio refers to the ratio of height to gyration iameter.aspect ratio on horizontal axis win turbines show the relationship between blaes height an ability of power absorption,an it also reflect efficiency an performance of win turbines.as for resistance type vertical axis win turbine,aspect ratio has ifferent meanings,its value only represents the ratio of the height to the with of the blae(loganathan,gokhale, Kritpranam, Jitthanongsak, Date an Alam,7). So aspect ratio has no connection with performances of vertical axis win turbine. 4.. Tip Spee Ratio In orer to inicate the state of the win turbine uner ifferent win spees, the tip spee ratio is use to show the relationships between the velocity at the blae ege an win spee.an its expression is as follow: R R n (9) w angular velocity of blae( ra/s ); r turning raius of blae( m ); win spee( m/s ); n spee of the win turbine( r/min ); ertical axis win turbines are ifferent from horizontal axis win turbines in structure, an horizontal axis win turbines have a larger range of tip spee ratio than vertical axis win turbines,which is the result of the high spee about several hunre kilometers per hour at the top of horizontal axis win turbines blaes. The maximum spee of the vertical axis win turbine is the velocity of the blae ege, an value of velocity is no greater than win spee. However,the tip spee ratio will be an uncertain coefficient for the vertical axis win turbine with the guiing win structure. 457

6 Boletín Técnico, ol.55, Issue, 7, pp Soliity Soliity is the ratio of the all surfaces area of blae to the swept area, For Horizontal axis win turbines: For ertical axis win turbines: na () r ncr () r n blae number; A front face area(m ); chor length of blae(m); r turning raius of blae(m); Soliity can not accurately express the efficiency or the merits of win turbines, an ifferent win turbines with ifferent structures have no comparability an this parameter oes not has practical significance either. 5. ONLUSIONS () Due to the ifference in structures of the vertical axis win turbine an the horizontal axis win turbine,the meaning of parameters an physical expressions are totally ifferent. Therefore, the evaluation parameters an the theory of the win turbines are not universal; () The evaluation an esign parameters can't quantitatively evaluate the merits of the win turbine, On the contrary, parameters are only suitable for evaluating of the win turbine qualitatively. () Resistance coefficient of the win turbine is the most effective inicator to evaluate the performances of win turbines. But it can be influence by ifferent win spees an shapes of the obstacles. As a result, nee to be etermine by further simulation or test. REFERENES Burlano, M., Ricci, A.,Frea,A.,an Repetto, M.P.(5) Numerical an Experimental Methos to Investigate the Behavior of ertical-axis Win Turbines with Stators, Journal of Win Engineering an Inustrial Aeroynamics, 44, pp.5-. hen,j., Zhang, Z.Z., Xu, H.T., an Liu, P.W.(7) Research Status of Drag-type ertical Axis Win Turbine, Energy Engineering, 7(), pp.9-6. howhury,a.m., Akimoto, H., an Hara, Y.(6) omparative FD Analysis of ertical Axis Win Turbine in Upright an Tilte onfiguration, Renewable Energy, 85, pp.7-7. Ferrari,G., Feerici,D., Schito,P., Inzoli,F., an Mereu,R.(7) FD stuy of Savonius win turbine: D moel valiation an parametric analysis, Renewable Energy,5, pp Gao,Q., ai,x., Pan,P., Guo,X.W., an Shu,.(7) Aeroynamic haracteristics of Blae Stall Delay ontrol ertical Axis Win Turbine, Journal of entral South University, 48(), pp Gao,W., Li,., Ye,Z., an Nie,J.B.() Dynamic haracteristics an Aeroynamic Performance of ertical Win Turbine, Journal of Drainage an Irrigation Machinery Engineering, (), pp Jin,H., Hu,Y.H., an Feng,S.Q.(5) urrent Situation an Prospect on ertical Axis Win Turbine in Win Power Generation, Environmental Engineering,, pp.-8. Loganathan, B., Gokhale, P., Kritpranam, T., Jitthanongsak,P., Date, A., an Alam, F.(7) Investigate the Feasibility of High Aspect Ratio ertical Axis Win Turbine, Energy Proceia,,pp.4-9. Müller, G., havushoglu, M.,Kerri,M., an Tsuzaki,T.(7) A Resistance Type ertical Axis Win Turbine for Builing Integration, Renewable Energy,, pp Zamani,M.,Nazari,S.,Moshizi,S.A.,an Maghrebi,M.J.(6) Three Dimensional Simulation of J-shape Darrieus ertical Axis Win Turbine, Energy, 6, pp