- Email: [email protected]
Review of savonius wind turbine design and performance
Available online at www.sciencedirect.com Available online at www.sciencedirect.com
ScienceDirect ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
Energy Procedia 00 (2017) 000–000 ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2017) 000–000 383–388 EnergyProcedia Procedia141 00 (2017) www.elsevier.com/locate/procedia
4th International Conference on Power and Energy Systems Engineering, CPESE 2017, 25-29 2017, Berlin, Germany 4th International Conference September on Power and Energy Systems Engineering, CPESE 2017, 25-29 September 2017, Berlin, Germany
Review savonius wind turbine designHeating and performance Theof15th International Symposium on District and Cooling Review of savonius wind turbine design and performance a, a M.ZEMAMOU *, M.AGGOUR , A.TOUMIb a, b *,of M.AGGOUR A.TOUMI Assessing M.ZEMAMOU the feasibility using thea, heat demand-outdoor LR2E,University Ibn Tofail, Avenue de L'Université, Kénitra, Morocco laboratory of international university Rocade 11100 Sala Al Jadida, Rabat, Morocco LR2E,University Avenue deShore L'Université, Kénitra, Morocco temperature function forofIbnrabat,Technopolis aTofail, long-term district heat demand forecast a
b
a
laboratory of international university of rabat,Technopolis Shore Rocade 11100 Sala Al Jadida, Rabat, Morocco
b
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b
Recherche & Innovation, 291 Avenue Daniel, 78520 The world adopts a policy Veolia of energy transition, which refers toDreyfous the substitution of Limay, fossil France fuels by renewable energies c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, Nantes, France to reduce however the transition, major issuewhich is to develop wind turbine which has fuels a44300 simple design, a relatively 2 emission, The worldCO adopts a policy of energy refers toathe substitution of fossil by renewable energies lowreduce operating and however independent wind directions, savonius rotor appears to behas promising such aconditions, to CO2 speed emission, the major issue is to the develop a wind turbine which a simplefor design, relatively but suffers from major low efficiency and the high negativerotor torque.so scientific aims low operating speed anddrawbacks: independent wind directions, savonius appearsfartoseveral be promising for researchers such conditions, toAbstract improve the performances of savonius turbine, by the effects of different geometric and by but suffers from major drawbacks: low efficiency andoptimizing high negative torque.so far several scientificparameters researchers aims developing newperformances design. The range of the power coefficient valuesthe foreffects the conventional rotors is between to improve the of savonius turbine, by optimizing of differentSavonius geometric parameters and0.1 by and 0.25 .The installation of several set leads to new values designs which achieve an improvement infor the coefficientthe developing new design. of extra theaddressed power coefficient theofconventional Savonius rotors is between District heating networksThe arerange commonly in the literature asforone the most effective solutions decreasing0.1 of performance of 27.3% compared to the conventional rotor. and 0.25 .The installation of several extra set leads to new designs which achieve an improvement in the coefficient greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat © 2017 The Authors. Published by Elsevier Ltd. of performance of 27.3% compared to the conventional rotor. DueAuthors. to the changed conditions ©sales. 2017 The Publishedclimate by Elsevier Ltd. and building renovation policies, heat demand in the future could decrease,
Peer-review responsibility of Elsevier the organizing committee of CPESE 2017. © 2017 The under Authors. Published by Ltd. committee prolonging the investment return Peer-review under responsibility ofperiod. the scientific of the 4th International Conference on Power and Energy Peer-review under responsibility of the organizing committee of CPESE Systems Engineering. The main scope of this paper is to assess the feasibility of using the heat2017. demand – outdoor temperature function for heat demand Keywords:Power coefficient; Savonius rotor; torque coefficient;Wind turbine.
forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665
Keywords:Power Savonius rotor; torque coefficient;Wind turbine. buildings that coefficient; vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district
scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were 1.renovation Introduction compared with results from a dynamic heat demand model, previously developed and validated by the authors. 1.The Introduction results showed that when only weather change is considered, the margin of error could be acceptable for some applications Wind turbines fall into two main categories: HAWT horizontal axis wind turbines and VAWT vertical axis wind (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation turbines. HAWT are the they(depending are generally more efficient than VAWT leastcombination forvertical laminarconsidered). winds of Wind turbines fall intomost twowidespread main HAWT horizontal axis and wind turbines andat VAWT axis wind scenarios, the error value increased upcategories: to 59.5% on the weather renovation scenarios high speeds. However, they operate poorly in unstable winds or uncertain directions. On the other hand Savonius wind turbines. HAWT are the most widespread they are generally more efficient than VAWT at least for laminar winds of The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the turbine which is number classified among thepoorly VAWT have during a simple operate independently ofhand the direction of the high speeds. However, they operate in unstable winds or uncertain directions. On Savonius wind decrease in the of heating hours of 22-139h theconstruction heating season (depending onthe theother combination of weather and wind and starts lowconsidered). windamong speedOn itthe was developed patented by S.J. Savonius in the 1920s according to savonius renovation scenarios the other hand, intercept increased for 7.8-12.7% per decade the turbine which isatclassified VAWT have and afunction simple construction operate independently of the (depending direction ofonthe coupled The values suggested could beofused modify the function parameters for1920s theprototype scenarios considered, and the best his rotors had a maximum efficiency 31% while theby maximum efficiency the was [1]. wind andofscenarios). starts at low wind speed it was developed and to patented S.J. Savonius in theof according to 37% savonius improve of heat demand estimations. the best ofthe hisaccuracy rotors had a maximum efficiency of 31% while the maximum efficiency of the prototype was 37% [1]. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +6-064-477-23. Cooling.
E-mail address:author. [email protected] * Corresponding Tel.: +6-064-477-23. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review the organizing committee 1876-6102 ©under 2017responsibility The Authors. of Published by Elsevier Ltd. of CPESE 2017. Peer-review under responsibility of the organizing committee of CPESE 2017.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 4th International Conference on Power and Energy Systems Engineering. 10.1016/j.egypro.2017.11.047
M. Zemamou et al. / Energy Procedia 141 (2017) 383–388 M.ZEMAMOU et al. / Energy Procedia00 (2017) 000–000
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Despite its various qualities savonius turbine suffer from a major drawback of low efficiency, over the years, extensive studies experimental, theoretical or numerical have been reported to identify a new design and they have proved a deep improvement at the level of power coefficient compared to conventional Savonius rotors [2],which have range values of power coefficient between 0.1 and 0.25[3]. Nomenclature ρ S V PT PA Cp ω E
density of air ( = 1.225 kg/m3) swept area of blades (m²) wind speed (m/s) . maximum power obtained from the wind (watt) total power available from the wind (watt) coefficient of power angular velocity of rotor (1/s) overlap ratio e/D
T Tw H AR Cm R λ D θ
actual torque develop by the rotor (N.m) theoretical torque available in the wind (N.m) rotor height (m) aspect ratio H/D torque coefficient radius of rotor (m) tip speed ratio rotor diameter (m) rotor blade angle(degree)
2. Working principle: The Savonius wind turbine is a simple vertical axis device having a shape of half-cylindrical parts attached to the opposite sides of a vertical shaft (for two-bladed arrangement) and operate on the drag force, so it can’t rotate faster than the wind speed. This means that the tip speed ratio is equal to 1 or smaller [4].As the wind blows into the structure and comes into contact with the opposite faced surfaces (one convex and other concave), two different forces (drag and lift) are exerted on those two surfaces. The basic principle is based on the difference of the drag force between the convex and the concave parts of the rotor blades when they rotate around a vertical shaft. Thus, drag force is the main driving force of the savonius rotor [5]. Fig.1.(a) shows characteristic parameters of a savonius wind turbine with two semi circular profile blades. (a) (b)
Figure.1. (a) two-bladed Savonius rotor, (b) Conventional Savonius rotor performance [6]
Butaud and Besnard have highlighted the concept of drag wind turbine for Savonius turbine. The dynamic analysis of its operation shows the influence of lift force. The Savonius can’t really be classified into one or the other of these categories. Its efficiency at starting is in fact mainly due to drag force, but its maintenance in rotation is mainly due to the force of lift[7]. 3. Performance of Savonius turbine The performance of Savonius wind turbine can be expressed in the form of coefficient of power Cp Eq.(4) and torque coefficient Cm Eq.(5) in comparison with the tip speed ratio (TSR) λ Eq.(1). TSR is a ratio between the speed of tip blade and wind speed through the blade obtained by Eq.(1)[8]. Vrotor R (1) V V
M. Zemamou et al. / Energy Procedia 141 (2017) 383–388 M.ZEMAMOU et al. / Energy Procedia00 (2017) 000–000
PA Kinetic energy mass flow rate=
1 V ² SV 2
PT T(watt ) C p
PT PA
PT 1 SV 3 2
C m
T 4T TW SV ²
385
(2) (3) (4)
(5)
Conventional Savonius rotor is a rotor with the geometrical parameters a and e are respectively equal to 0 and D/6.This rotor has been largely studied [9]. The values of Cp and Cm are experimentally determined as a function of the velocity coefficient λ, Fig.1 (b). 4. Parameters that affect the performance of Savonius wind turbine 4.1. Effect of blades number The number of blades have an important impact in the rotor's performance. U.K. Saha and S. Thotla[10] conclude that the optimum number of blades is two for the Savonius rotor whether it is single, two or three stage,M.Hadi Ali [11] also conclude that the two blades Savonius wind turbine is more efficient, it has higher power coefficient under the same test condition than that of three blades Savonius wind turbine Fig.2.(a). (a) (b)
Figure.2. (a) The Cp variation with the TSR for two & three blades.[11], (b) Variation of Cp with wind speed for different aspect ratios[12]
4.2 effect of Aspect Ratio The aerodynamic performance of the Savonius rotor depends strongly on the aspect ratio (AR). N.H. Mahmoud [12] tested different configurations for aspect ratios (noted α) of 0.5, 1, 2,4,5 by keeping other parameters constant, the results show that the power coefficient increases with the rise in aspect ratio Fig.2.(b),Lately, studies with various designs of changed Savonius rotor having low ARs have been reported out. According to Kamoji [13] The rotor with an aspect ratio of 0.7 is having a maximum Cp equal to 0.21. Modi [14] also conclude that an AR of 0.77 leads to
M. Zemamou al. / Energy Procedia 141 000–000 (2017) 383–388 M.ZEMAMOU et al. /etEnergy Procedia00 (2017)
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a maximum Cp of 0.24 However, several studies on Savonius new rotors use AR near to 1 [15], generally the use of ARs within the range of 1.5–2.0 set good results on the performance of the Savonius rotor. 4.3 Effect of overlap ratio The overlap ratio is a major parameter that influences the structure of the flow inside the rotor and consequently its aerodynamic performances, the influence of the overlap ratio has been widely investigated, however there is not an accord among the outcomes acquired in previous studies. According to Blackwell [16] the optimal value of overlap ratio is in the range of 0.1 to 0.15. J.Menet [17] indicate that the primary overlap ratio must be between 0.15 and 0.3 and the optimal value equal to 0.242.Akwa [18] has also done a detailed investigation on the effect of overlap ratio and indicate that the configuration of Savonius rotor that shows the best performance is the one where the overlap ratio equal to 0.15, which gives an averaged power coefficient equal to 0.3161 for the TSR of 1.25. 5
New design
Recently scientific research have introduced new rotor designs by adding extra sets to the conventional rotor reach a to a better performance .The following part clarifies the different new design developed: 5.1 Obstacle shielding returning blade with optimized blade shape design: The installation of obstacle plate shields partly the returning blade of a savonius turbine and that optimizes the wind direction toward the advancing blade, the new design improves the self-starting capability for Savonius rotor. While the conventional savonius turbine shows a negatives values for the static moment in some range of rotation angle, the obstacle leads to a positive static moment value at any angle. The idea of introducing an obstacle in the design of the turbine was developed later in order to specify the optimal position of the obstacle to achieve better performance. The optimal position of obstacle plate is (X1/R = -1.2383, Y1/R = -0.4539, X2/R = -1.0999 and Y2/R = 1.1770, which leads to an angle β = 100.8° fig.3.(a), this optimal configuration leads to a peak power output coefficient of 0.258 at λ= 0.8[19]. In order to reach the maximum power coefficient a complementary study has been established, the obstacle plate is kept fixed in the optimal position and they investigate the optimization of the blade shape, the optimization is used to find the best blade shape while taking into account the obstacle shielding the returning blade in the optimum position. The free design variables considered for the optimization thus describe the blade skeleton line for a constant blade thickness of 2 mm. For this purpose, six parameters are considered (X P1, YP1, XP2, YP2, XP3 and YP3, Fig.3.(b), so the optimal shape is found for following values X P1/r=0.6909, YP1/r=0.0386,XP2/r=0.3940,YP2/r=-0.6067,XP3/r=0.6389,YP3/r =0.6357 fig.3.(b).This optimization procedure is able to identify considerably better configurations than the standard Savonius turbine, leading to a relative increase of the power output coefficient by 38.9% at λ= 0.7. This positive effect is also observed for the torque coefficient. The absolute performance increase is even higher for smaller values of λ, while the highest relative increase (75.4%) is observed at λ = 1.4 [20]. 5.2 blade Curtaining design To improve the performance and increase the efficiency of Savonius rotor without changing the basic structure of the Rotor, a curtain arrangement made up from wind deflecting plates has been designed and placed in front of the rotor, there are four variables on the curtain arrangement. These are lengths of the curtain blades (l 1 and l2) and the angles of the blades (α and β) fig.3.(c) the minimum value of α has been determined as 30°which can prevent the wind force on the convex blade. The angle has been increased up to 60° with 5° increments in the study, β angle has been considered in the range of (0–30°). The lengths of the curtains have been initially adjusted to cover the effective flow field. Then, l1 and l2 lengths have been increased gradually to find the optimum lengths which generate maximum torque, power and power coefficient. Experiments have been conducted by using the arrangement of Savonius wind rotor without curtain and with three different curtains at different angles (α and β). The highest power coefficient has Been obtained with the curtain 1 arrangement (l1 =45cm, l2=52 cm, α = 45° and β= 15°) with an increase38%[21].
M. Zemamou et al. / Energy Procedia 141 (2017) 383–388 M.ZEMAMOU et al. / Energy Procedia00 (2017) 000–000
(a) (a)
387
(b) (b)
(d)
(c)
(f) (g)
(e)
Fig. 3. various new design of savonius rotor: (a) ostacle shielding returning blade[19] , (b) Obstacle shielding with optimized blade shape design [20],(c) Curtain design [21]. (d) V-blade [22] , (e) quarter blade[23], (f) conveyor-deflector curtain[24] (g) combined blade[25]. Table 1: comparison of the maximum power coefficient obtained for new design of Savonius rotor Author M.H. Mohamed,D. Thévenin [19] M.H. Mohamed, D. Thévenin[20] B. D.Altan , M.Atılgan [21] H. E. Gad,A. A. Abd El-Hamid [22] S.Sharma,R. Kumar [23] M.Tartuferia,,V.D'Alessandro[24] A. Sanusi ,S.Soeparman [25] Y.X. Yao, Z.P. Tang [26] G. Kailash [27],,Ogawa [28] S.Iio , Y.Katayama[29]
new design Obstacle shielding Obstacle shield optimized blade Curtain design V-shaped blade Multiple quarter blades Conveyor-deflector curtain system Combined Blade Tower cowling Deflector plate Shield Plat
Cp max 27.3% increase from the conventional rotor 38.9% increase from the conventional rotor 38 % increase from the conventional rotor 0.37 8.89% increase from the conventional rotor 20% increase from the conventional rotor 11 % increase from the conventional rotor 0.48 0.35, 24% increase from the conventional rotor 0.47
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M. Zemamou et al. / Energy Procedia 141 (2017) 383–388 M.ZEMAMOU et al. / Energy Procedia00 (2017) 000–000
5.3 V-shape Blade The study includes seven shapes of modified blade in addition to the conventional Savonius rotor. The results showed that the Modify 4 fig.3 (d) rotor has the best values of average torque and average Cp at TSR up to 0.9 [22]. Conclusion The Savonius rotor has proven its performance due to its simple design, low cost and low starting torque at low wind speed despite its low efficiency caused by the negative torque applied to the returning blade, for years several researches aim to improve the design of Savonuis rotor in order to achieve better performance. This paper aims to compare several results of published articles on performance of new designs of Savonius rotor. It is intended to provide an important background for future studies on this type of wind turbine. According to this review result we conclude that over the years, the development of the shape of Savonius rotor blade remains a very promising research field in order to improve the performance of the rotor, It is perceived that research on parameters such as AR, overlap ratio and number of blade can be more studied to arrive at a satisfactory level of performance, although adding an extra set like obstacle shielding, curtain or conveyor deflector improve the performance of Savonius these developed designs of Savonius have made this rotor system very complex and dependent on the direction which represent a major drawback of this studies, in this context the search for a compromise between rotor efficiency and system simplicity is a promising area of research for future works. References.
[1] “Savonius SJ. The S-rotor and its applications.Mech Eng,” 1931. [2] “A.Al-Faruk, A.Sharifian, ‘Flow field and performance study of vertical axis Savonius type SST wind turbine’, Energy Procedia 110 ( 2017) 235 – 242.2017. [3] F.Jamati, étude numérique d’une éolienne hybride asynchrone. 2011. [4] M. D’Ambrosio, Vertical Axis Wind Turbines: History, Technology and Applications. 2010. [5] S. Roy and U. K.Saha, “Review of experimental investigations into the design, performance and optimization of the Savonius rotor,” 227 (4) 528-542 2013. [6] “J.Martin "Energies éoliennes, Techniques de l’Ingénieur "B1360 : 1-21, France 1997. [7] P.Butaud,A.Besnard, “Etude aérodynamique instationnaire d’un rotor d’éolien de Savonius : mise en évidence de l’influence de la portance,” 21eme Congrès Français de Mécanique,2013. [8] “K.K. Sharma, R. Gupta, A.Biswas,‘Performance Measurement of a Two-Stage Two-Bladed Savonius Rotor’Vol.4, No.1, 2014. [9] Le Gourières D, Énergie éolienne, Eyrolles, Paris,1980. [10] U.K. Saha and S. Thotla, “Optimum design configuration of Savonius rotor through wind tunnel experiments,”96 (2008)1359–1375,2008. [11] M. H.Ali, “Experimental Comparison Study for Savonius wind turbine of two & three blades at low wind speed,”pp-2978-2986 2013. [12] N.H. Mahmoud, and , A.El Haroun, “An experimental study on improvement of Savonius rotor performance,” (2012) 51, 19–25, 2012. [13] M.A. Kamojia and , S.B. Kedare, “Experimental investigations on single stage modified Savonius rotor,” 86 (2009) 1064–1073, 2008. [14] V.J.Modi,N.Roth,“optimum configuration studies and prototype design of a wind energy operated irrigation system,”16 (1984) 85-96, 1984. [15] R.Pudur and S.Gao, “Performance analysis of Savonius rotor on different aspect ratio for hydropower generation,” ICPDEN 2015. [16] Ben F. Blackwell, Robert, “Wind Tunnel Performance Data for two- and Three-Bucket Savonius Rotors,” 1977. [17] J.L.Menet, and N. Bourabaa, “increase in the savonius rotors efficiency via a parametric investigation.”2004. [18] J.V.Akwa and Gi.A.Júnior, “Discussion on the verification of the overlap ratio influence on performance coefficients of a Savonius wind rotor using computationalfluid dynamics,” 38 (2012) 141e149, 2011. [19] M.H. Mohamed, G. Janiga, E. Pap, D. Thévenin, “Optimization of Savonius turbines using an obstacle shielding the returning blade,” 35(2010) 2618-2626,2010.. [20] M.H.Mohamed, G. Janiga, E. Pap, D. Thévenin, “Optimal blade shape of a modified Savonius turbine using an obstacle shielding the returning blade,” 52 (2011) 236–242,2010. [21] B.D.Altan, and ,M.Atılgan, “An experimental study on improvement of a Savonius rotor performance with curtaining,” 1673–1678,2008. [22] H. E. Gad, and A.Abd El-Hamid, “A New Design of Savonius Wind Turbine: Numerical Study,” 6(4) 2014. [23] S.Sharma,and R. Kumar Sharma, “Performance improvement of Savonius rotor using multiple quarter blades ” (2016) 43–54,2016. [24] M.Tartuferia and V.D’Alessandro, “Enhancement of Savonius wind rotor aerodynamic performance: a computational study of new blade shapes and curtain systems,” 79 (2015) 37-384 2014. [25] A. Sanusi , S.Soeparman, “Experimental Study of Combined Blade Savonius Wind Turbine,” 6, No. 2, 2016. [26] Y.X. Yao, Z.P. Tang, “Design based on a parametric analysis of a drag driven VAWT with a tower cowling,” 116(2013)32–39, 2013. [27]G. Kailash, T. I. Eldho, “Performance Study of Modified Savonius Water Turbine with Two Deflector Plates,” Article ID 679247,2012. [28]Ogawa and Yoshida, “Effects of a deflecting plate and rotor end plates on performance of Savonius type wind turbine,” 29-253,1986. [29]S.Iio , Y.Katayama, F.Uchiyama, E.Sato and T.Ikeda,“Influence of Setting Condition on Characteristics of Savonius Hydraulic Turbine with a Shield Plate,” 20, No.3(2011) 224-228 ,2011.
ScienceDirect ScienceDirect Availableonline onlineatatwww.sciencedirect.com www.sciencedirect.com Available Energy Procedia 00 (2017) 000–000
Energy Procedia 00 (2017) 000–000 ScienceDirect ScienceDirect
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
Energy (2017) 000–000 383–388 EnergyProcedia Procedia141 00 (2017) www.elsevier.com/locate/procedia
4th International Conference on Power and Energy Systems Engineering, CPESE 2017, 25-29 2017, Berlin, Germany 4th International Conference September on Power and Energy Systems Engineering, CPESE 2017, 25-29 September 2017, Berlin, Germany
Review savonius wind turbine designHeating and performance Theof15th International Symposium on District and Cooling Review of savonius wind turbine design and performance a, a M.ZEMAMOU *, M.AGGOUR , A.TOUMIb a, b *,of M.AGGOUR A.TOUMI Assessing M.ZEMAMOU the feasibility using thea, heat demand-outdoor LR2E,University Ibn Tofail, Avenue de L'Université, Kénitra, Morocco laboratory of international university Rocade 11100 Sala Al Jadida, Rabat, Morocco LR2E,University Avenue deShore L'Université, Kénitra, Morocco temperature function forofIbnrabat,Technopolis aTofail, long-term district heat demand forecast a
b
a
laboratory of international university of rabat,Technopolis Shore Rocade 11100 Sala Al Jadida, Rabat, Morocco
b
I. Andrića,b,c*, A. Pinaa, P. Ferrãoa, J. Fournierb., B. Lacarrièrec, O. Le Correc
Abstract a IN+ Center for Innovation, Technology and Policy Research - Instituto Superior Técnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal Abstract b
Recherche & Innovation, 291 Avenue Daniel, 78520 The world adopts a policy Veolia of energy transition, which refers toDreyfous the substitution of Limay, fossil France fuels by renewable energies c Département Systèmes Énergétiques et Environnement IMT Atlantique, 4 rue Alfred Kastler, Nantes, France to reduce however the transition, major issuewhich is to develop wind turbine which has fuels a44300 simple design, a relatively 2 emission, The worldCO adopts a policy of energy refers toathe substitution of fossil by renewable energies lowreduce operating and however independent wind directions, savonius rotor appears to behas promising such aconditions, to CO2 speed emission, the major issue is to the develop a wind turbine which a simplefor design, relatively but suffers from major low efficiency and the high negativerotor torque.so scientific aims low operating speed anddrawbacks: independent wind directions, savonius appearsfartoseveral be promising for researchers such conditions, toAbstract improve the performances of savonius turbine, by the effects of different geometric and by but suffers from major drawbacks: low efficiency andoptimizing high negative torque.so far several scientificparameters researchers aims developing newperformances design. The range of the power coefficient valuesthe foreffects the conventional rotors is between to improve the of savonius turbine, by optimizing of differentSavonius geometric parameters and0.1 by and 0.25 .The installation of several set leads to new values designs which achieve an improvement infor the coefficientthe developing new design. of extra theaddressed power coefficient theofconventional Savonius rotors is between District heating networksThe arerange commonly in the literature asforone the most effective solutions decreasing0.1 of performance of 27.3% compared to the conventional rotor. and 0.25 .The installation of several extra set leads to new designs which achieve an improvement in the coefficient greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat © 2017 The Authors. Published by Elsevier Ltd. of performance of 27.3% compared to the conventional rotor. DueAuthors. to the changed conditions ©sales. 2017 The Publishedclimate by Elsevier Ltd. and building renovation policies, heat demand in the future could decrease,
Peer-review responsibility of Elsevier the organizing committee of CPESE 2017. © 2017 The under Authors. Published by Ltd. committee prolonging the investment return Peer-review under responsibility ofperiod. the scientific of the 4th International Conference on Power and Energy Peer-review under responsibility of the organizing committee of CPESE Systems Engineering. The main scope of this paper is to assess the feasibility of using the heat2017. demand – outdoor temperature function for heat demand Keywords:Power coefficient; Savonius rotor; torque coefficient;Wind turbine.
forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665
Keywords:Power Savonius rotor; torque coefficient;Wind turbine. buildings that coefficient; vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district
scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were 1.renovation Introduction compared with results from a dynamic heat demand model, previously developed and validated by the authors. 1.The Introduction results showed that when only weather change is considered, the margin of error could be acceptable for some applications Wind turbines fall into two main categories: HAWT horizontal axis wind turbines and VAWT vertical axis wind (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation turbines. HAWT are the they(depending are generally more efficient than VAWT leastcombination forvertical laminarconsidered). winds of Wind turbines fall intomost twowidespread main HAWT horizontal axis and wind turbines andat VAWT axis wind scenarios, the error value increased upcategories: to 59.5% on the weather renovation scenarios high speeds. However, they operate poorly in unstable winds or uncertain directions. On the other hand Savonius wind turbines. HAWT are the most widespread they are generally more efficient than VAWT at least for laminar winds of The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the turbine which is number classified among thepoorly VAWT have during a simple operate independently ofhand the direction of the high speeds. However, they operate in unstable winds or uncertain directions. On Savonius wind decrease in the of heating hours of 22-139h theconstruction heating season (depending onthe theother combination of weather and wind and starts lowconsidered). windamong speedOn itthe was developed patented by S.J. Savonius in the 1920s according to savonius renovation scenarios the other hand, intercept increased for 7.8-12.7% per decade the turbine which isatclassified VAWT have and afunction simple construction operate independently of the (depending direction ofonthe coupled The values suggested could beofused modify the function parameters for1920s theprototype scenarios considered, and the best his rotors had a maximum efficiency 31% while theby maximum efficiency the was [1]. wind andofscenarios). starts at low wind speed it was developed and to patented S.J. Savonius in theof according to 37% savonius improve of heat demand estimations. the best ofthe hisaccuracy rotors had a maximum efficiency of 31% while the maximum efficiency of the prototype was 37% [1]. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and * Corresponding author. Tel.: +6-064-477-23. Cooling.
E-mail address:author. [email protected] * Corresponding Tel.: +6-064-477-23. E-mail address: [email protected] Keywords: Heat demand; Forecast; Climate change 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review the organizing committee 1876-6102 ©under 2017responsibility The Authors. of Published by Elsevier Ltd. of CPESE 2017. Peer-review under responsibility of the organizing committee of CPESE 2017.
1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the Scientific Committee of The 15th International Symposium on District Heating and Cooling. 1876-6102 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 4th International Conference on Power and Energy Systems Engineering. 10.1016/j.egypro.2017.11.047
M. Zemamou et al. / Energy Procedia 141 (2017) 383–388 M.ZEMAMOU et al. / Energy Procedia00 (2017) 000–000
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Despite its various qualities savonius turbine suffer from a major drawback of low efficiency, over the years, extensive studies experimental, theoretical or numerical have been reported to identify a new design and they have proved a deep improvement at the level of power coefficient compared to conventional Savonius rotors [2],which have range values of power coefficient between 0.1 and 0.25[3]. Nomenclature ρ S V PT PA Cp ω E
density of air ( = 1.225 kg/m3) swept area of blades (m²) wind speed (m/s) . maximum power obtained from the wind (watt) total power available from the wind (watt) coefficient of power angular velocity of rotor (1/s) overlap ratio e/D
T Tw H AR Cm R λ D θ
actual torque develop by the rotor (N.m) theoretical torque available in the wind (N.m) rotor height (m) aspect ratio H/D torque coefficient radius of rotor (m) tip speed ratio rotor diameter (m) rotor blade angle(degree)
2. Working principle: The Savonius wind turbine is a simple vertical axis device having a shape of half-cylindrical parts attached to the opposite sides of a vertical shaft (for two-bladed arrangement) and operate on the drag force, so it can’t rotate faster than the wind speed. This means that the tip speed ratio is equal to 1 or smaller [4].As the wind blows into the structure and comes into contact with the opposite faced surfaces (one convex and other concave), two different forces (drag and lift) are exerted on those two surfaces. The basic principle is based on the difference of the drag force between the convex and the concave parts of the rotor blades when they rotate around a vertical shaft. Thus, drag force is the main driving force of the savonius rotor [5]. Fig.1.(a) shows characteristic parameters of a savonius wind turbine with two semi circular profile blades. (a) (b)
Figure.1. (a) two-bladed Savonius rotor, (b) Conventional Savonius rotor performance [6]
Butaud and Besnard have highlighted the concept of drag wind turbine for Savonius turbine. The dynamic analysis of its operation shows the influence of lift force. The Savonius can’t really be classified into one or the other of these categories. Its efficiency at starting is in fact mainly due to drag force, but its maintenance in rotation is mainly due to the force of lift[7]. 3. Performance of Savonius turbine The performance of Savonius wind turbine can be expressed in the form of coefficient of power Cp Eq.(4) and torque coefficient Cm Eq.(5) in comparison with the tip speed ratio (TSR) λ Eq.(1). TSR is a ratio between the speed of tip blade and wind speed through the blade obtained by Eq.(1)[8]. Vrotor R (1) V V
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PA Kinetic energy mass flow rate=
1 V ² SV 2
PT T(watt ) C p
PT PA
PT 1 SV 3 2
C m
T 4T TW SV ²
385
(2) (3) (4)
(5)
Conventional Savonius rotor is a rotor with the geometrical parameters a and e are respectively equal to 0 and D/6.This rotor has been largely studied [9]. The values of Cp and Cm are experimentally determined as a function of the velocity coefficient λ, Fig.1 (b). 4. Parameters that affect the performance of Savonius wind turbine 4.1. Effect of blades number The number of blades have an important impact in the rotor's performance. U.K. Saha and S. Thotla[10] conclude that the optimum number of blades is two for the Savonius rotor whether it is single, two or three stage,M.Hadi Ali [11] also conclude that the two blades Savonius wind turbine is more efficient, it has higher power coefficient under the same test condition than that of three blades Savonius wind turbine Fig.2.(a). (a) (b)
Figure.2. (a) The Cp variation with the TSR for two & three blades.[11], (b) Variation of Cp with wind speed for different aspect ratios[12]
4.2 effect of Aspect Ratio The aerodynamic performance of the Savonius rotor depends strongly on the aspect ratio (AR). N.H. Mahmoud [12] tested different configurations for aspect ratios (noted α) of 0.5, 1, 2,4,5 by keeping other parameters constant, the results show that the power coefficient increases with the rise in aspect ratio Fig.2.(b),Lately, studies with various designs of changed Savonius rotor having low ARs have been reported out. According to Kamoji [13] The rotor with an aspect ratio of 0.7 is having a maximum Cp equal to 0.21. Modi [14] also conclude that an AR of 0.77 leads to
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a maximum Cp of 0.24 However, several studies on Savonius new rotors use AR near to 1 [15], generally the use of ARs within the range of 1.5–2.0 set good results on the performance of the Savonius rotor. 4.3 Effect of overlap ratio The overlap ratio is a major parameter that influences the structure of the flow inside the rotor and consequently its aerodynamic performances, the influence of the overlap ratio has been widely investigated, however there is not an accord among the outcomes acquired in previous studies. According to Blackwell [16] the optimal value of overlap ratio is in the range of 0.1 to 0.15. J.Menet [17] indicate that the primary overlap ratio must be between 0.15 and 0.3 and the optimal value equal to 0.242.Akwa [18] has also done a detailed investigation on the effect of overlap ratio and indicate that the configuration of Savonius rotor that shows the best performance is the one where the overlap ratio equal to 0.15, which gives an averaged power coefficient equal to 0.3161 for the TSR of 1.25. 5
New design
Recently scientific research have introduced new rotor designs by adding extra sets to the conventional rotor reach a to a better performance .The following part clarifies the different new design developed: 5.1 Obstacle shielding returning blade with optimized blade shape design: The installation of obstacle plate shields partly the returning blade of a savonius turbine and that optimizes the wind direction toward the advancing blade, the new design improves the self-starting capability for Savonius rotor. While the conventional savonius turbine shows a negatives values for the static moment in some range of rotation angle, the obstacle leads to a positive static moment value at any angle. The idea of introducing an obstacle in the design of the turbine was developed later in order to specify the optimal position of the obstacle to achieve better performance. The optimal position of obstacle plate is (X1/R = -1.2383, Y1/R = -0.4539, X2/R = -1.0999 and Y2/R = 1.1770, which leads to an angle β = 100.8° fig.3.(a), this optimal configuration leads to a peak power output coefficient of 0.258 at λ= 0.8[19]. In order to reach the maximum power coefficient a complementary study has been established, the obstacle plate is kept fixed in the optimal position and they investigate the optimization of the blade shape, the optimization is used to find the best blade shape while taking into account the obstacle shielding the returning blade in the optimum position. The free design variables considered for the optimization thus describe the blade skeleton line for a constant blade thickness of 2 mm. For this purpose, six parameters are considered (X P1, YP1, XP2, YP2, XP3 and YP3, Fig.3.(b), so the optimal shape is found for following values X P1/r=0.6909, YP1/r=0.0386,XP2/r=0.3940,YP2/r=-0.6067,XP3/r=0.6389,YP3/r =0.6357 fig.3.(b).This optimization procedure is able to identify considerably better configurations than the standard Savonius turbine, leading to a relative increase of the power output coefficient by 38.9% at λ= 0.7. This positive effect is also observed for the torque coefficient. The absolute performance increase is even higher for smaller values of λ, while the highest relative increase (75.4%) is observed at λ = 1.4 [20]. 5.2 blade Curtaining design To improve the performance and increase the efficiency of Savonius rotor without changing the basic structure of the Rotor, a curtain arrangement made up from wind deflecting plates has been designed and placed in front of the rotor, there are four variables on the curtain arrangement. These are lengths of the curtain blades (l 1 and l2) and the angles of the blades (α and β) fig.3.(c) the minimum value of α has been determined as 30°which can prevent the wind force on the convex blade. The angle has been increased up to 60° with 5° increments in the study, β angle has been considered in the range of (0–30°). The lengths of the curtains have been initially adjusted to cover the effective flow field. Then, l1 and l2 lengths have been increased gradually to find the optimum lengths which generate maximum torque, power and power coefficient. Experiments have been conducted by using the arrangement of Savonius wind rotor without curtain and with three different curtains at different angles (α and β). The highest power coefficient has Been obtained with the curtain 1 arrangement (l1 =45cm, l2=52 cm, α = 45° and β= 15°) with an increase38%[21].
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(a) (a)
387
(b) (b)
(d)
(c)
(f) (g)
(e)
Fig. 3. various new design of savonius rotor: (a) ostacle shielding returning blade[19] , (b) Obstacle shielding with optimized blade shape design [20],(c) Curtain design [21]. (d) V-blade [22] , (e) quarter blade[23], (f) conveyor-deflector curtain[24] (g) combined blade[25]. Table 1: comparison of the maximum power coefficient obtained for new design of Savonius rotor Author M.H. Mohamed,D. Thévenin [19] M.H. Mohamed, D. Thévenin[20] B. D.Altan , M.Atılgan [21] H. E. Gad,A. A. Abd El-Hamid [22] S.Sharma,R. Kumar [23] M.Tartuferia,,V.D'Alessandro[24] A. Sanusi ,S.Soeparman [25] Y.X. Yao, Z.P. Tang [26] G. Kailash [27],,Ogawa [28] S.Iio , Y.Katayama[29]
new design Obstacle shielding Obstacle shield optimized blade Curtain design V-shaped blade Multiple quarter blades Conveyor-deflector curtain system Combined Blade Tower cowling Deflector plate Shield Plat
Cp max 27.3% increase from the conventional rotor 38.9% increase from the conventional rotor 38 % increase from the conventional rotor 0.37 8.89% increase from the conventional rotor 20% increase from the conventional rotor 11 % increase from the conventional rotor 0.48 0.35, 24% increase from the conventional rotor 0.47
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5.3 V-shape Blade The study includes seven shapes of modified blade in addition to the conventional Savonius rotor. The results showed that the Modify 4 fig.3 (d) rotor has the best values of average torque and average Cp at TSR up to 0.9 [22]. Conclusion The Savonius rotor has proven its performance due to its simple design, low cost and low starting torque at low wind speed despite its low efficiency caused by the negative torque applied to the returning blade, for years several researches aim to improve the design of Savonuis rotor in order to achieve better performance. This paper aims to compare several results of published articles on performance of new designs of Savonius rotor. It is intended to provide an important background for future studies on this type of wind turbine. According to this review result we conclude that over the years, the development of the shape of Savonius rotor blade remains a very promising research field in order to improve the performance of the rotor, It is perceived that research on parameters such as AR, overlap ratio and number of blade can be more studied to arrive at a satisfactory level of performance, although adding an extra set like obstacle shielding, curtain or conveyor deflector improve the performance of Savonius these developed designs of Savonius have made this rotor system very complex and dependent on the direction which represent a major drawback of this studies, in this context the search for a compromise between rotor efficiency and system simplicity is a promising area of research for future works. References.
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