Australian Journal of Basic and Applied Sciences. Rules Of Similarity For Model With Prototype Vertical Axis Wind Turbine

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1 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: AENSI Journals Australian Journal of Basic and Alied Sciences ISSN: Journal hoe age: Rules Of Siilarity For Model With Prototye Vertical Axis Wind Turbine 1 Ahed Y. Qasi, Salih Haeed, 3 Salah Abaas and 4 Hayder Talib 1,,3,4 Ministry of Industry & ineral, Alkaraa General Coany, Iraq. A R T I C L E I N F O Article history: Received 5 Aril 014 Received in revised for 8 May 014 Acceted 0 May 014 Available online 17 June 014 Keywords: Wind turbine, Vertical axis wind turbine, Siilarity, Power coefficient A B S T R A C T This aer resented a develoent focusing on VAWTs, Which the rotor axis is erendicular to the direction of the wind. It is resented the erforance of the odel oerating on the drag force having three fraes/blades cavity shae with ovable vanes, siilarity to The erforance of a siilar rototye vertical axis wind turbines having a scale ratio of 1:10. The resent odel gives the axiu ower coefficient of 0.3 at a wind seed of 8. /s and ti seed ratio of Discussed the develoent of the ower coefficient of the wind turbine varying with the test results araeters such as, ti seed ratio, angular velocity and the ower generated 014 AENSI Publisher All rights reserved. To Cite This Article: Ahed Y. Qasi, Salih Haeed, Salah Abaas and Hayder Talib. Rules Of Siilarity For Model With Prototye Vertical Axis Wind Turbine. Aust. J. Basic & Al. Sci., 8(10): , 014 INTRODUCTION Wind energy is one of the cheaest and cleanest of renewable energy technologies. It is very iortant to use this wind resource to generate electricity because wind ower is clean, quiet, and efficient. Wind ower is the conversion of wind kinetic energy into a useful for, such as echanical or electrical energy that can be harnessed for ractical use by using wind turbines. There are various tyes of wind turbines with different efficiencies. The efficiency is defined as the aount of wind kinetic catured by the wind turbines that can be successfully generated into electrical ower. Power Coefficient (C) is a ratio of the ower generated by the achine to the ower available in the wind: Wgen C (1) 3 0.5AV Where: Wgen is the ower roduced by the generator of turbine [W], ρ - Air density [kg/3], A - Swet area of the turbine [] and V- Wind seed [/s]. Betz Law clais that the highest efficiency wind turbine cannot convert ore than 59.3 % or 16/7 wind kinetic energy into echanical energy (Mathew, 006). The law states that it is the roble with nature of wind turbines, not the generator s efficiencies. In vertical axis wind turbine roelled only by drag forces, the rotor cannot rotate with ore than the wind velocity, and the ower coefficient deends on the drag coefficient of the rotor frae. Thus, the axiu ower coefficient is given by the following Equation (Kaltschitt et al., 007): C ax. 4 7 CD () The otential of wind energy conversion is huge as there is a rearkable free energy in the wind. Utilization of wind achines to yield the energy of the wind is not a new concet and it can be tracked back as far as the Chinese in 000 B.C. Early achines were utilized to u water for irrigation uroses. After that, windills were develoed for grinding grain roducts. (Ibrahi, 009) Nowadays, there are ever increasing intensive research and iroveent that are done into the harness of wind energy for electricity generation. This is due to the rising deand or need for ore efficient and caacity of wind turbines, which is one of the cleanest renewable energy resources. Corresonding Author: Ahed Y. Qasi, Ministry of Industry & ineral, Alkaraa General Coany, Iraq. Phone: ; E-ail: ayhk66@yahoo.co

2 310 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: Today, a nuber of different tyes of wind turbines exist. They can be categorized into two ain tyes, those with rotor shaft rotate around a horizontal axis and those with rotor shaft rotate around vertical axis. Horizontal axis wind turbines (HAWT) have blades ounted radially fro the rotor. The blades will rotate on axis arallel to the ground. This tye of wind turbine is the ost coon and older than the Vertical Axis Wind Turbine. The odernized wind turbines usually have two or three blades and are ainly used for large scale grid connected electrical ower generation. There are two ain tyes of VAWTs, (Which the rotor axis is erendicular to the direction of the wind) deending on the force which oerates the turbine. The first tye of VAWT is Darrieus wind turbine, which is atent at 1931, this tye was oerated by lift force; so, it has a high angular velocity and work with low starting torque. The second tye of VAWT is Savonius wind turbine, which is atent at 190, this tye was oerated by drag force; so, it has a low angular velocity and work with high starting torque. Savonius rotor is a unique fluid achine that has been studied by nuerous investigators since 190s. It can develo a relatively high torque at low rotational seeds and is chea to build, but it harnesses only a sall fraction of the wind energy incident uon it. It is sile to asseble but requires a lot of aterial in its construction (Reuke and Probert, 1991). Alications of Savonius rotor, in general, includes uing water, driving an electrical generator, roviding ventilation, and agitating water to kee stock onds ice-free during the winter (Fernando and Modi, 1989). It aears fro the literature review that there is a need to irove the erforance of a vertical axis wind turbine by iroving its ower coefficient. An attet has been ade in this regard in the resent aer by designing a new ieller tye wind turbine and evaluating its erforance by conducting exerients in a low seed wind tunnel. The Study Of Blade Ratio Effect ( Cord ): radius Weight of the frae is one of the araeters affecting on the torque, the agnitudes of torque, tangential stresses deend on the radius of action, where the agnitude of the torque roortional with the external radius. However, the weight of coonents is roortional with solidity of radius. To decrease the weight without decrease of the agnitude of torque and stresses in engineering acceted design of the hollow shaft. The size of the hollow is subjected of otiization. For silicity in industry that acceted 10% of the total torque can be neglected. The weight can be reduced by reoving soe of its area. An attet is ade to find out an equivalent area to be reoved which will reduce roughly 10% of total generated torque after its reoval. The sace to be reoved is near the shaft for two reasons. First, the facts that this area generates less torque due the short ar frae the axis of rotation. Where grows the ar stay away fro the axis of rotation and thus grow torque. And second, to allow the air ass fro all sides of the vanes thus reducing the vortices behind the vane. Figure (1) shows the wind force develoed on the length of the frae and torque diagra used to calculate the diension ratio of frae to be reoved atheatically Let b be the radius of the area A 1 to be reoved and C is the cord of the frae. Taking the hel of Figure (1), the wind force exerted on A 1 the vane is giving by: F Phb (For A 1 ) Which, h is the frae height and P is the wind ressure. Fig. 1: Force and torque diagra for frae

3 311 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: The resulting torque will be: T 1 = P.h.b²/ (3) T = P.h[(b+ C) b C ( ) ] (where, b C r ) (4) The torque T 1 acting on area A 1 to be 10% of that acting on area A of the frae, than can be writing as: T 1 = 0.1T After silification, we get: b = 0.3 r (5) C = 0.7 r (6) It eans that reoving decrease 30% fro the rojected area of the frae near the shaft, leads to decrease 9% of the total torque generated by frae rotating in the direction of the wind. Exeriental Results: The wind turbine testing used the three frae cavity vane odel. The detailed design of the resent ieller tye vertical axis wind turbine can be found in Qasi et al.(011). There are three necessary conditions for colete siilarity between a odel and rototye. The first condition is geoetric siilarity- the odel ust be the sae shae as the rototye, but ay be scaled by soe constant scale factor. The second condition is kineatic siilarity, which eans that the velocity at any oint in the odel flow ust be roortional (by a constant scale factor) to the velocity at the corresonding oint in the rototye flow. The third and the ost restrictive siilarity condition is that of dynaic siilarity. Dynaic siilarity is achieved when all forces in the odel flow scale by a constant factor to corresonding forces in the rototye flow (force scale equivalence). The scale of the odel to the rototye is one-tenth. The odel was tested in the wind tunnel with a axiu wind seed of V = 5 /s. At this scale ratio the rototye will have the diaeter of 000, with cord sizes 700 (width) and 1160 (height). The cord has three vanes of vertical location, and takes a scoo shae with a diension of 90 (width) and 1160 (height). It is necessary to deterine the seed and drag force of the wind in order to achieve siilarity between the odel at the axiu wind seed tested in wind tunnel and the rototye of the three fraes. The concet of siilarity was utilized to deterine the seed of the wind and drag force of the rototye. The air teerature of 5 o C, density ρ = 1. kg/ 3, and viscosity μ = 1.849*10-5 kg/.s are the sae for the rototye and for the odel. For low wind seed, it is acceted that coressibility of the air is negligible, and the wind-tunnel walls do not interfere with the aerodynaic drag on the odel of the wind turbine. Fro exeriental results of the roosed roeller tye wind turbine odel, the ti seed ratio (λ) varies fro to The ower coefficient is equal to at the lower value of λ. It increases to a axiu value of 0.3 at λ = 0.3 and thereafter it decreases with the increasing ti seed ratio (Qasi et al. 011). It should be noted that the decrease in C P after its axiu value is ainly due to the increase in wind velocity because the ti seed ratio does not vary uch after the axiu C P. increase in ti seed ratio after the axiu value of C P is very les but there is a dro in C P ainly due to the increase in wind velocity. The increase in λ refers to the increase in wind seed. Coaring the exeriental results with results resented in the textbooks, (Erich, 006) reorted that the axiu ower coefficient for VAWT Savonius tye is lower than 0%. (Johnson, 006) resented the axiu ower coefficient for VAWT Savonius tye after considering the iroveents suggested in soe key ublication in recent years, to be round 30% this curves results have been used extensively in the results. For the odel, the wind seed is fixed and the value of angular velocity of the rotor is calculated for the range of λ. This ste is reeated for other wind seeds and the results are shown in Table (1). It is to be ointed out that range of wind seed selected here is between 3 /s and 10 /s ainly because the axiu ower coefficient found out fro the exerient is at a wind seed of 8 /s. Table (1) also shows the values of the ower coefficients at different ti seed ratios which are indeendent of the wind seeds.

4 31 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: Table 1: Calculation of angular velocities of rotor for different wind velocities (3-10 /s) at different ti seed ratios λ C The above results are lotted to show the variation of the angular velocity with the ower coefficient for different wind velocities as shown in Figure. Fig. : ower coefficient VS angular velocity for odel at wind seed 3-10 /s Siilarity Of Model With Prototye: For "low seed" wind tunnel testing, below which the Mach nuber deendence can be neglected, the results will not be deendent on the Froude nuber and can be coared for siilarity using only the Reynolds nuber (Barlow et al., 1999). In order to coare the results obtained fro the wind tunnel with those fro other scales, it is necessary to describe the oerating conditions of each test setu in ters of the Reynolds nuber of the flow.siilarity equation is given by the equation of the Reynolds nuber in the following exression: V L V L Re Re (7) Where indices and reresent odel and rototye, resectively, L is the size of the rototye or odel, and the other araeters are as secified earlier. In addition: U L U L Re Re Where: U, U are the circuferential seeds of the corresonding rotor's eleents in odel and rototye, resectively, is the dynaic viscosity and D is the length araeter such as the diaeter of the object (Laura et al., 004). It is iossible to consider this condition for large industrial wind turbines because the odel tests would be conducted in wind tunnels at atosheric ressure and abient teerature. It results that the viscosity:

5 313 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: V U U And the receding equations can be written as: D V D (8) And D U D In addition, the circuferential seed U can be exressed in ters rotational seed N as: D N R D N D (10) In a cylindrical vessel stirred by a central rotating addle, turbine or roeller, the characteristic diension is the diaeter of the agitator D. The velocity is ND where N is the rotational seed (revolutions er in.) (Sarfaraz, 011), Then the Reynolds nuber is: N D Re This allows Eq. (7) to be written as: N D N D N D N (11) D To find the angular velocities of rototye rotor scale ratio (1/10) at different ti seed ratios, alying the sae stes of odel on the rototye wind turbine for different wind velocities (3-10 /s) the results shown in Figure (3) and Table () Table : Calculation of angular velocities of rototye rotor scale ratio (1/10) for different wind velocities (3-10 /s) at different ti seed ratios (9) λ C Fig. 3: ower coefficient VS angular velocity for rototye scale ratio (1/10) at wind seed 3-10 /s

6 314 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: Fro figure (3) across the angular velocity with wind seed to get C. And to find the value of ower we use Equation (9) or for siilarity between odel and rototye at the scale ratio (1/10) by using Eq. (10) to find the rototye ower as shown in Table (3). W C (1) 3 0.5AV W W D D (13) Table 3: Calculation of ower of rototye rotor scale ratio (1/10) for different wind velocities (3-10 /s) at different ti seed ratios λ ower 3/s ower 4/s ower 5/s ower 6/s ower 7/s ower 8/s ower 9/s ower 10/s calculate the ower for rototye wind turbine at a certain wind seed as a curved covers all range of ti seed ratio (λ) that the turbine work in the certain wind seed as shown in Figure (4), or by easure angular velocity (RPM) and across result with wind seed to find the ower as shown in Figure (5). Fig. 4: ower VS ti seed ratio for rototye scale ratio (1/10) at wind seed 3 10 /s Fig. 5: ower VS angular velocity (RPM) for rototye scale ratio (1/10) at wind seed 3 10 /s

7 315 Ahed Y. Qasi et al, 014 Australian Journal of Basic and Alied Sciences, 8(10) July 014, Pages: To calculate the axiu ower for rototye wind turbine at any wind seed, take the axiu ower coefficient and use Eq. (1) at thus wind seed. Aling that at the roose odel the axiu ower coefficient is 0.3 to find the axiu ower in all rang of wind seed. For the scale ratio (1/10), the A =.3, the W-V curve shown in Figure (6) Fig. 6: Maxiu ower VS wind seed for rototye scale ratio (1/10) The aerodynaic drag force on the wind turbine rototye is calculated by the siilarity equations in the following exression. F F V L V L (14) where, F, F is the drag force for the odel and the rototye resectively. REFERENCES Barlow, Jewel B., Willia H Rae, Jr and Alan Poe, Low-Seed Wind Tunnel Testing, 3rd Edition, John Wiley and Sons, New York, NY, ISBN Erich, H., 006. Wind Turbines: Fundaentals, Technologies, Alication, Econoics. Sringer. Gerany. Fernando, M.S.U.K. and V.J.A. Modi, Nuerical Analysis of the Unsteady Flow Past a Savonius Wind Turbine,. Journal of Wind energy and Industrial Aerodynaics, 3: Ibrahi, A.B., 009. Building a wind turbine for rural hoe. International Energy Initiative. Published by Elsevier Inc. Johnson, L. Gary, 006. Textbook Wind Energy Systes. Electronic edition, Manhattan, KS Kaltschitt, M., W. Streicher and W. Andreas, 007. Renewable Energy. Technology, Econoics and Environent, Sring, New York. Laura, K., Kucner, H. Richard, McCuen, 004. Drag Coefficient, Sonsored by the General Electric Foundation. Mathew, S., 006.Wind Energy Fundaents, Resource Analysis and Econoics. 1st ed. Sringer Grou. Qasi, A.Y., R. Usubaatov and Z.M. Zain, 011. IIUM Engineering Journal, Secial Issue, Mechanical Engineering. Qasi, A.Y., R. Usubaatov and Z.M. Zain, 011. Investigation and Design Ieller Tye Vertical Axis Wind Turbine. Australian Journal of Basic and Alied Sciences, 5(1): Reuke, P., and S.D. Probert, Slatted-blade Savonius wind-rotors, Alied Energy, 40: Sarfaraz, K. Niazi, 011. Disosable Bio-rocessing Systes, Taylor & Francis