Experimental research regarding the performance of small axial turbines

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1 Eperimental research regarding the performance of small aial turbines Sanda BUDEA*,1, Mircea Dimitrie CAZACU 1 *Corresponding author *,1 POLITEHNICA Universit of Bucharest, Facult of Energetics, Department of Hdraulics, Hdraulic Machiner and Environmental Protection Spl. Independentei 1, Bucharest, 06040, Romania sanda.budea@upb.ro*, cazacu.dimitrie@ahoo.com DOI: / Abstract: This paper continues research of the authors and presents some theoretical aspects regarding the maimum power etract from the wind turbines, the optimal incidence angle, the best twisting of the blade and eperimental research done in the laborator of Renewable Energ from the Hdraulics, Hdraulic Machineries and Environmental Engineering Department, on small aial turbines, with impeller of 500 mm and 000 mm in constructive variants: with, 4 and respectivel 8 blades. These turbines can have applications both aerodnamic - wind turbines but also hdrodnamic. It was determined the provided power, the starting / braking torque of the impeller and the power coefficients for these three tpe of turbines. From the eperimental research resulted that the best behavior had the small impeller of 500 mm, with four bladed with cp = 0.56, tested in water, than the 500 mm impeller with three blades having the power coefficient cp = 0.4, tested in air and the last impeller, with 000 mm and 8 bladed, has about cp = 0.4, tested in air too. These eperimental results are the basis of various aerodnamic and hdrodnamic applications and further research. Ke Words: aial turbine, best incidence angle, power coefficient. 1. INTRODUCTION This article presents some theoretical aspects regarding the maimum power etract from the aial turbines, the best incidence angle and the specific twisting of the blade. The article presents also the eperimental research results in the stud of the performances of three turbines with small dimensions, two of then with 500 mm diameter, with three and four blades, tested in water and also in air, and the third with 000 mm diameter, with eight blades, tested in in air at different wind velocities. The studied aial turbines have the ais in horizontal position, being of HAWT (Horizontal-ais wind turbine) tpe. To convert the kinetic energ of the fluid in maimum power we adopted aerodnamic profilated blades, which are offering the greatest etracted power and number of rotations, and consequentl the smallest size for the turbine itself and for the electrical generator. Starting from the theoretical results obtained from aerodnamic and hdrodnamic modeling and numerical analsis, three aial impellers, having the diameter of 0.5 m (two of them) and m (the third), with the airfoil profile tpe Gottingen 450 were manufactured, inspired from similar studies [1-10]. The impeller geometr had the blade pitch angle to the hub of 5 and maimum blade twisting of 7. INCAS BULLETIN, olume 5, Issue / 01, pp. 1 0 ISSN

2 Sanda BUDEA, Mircea Dimitrie CAZACU 14 Hdrodnamic and aerodnamic eperimental cases for the small impeller with diameter of 0,5 m with and 4 profilated blades were made. The best power coefficient of 0,56 was obtained in hdrodnamic tests with the impeller having 4 blades. For the case with blades the power coefficient was found to be 0,4, tested in wind. For the eperimental stud of the impeller with the diameter of m and 8 blades, we considered onl the aerodnamic behavior, as wind turbine. A power coefficient of about 0,4 was obtained. The eperimental research results are detaliated below..1 Maimum power. THEORETICAL APPROACH For a hdraulic or wind turbine rotor ver important is to etract a maimum mechanical power from the kinetic energ of the fluid stream, through the blades with a certain curvature and relative thickness, having the profiles set at the optimal incidence angle. Corresponding to figure 1, the method [5-8] consists in considering a wing chord at the peripheral radius R p of the blade at different incidence angles i o with respect to the β direction of relative velocit W and we shall consider the lift force perpendicularl of this direction, as well the drag force, which operates on the relative flow direction: c i W b lr, F c i W b lr F. (1) p F β U = R ω F W i 0 Fig. 1 elocit triangle and the components of aerodnamic resultant Proecting these two components of the hdrodnamic resultant on the turbine shaft direction, we shall obtain the aial force which loads the bearing: F a F cos F sin sin b l R c i cos c i sin, () We considered the relations = W sin = U tg. For z blades, the total aial force will be: n Fa total z b l R1 R 1 10,89r, r c i c i () INCAS BULLETIN, olume 5, Issue / 01

3 15 Eperimental research regarding the performance of small aial turbines We noted the blade section span b b, the profile depth b l (R) and the dimensionless radius b r = R/R p. For the best conversion of the kinetic energ of the fluid into maimal mechanical power at the turbine propeller, we shall cancel its partial derivative with respect to the relative angle. This wa, is obtained the optimum setting angle of the peripheral blade profile p = - i, for different profile shapes, at the incidence angles i, in order to obtain a maimum value in the scalar multiplication between the peripheral component of the resultant and the rotational velocit. Proecting the two components of the aerodnamic resultant on the rotational peripheral direction, we obtained the mechanical power epression: P UF u U cos cos F sin F cos b l c i c i The maimum power is obtained b cancelling the partial derivative: sin sin, (4) P 1 cos cos cos 0 ci c i, (5) 4 sin sin and appling the relation = U tg β at the outskirts, we obtain the optimal angular velocit: opt U opt, (6) Rptgp R tg 1 R arc tg (7) R R The power maimization was obtained onl b the selection of the optimum incidence angle [4]. P opt R F tg cos bl c sin u b l 1 R c i c i cos i c i blar c i BR c i sin sin opt cos sin The performances of aerodnamic and hdrodnamic profiles have been calculated and the maimum power and peripheral velocit was developed b the profile Gö 450 [9, 10] (table 1) for the incidence angle i = o. Table no. 1 i o c c c / c β o β p,opt o.1 The best incidence angle and the twisting of the blade For the best profile Gö 450, from the fluid mechanical power (8), cancelling its partial derivative, the relation for the best incidence angle i for an radius is obtained [6-7]: (8) INCAS BULLETIN, olume 5, Issue / 01

4 Sanda BUDEA, Mircea Dimitrie CAZACU 16 optc optc 1 c1 i i R R 0. (9) c 4c 4 c In the table, the values of the flow relative angle β(r) and the optimum incidence angle i(r) for different radius of the impeller are presented [6-8]. Channel Diameter D (mm) Relative flow angle β ( o ) Table no. Incidence angle i optim ( o ) Blade angle β p ( o ) Blade twisting δ( o ) The optimum incidence angle decreases with the increasing of the radius thus, allowing to obtain a greater velocit around the profile. The etracted mechanical power is proportional with its rd power, as in relation (9). Appling a geometrical similarit criterion for the propeller having m diameter, we obtained the values presented in table : Channel number Diameter D (mm) Table no. Relative flow angle β ( o ) Incidence angle i optim ( o ) Blade angle β p ( o ) Blade twisting δ ( o ) Starting from the theoretical studies, different impellers were manufactured: mm diameter and blades, tested in aerodnamic and hdrodnamic conditions; mm diameter and 4 blades, tested in aerodnamic and hdrodnamic conditions; mm dimeter and 8 blades, tested in aerodnamic conditions wind turbine. INCAS BULLETIN, olume 5, Issue / 01. EXPERIMENTAL RESEARCH.1 Aial turbine with propeller of 500 mm and three blades The aial micro-turbine with the geometr presented in previousl paragraph, was tested in laborator of Renewable Energ from POLITEHNICA Universit. The propeller with

5 17 Eperimental research regarding the performance of small aial turbines three blades has a power coefficient of 0,4, tested in aerodnamic conditions since the hdrodnamic conditions has c p lesser[7, 11]. In figure it can be observed the variation of the power coefficient and of the power generated b this aial turbine with the impeller of 500 mm diameter, having blades. In figure is presented the eperimental facilit with the wind tunnel and the anemometer for the air velocities. Fig. Aerodnamic tests of the propeller with blades and 0,5 m diameter - ariation of the c p and P(W) with the air flow velocities Fig. The eperimental stand with wind tunnel and the propeller with blades INCAS BULLETIN, olume 5, Issue / 01

6 Sanda BUDEA, Mircea Dimitrie CAZACU 18. Aial turbines with propeller of 500 mm and four blades During the hdrodnamic tests with this tpe of impeller an enhanced performance was obtained, given the maimum power coefficient c p = 0.56, (see figure 4). The eperimental facilit consisted in a open channel in which was placed the rotor and a hdrometric ratchet for measuring the water velocit. Fig. 4 Hdrodnamic tests of the impeller with 4 blades and 0,5 m diameter - ariation of the c p and P(W) with the water current velocit For the same propeller, in aerodnamic eperimental research the maimum value of the power coefficient was c p = 0.5, as displaed in figure 5. Fig. 5 Aerodnamic tests of the propeller with 4 blades and 0,5 m diameter - ariation of the c p and P(W) with the air flow velocit INCAS BULLETIN, olume 5, Issue / 01

7 19 Eperimental research regarding the performance of small aial turbines. Aial turbine with propeller of 000 mm and eight blades The power generated with this propeller and the corresponding power coefficients are given in figure 6. Fig. 6 Power curve and power coefficient relative to the wind velocities for the impeller with 8 blades and diameter of m Satisfactor results were obtained in this case as the power coefficient was about 0,4 and the power generated about 600 w a wind velocit of 11 m/s. the best aerodnamic behavior was found for wind velocities of 6-7 m/s. Fig. 7 The eperimental stand for the propeller with m and 8 blades INCAS BULLETIN, olume 5, Issue / 01

8 Sanda BUDEA, Mircea Dimitrie CAZACU 0 Figure 7 presents the wind tunnel for the aerodnamic tests with the propeller with m diameter and eight profiled blades. Geometrical similarl criterion and Renolds and Froude similarl criterions were complied in these theoretical analsis and eperimental studies. 4. CONCLUSIONS Starting from the theoretical results obtained from aerodnamic modeling and numerical analsis, three aial impellers, with profiled blades tpe Gottingen 450 were manufactured. In order to etract the maimum power from the fluid, the theoretical analsis shows that the rotor should have an optimal angle of incidence of. However it was revealed from our stud that the optimal values of the angle of incidence are between 1 to 14. The propeller geometr had the blade pitch angle to the hub of 5 and the maimum blade twisting specif of 7. Three different aial rotors with 500 mm diameter and blades, 500 mm diameter and 4 blades and 000 mm diameter and 8 blades were manufactured compling these features. In the eperimental research were obtained ver good results for the impeller with 4- blades (c p = 0,56 tested in hdrodnamic conditions, at a water velocit of 0,6 m/s and c p =0.5 tested in aerodnamic conditions, at a wind velocit of 6-7 m/s. Also satisfactor results were obtained for the other two propellers. Renolds and Froude similarl criterions and geometrical similarl criterion were respected during these studies. These eperimental results represent the basis for future research on various aerodnamic and hdrodnamic applications. REFERENCES [1] Н. М. Щапов, Турбиное Оборудование Гидроэлектростанций, ГОСЭНЕРГОИЗДАТ, Москва- Ленинград, 1955, 4-5. [] ***, Maшинocтрoениe, Энциклoпeдичeский Спрaвoчник, ol. 1, Moсквa, 1949, [] D. Pavel. Maşini hidraulice. ol.1, Energetics State Publ. House, Bucharest, [4] M. D. Cazacu, A. Ciocânea, Determinarea unghiului de aşezare β optimum pentru paletele turbinelor eoliene cu a orizontal, Zilele Hidraulicii 98, Conf. Wind Engineering, Mai 1998, Technical Universit of Civil Engineering, Bucharest, [5] M. D. Cazacu, The maimization of the propulsion force for an aircraft or ship propeller, The 0-th Caius Iacob Conference Fluid Mechanics and its Technical Applications, Bucharest, 5-6 November 005, CD Proceeding. [6] M. D. Cazacu, Optimization of the aial propulsion force, The 1-th Caius Iacob Conference on Fluid Mecanics and its Technical Application, 19-1 oct. 006, Buletin of Transilvania Univ. Brasov, ol.1(48), serie B 1 Mathematics, Informatics, Phsics, [7] M. D. Cazacu, S. Nicolaie, Micro-Hdraulic turbine for run-of-river power station, Conferinta hidroenergeticienilor din Romania, Dorin Pavel 00. [8] S. Budea, M. D. Cazacu, elocit spectrum in aial relative motion of wind turbine, CIEM 011, ISSN [9] ***, Hütte Des Ingenieurs Taschenbuch I, 6. Auflage. Berlin, erlag von Wilhelm Ernst & Sohn, [10] ***, Hütte I Manualul Inginerului, Publishing House AGIR, Bucharest, 1947, [11] M. D. Cazacu, S. Budea, Noi tehnologii de conversie a energiilor si de protectie a mediului, Ed. Politehnica Press, 008, ISBN , pag INCAS BULLETIN, olume 5, Issue / 01