Performance Analysis of a Water Savonius Rotor: Effect of the Internal Overlap

Ibrahim Mabrouki, Zied Driss, Mohamed Salah Abid

  Open Access OPEN ACCESS  Peer Reviewed PEER-REVIEWED

Performance Analysis of a Water Savonius Rotor: Effect of the Internal Overlap

Ibrahim Mabrouki1, Zied Driss1,, Mohamed Salah Abid1

1Laboratory of Electro-Mechanic Systems (LASEM), National School of Engineers of Sfax (ENIS), University of Sfax, B.P. 1173, Road Soukra km 3.5, 3038 Sfax, TUNISIA

Abstract

The water Savonius rotor is classified as a vertical axis water rotor like the Darrieus, Gyromill or H-rotor. The advancing blade with concave side facing the water flow would experience more drag force than the returning blade, thus forcing the rotor to rotate. In this work, we are interested on the study of the of the internal overlap effect of a water Savonius rotor. The experimental results is developed using a hydraulic test bench. The test bench consists on an intake, a control gate, a penstock, a canalization, a test section, an outflow and a pump. A detailed description of the global characteristics is presented such as power, dynamic torque, power and its coefficients.

At a glance: Figures

Cite this article:

  • Mabrouki, Ibrahim, Zied Driss, and Mohamed Salah Abid. "Performance Analysis of a Water Savonius Rotor: Effect of the Internal Overlap." Sustainable Energy 2.4 (2014): 121-125.
  • Mabrouki, I. , Driss, Z. , & Abid, M. S. (2014). Performance Analysis of a Water Savonius Rotor: Effect of the Internal Overlap. Sustainable Energy, 2(4), 121-125.
  • Mabrouki, Ibrahim, Zied Driss, and Mohamed Salah Abid. "Performance Analysis of a Water Savonius Rotor: Effect of the Internal Overlap." Sustainable Energy 2, no. 4 (2014): 121-125.

Import into BibTeX Import into EndNote Import into RefMan Import into RefWorks

1. Introduction

Savonius rotor is a unique fluid-mechanical device that has been studied by numerous investigators since 1920s. Applications for the Savonius rotor have included pumping water, driving an electrical generator, providing ventilation, and agitating water to keep stock ponds ice-free during the winter [1, 2, 3, 4]. Savonius rotor has a high starting torque and a reasonable peak power output per given rotor size, weight and cost, thereby making it less efficient. From the point of aerodynamic efficiency, it cannot compete with high-speed propeller and the hydro-kinetic turbine electricity generation is mainly aimed for rural use at sites remote from existing electricity grids. It is a useful tool for improving the quality of life of people in these locations and for stimulating local economies. These rotors also can be considered for the wide variety of application like tides, marine currents, channel flows and water flows from industrial processes. Different designs of water current rotor are available for the extraction of energy from the river water or canals. Based on the alignment of the rotor axis with respect to water flow, two generic classes exist. They are horizontal axis turbine (axial turbines) and vertical axis turbine (cross flow turbines). Horizontal axis turbines are mainly used for extraction of the ocean energy. These turbines are expensive for small power applications. Vertical turbines generally used for small scale power generation and these are less expensive and required less maintenance compared to horizontal axis water turbines. Savonius rotor, helical turbine, Darrieus turbine and H-shaped Darrieus are commonly used vertical axis turbines. Various types of water current turbines are being installed and tested worldwide for various ranges of powers. GCK technology limited (USA), installed a Gorlov helical water turbine (diameter of 1 m and height of 2.5 m) in the Uldolomok Strait off the coast of Korea. Similarly Verdant Power Ltd. (USA) installed a three bladed horizontal axis water turbine as free flow turbine in east river New York [5]. Alternative Hydro Solutions Ltd. in Ontario has developed vertical axis turbines specifically meant to harness the water energy from river [6]. Literature suggests that there is a gaining of popularity for water turbines [7, 8, 9]. Horizontal axis turbines are common in tidal energy converters and majority of marine current turbines are horizontal axis turbine [10]. They are very similar to modern day wind turbines from design and structural point of view. In the vertical axis turbines domain, the Darrieus turbines, Savonius turbine and Gorlov helical water turbines are generally used. The Gorlov turbine has the blades of helical structure. Gorlov [11] proposed a new helical turbine to convert kinetic energy of flowing water into electrical or mechanical energy. Many researchers have adopted various techniques to maximize the performance and improve the starting torque characteristics of Savonius turbine with wind as working medium. These include use of guide vanes, V-plate deflector [12], deflector plate [13, 14] and blade with flat and circular shielding [15]. Some of these techniques require change in design of blade and other involves supplementary devices addition to the system. For example, Mohamed et al. [16] carried out a numerical analysis for identifying the optimum shielding of the returning blade of a Savonius wind rotor. Two dimensional numerical investigations were carried out using OPAL (Optimizing Algorithms) along with commercial CFD package FLUENT at a fluid velocity of 10 m/s and a tip speed ratio of 0.7. Investigation on the modified Savonius rotor (with shaft) reported by Modi and Fernando [17] was an effort in the direction of improvement of performance of Savonius wind turbine by changing the shape of the blade. Modified Savonius rotor with shaft was reported to have a maximum coefficient of power around 0.32. However, these tests were based on closed wind tunnel testing and coefficient of power was obtained by extrapolation. Kamoji et al. [18] investigated the performance of modified forms of conventional rotors with and without central shaft between the end plates.

2. Materials and Method

The used hydrodynamic test bench consists on an intake, a control gate, a penstock, a canalization, a test section, an outflow and a pump. The collector is a parallelepiped where the water flow inside a square tank located above the test section shape on a closed circuit (Figure 1). In this section, we are interested on the study of the internal overlap effect of a water Savonius rotor. This rotor consists of two buckets of diameter d=100 mm and height H=200 mm. It is assembled on a common axis and secured with a screw nut at an angle of 180° (Figure 2). Particularly, we have considered the internal overlap equals to (e-e')/d=0, (e-e')/d=0.2 and (e-e')/d=0.3 (Figure 3). In this work, the experimental study involved the rotation of the Savonius water rotor. Experimental tests for the determination of global characteristics such as the power, the dynamic torque, and its coefficients required the use of the hydrodynamic test bench. Otherwise, the test bench should be equipped with a specific instrumentation for the development of various experimental tests necessary in the laboratory scale. To achieve this goal, we use a permanent magnet dynamo creating a constant magnetic flux through the coil of the rotor, driven by the turbine rotation. The flux variation undergoes by rotating the coil creates a voltage proportional to the rotational speed. Why the higher water flow increases, the turbine rotates faster, and the generated current increases. By connecting the resistor with the multi-meter in the output of the generator, the generator is rotated by the dynamometer. For a same rotational speed imposed by the dynamometer, we change the electrical resistance and we measure the current supplied by the generator and the rotational speed of the Savonius rotor. Indeed, the dynamic torque and the power can be deduced.

3. Experimental Results

3.1. Power

Figure 4 shows the variation of the power in function of the rotation speed for different internal overlaps equals to (e-e')/d=0, (e-e')/d=0.2 and (e-e')/d=0.3. These curves are superimposed on the same scale. These results are obtained at a speed water equal to V=2.45 m.s-1 corresponding to a Reynolds number equal to Re=588300. According to these results, these curves have a parabolic shape. Moreover, these results show that the internal overlap has a direct effect on the presentation of these curves. In fact, we find that the power reaches the most important values for the internal overlap (e-e')/d=0.3. With the decrease of the internal overlap, a gradual decrease of the power is then reported. In fact, it has been noted that the maximum value of the power is equal to P=19.28 W. It is obtained in the case of an internal overlap equal to (e-e')/d=0.3 for a rotation speed equal to Ω=737 rpm. With the decrease of the internal overlap, we find that the extremum characteristic decreases on value. For example, for the internal overlap (e-e')/d=0 the maximum value of the power is equal to P=15.05 W for a rotation speed Ω=685 rpm. The increase of the power value is due to the decrease of the Savonius rotor diameter. This implies that when the diameter decreases the Savonius rotor power decreases also.

Figure 4. Variation of the power P for different internal overlap
3.2. Dynamic Torque
Figure 5. Variation of the dynamic torque Md for different internal overlaps

Figure 5 shows the variation of the dynamic torque Md in function of the speed of rotation for different internal overlaps equals to (e-e')/d=0, (e-e')/d=0.2 and (e-e')/d=0.3. These curves are superimposed on the same scale. These results are obtained at a speed water equal to V=2.45 m.s-1 corresponding to a Reynolds number equal to Re=588300. According to these results, these curves have a parabolic shape. Moreover, these results show that the internal overlap has a direct effect on the presentation of these curves. In fact, we find that the dynamic torque reaches the most important values for an overlap (e-e')/d=0.3. With the internal overlap decrease, a gradual decrease of the dynamic torque Md is then reported. In fact, it has been noted that the maximum value of the dynamic torque is equal to Md=0.25 N.m. It is obtained in the case of an internal overlap (e-e')/d=0.3 for a rotation speed equal to Ω=737 rpm. With the decrease of the internal overlap, we find that the extremum characteristic decreases of value. For the internal overlap (e-e ')/d=0, the maximum value of the dynamic torque is equal to Md=0.21 N.m for a rotation speed Ω=685 rpm. The increase of the dynamic torque value Md is due to the decrease of the Savonius rotor diameter. This implies that when the diameter decreases, the dynamic torque of the Savonius rotor decreases also.

3.3. Power Coefficient

Figure 6 shows the variation of the power coefficient Cp in function of the specific speed for different internal overlaps equals to (e-e')/d=0, (e-e')/d=0.2 and (e-e')/d=0.3. These curves are superimposed on the same scale. These results are obtained at a water speed equal to V=2.45 m.s-1. In these conditions, the Reynolds number is equal to Re=588300.

According to these results, these curves have a parabolic shape. Moreover, these results show that the internal overlap has a direct effect on the presentation of these curves. In fact, we find that the power coefficient reaches the most important value for the overlap equal to (e-e')/d=0.3. With the decrease of the internal overlap, a gradual decrease of the power coefficients values Cp is then reported. In fact, it has been noted that the maximum value of the power coefficient is equal to Cp=0.327. It is obtained in the case of an internal overlap equal to (e-e')/d=0.3 for a specific speed equal to λ=2.51. With the decrease of the internal overlap, we find that the extremum characteristic decreases of value. For the internal overlap (e-e')/d=0, the maximum value of the power coefficient is equal to Cp=0.215 for a specific speed λ=3.027. The increase of the power coefficient value Cp is due to the decrease of the Savonius rotor diameter. This implies that when the diameter increases, the Savonius rotor efficiency increases also.

Figure 6. Variation of the power coefficients Cp for different internal overlap.
3.4. Dynamic Torque Coefficient

Figure 7 shows the variation of dynamic torque coefficient in function of the specific speed for different internal overlap equal to (e-e')/d=0, (e-e')/d=0.2 and (e-e')/d=0.3. These curves are superimposed on the same scale. These results are obtained at a speed water equal to v=2.45 m.s-1 corresponding to a Reynolds number equal to Re=588300.

According to these results, these curves have a parabolic shape. Moreover, these results show that the internal overlap has a direct effect on the presentation of these curves. In fact, we find that the dynamic torque coefficient reaches the most important values for an overlap (e-e')/d=0.3. With the decrease of the internal overlap, a gradual decrease of the of dynamic torque coefficient CMd is then reported. In fact, it has been noted that the maximum value of the dynamic torque coefficient is equal to CMd=0.26. It is obtained in the case of an internal overlap (e-e')/d=0.3 for a specific speed equal to λ=2.51. With the decrease of the internal overlap, we find that the extremum characteristic decreases of value. For the internal overlap (e-e')/d=0, the maximum value of the dynamic torque coefficient is equal to CMd=0.155 for a specific speed λ= 3.02. The increase of the dynamic torque coefficient value CMd is due to the decrease of the Savonius rotor diameter. This fact implies that when the diameter decreases the dynamic torque coefficient Savonius rotor decreases also.

Figure 7. Variation of the dynamic torque coefficient CMd for different internal overlaps

4. Conclusion

In this paper, we focalise our attention on the study of the overlap effect on the global characteristics of the water Savonius rotor. Particularly, we have studied the variation of the power, the dynamic torque, and its coefficients depending on the rotational and the specific speed. In this work, we confirm that the global characteristics of the Savonius rotor increases in the used test section with the increase of the overlap.

In the future, we suggest the deflector addition to improve the rotors performance.

Acknowledgement

The authors would like to thank the Laboratory of Electro Mechanic Systems (LASEM) members for the financial assistance.

Nomenclature

CMd dynamic torque coefficient

Cp power coefficients

d rotor diameter [mm]

H Rotor height [mm]

Md Dynamic torque [N.m]

P power [W]

V Water speed [m/s]

ρ Density of the water [kg.m-3]

µ Dynamic viscosity [m.s-2]

λ specific speed

Ω Rotational frequency [rad.s-1]

Acknowledgement

The authors would like to thank the Laboratory of Electro-Mechanic Systems (LASEM) members for the financial assistance.

References

[1]  Modi VJ, Roth NJ, Pittalwala A. Blade configuration of the Sovonius rotor with application to irrigation system in Indonesia. In: Proceedings of 16th intersociety energy conversion engineering conference, Atlanta, GA, USA, 1981.
In article      
 
[2]  Clark RN, Nelson V, Barieau RE, Gilmore E. Wind turbines for irrigation pumping. Journal of Energy 1981; 5: 104-8.
In article      CrossRef
 
[3]  Modi VJ, Fernando MSUK, Yokomizo T. An integrated approach to design of a wind energy operated integrated system. ASME/AIAA Paper No. 98-0041, 1998.
In article      
 
[4]  Vishwakarma R. Savonius rotor wind turbine for water pumping—an alternate energy source for rural sites.Journal of Institution of Engineers (India) 1999; 79: 32-4.
In article      
 
[5]  Rourke FO, Boyle F, Reynolds A. Renewable energy resources and technologies applicable to Ireland. Renew Sust Energy Rev 2009; 13: 1975-84.
In article      CrossRef
 
[6]  Khan MJ, Iqbal MT, Quaicoe JE. River current energy conversion systems: progress, prospects and challenges. Renew Sust Energy Rev 2008; 12: 2177-93.
In article      CrossRef
 
[7]  Khan MJ, Bhuyan G, Iqbal MT, Quaicoe JE. Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river andtidal applications: A technology status review. Appl Energy 2009; 86: 1823-35.
In article      CrossRef
 
[8]  Anyi M, Kirke B. Evaluation of small axial flow hydrokinetic turbines for remote communities. Energy Sust Dev 2010; 14: 110-6.
In article      CrossRef
 
[9]  Guney MS, Kaygusuz K. Hydrokinetic energy conversion systems: a technology status review. Renew Sust Energy Rev 2010; 14:2 996-3004.
In article      
 
[10]  Rourke FO, Boyle F, Reynolds A. Marine current energy devices: current status and possible future applications in Ireland. Renew Sust Energy Rev 2010; 14: 1026-36.
In article      CrossRef
 
[11]  Gorlov AM. Helical turbines for the Gulf stream: conceptual approach to design of a large scale floating power farm. Marine Technol 1998; 35: 175-82.
In article      
 
[12]  Shaughnessy BM, Probert SD. Partially-blocked Savonius rotor. Appl Energy 1992; 43: 239-49.
In article      CrossRef
 
[13]  Huda MD, Selim MA, Sadrul Islam AKM, Islam MQ. The performance of an Sshaped Savonius rotor with a deflecting plate. RERIC Int Energy J 1992; 14 (1): 25-32.
In article      
 
[14]  Ogawa T, Yoshida H, Yokota Y. Development of rotational speed control systems for a Savonius-type wind turbine. J Fluids Eng 1989; 111: 53-8.
In article      CrossRef
 
[15]  Alexander AJ, Holownia BP. Wind tunnel tests on a Savonius rotor. J Ind Aerodynam 1978; 3: 343-51.
In article      CrossRef
 
[16]  Mohamed M, Janiga G, Pap E, Thevenin D. Optimisation of Savonius turbinesusing an obstacle shielding the returning blade. Renew Energy 2010; 35: 2618-26.
In article      CrossRef
 
[17]  Modi VJ, Fernando MSUK. On the Performance of the Savonius Wind Turbine. JSolar Energy Eng 1989; 111: 71-81.
In article      CrossRef
 
[18]  Kamoji MA, Kedare SB, Prabhu SV. Experimental investigations on single stage modified Savonius rotor. Appl Energy 2009; 86 (7-8): 1064-73.
In article      CrossRef
 
[19]  I. Mabrouki, Z. Driss and MS. Abid, “Influence of the hight on Characteristics of Savonius Hydraulic Turbine,” International Conference on Mechanics and Energy ICME’2014, March 18-20, 2014, Monastir, TUNISIA.
In article      
 
[20]  I. Mabrouki, Z. Driss and MS. Abid, “Computer modeling of 3D turbulent free surface flow in a water channel with and without obstacle,” International Conference on Mechanics and Energy ICME’2014, March 18-20, 2014, Monastir, TUNISIA.
In article      
 
[21]  I. Mabrouki, Z. Driss and MS. Abid, “Hydrodynamic test bench design for the study of the water turbines,” International Symposium on Computational and Experimental Investigations on Fluid Dynamics CEFD’2013, March 18-20, 2013, Sfax, TUNISIA.
In article      
 
[22]  I. Mabrouki, Z. Driss and MS. Abid, “Experimental investigation of the height effect of water Savonius rotors,” International journal of mechanics and application, 2014: 4: 8-12.
In article      
 
comments powered by Disqus
  • CiteULikeCiteULike
  • MendeleyMendeley
  • StumbleUponStumbleUpon
  • Add to DeliciousDelicious
  • FacebookFacebook
  • TwitterTwitter
  • LinkedInLinkedIn