Available online at www.sciencedirect.com
ScienceDirect Energy Procedia 61 (2014) 1275 – 1278
The 6th International Conference on Applied Energy – ICAE2014
The design and flow simulation of a power-augmented shroud for urban wind turbine system K.H. Wong a, W.T. Chong a, *, H. T. Yap a, A. Fazlizan a, W.Z.W. Omar b, c, S.C. Poh a, F.B. Hsiao d a
c
Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia b Centre of Electrical Energy Systems, Universiti Teknologi Malaysia, 81310 UTM, Johor Bahru, Malaysia Aeronautical, Automotive and Offshore Engineering Department, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310 UTM, Johor Bahru, Malaysia d Institute of Aeronautics and Astronautics, National Cheng Kung University, Tainan 70101, Taiwan ROC
Abstract Recently, there are small wind turbine developments which are suitable for urban and suburban application. However, the efficiency of the wind turbine is the main concern for all researchers due to the uncertainty of wind speed and wind direction in urban area. In this paper, a new power augmented shroud integrated with vertical axis wind turbine (VAWT) is introduced. This power augmented shroud is able to improve the performance of the VAWT significantly by increasing the wind speed. It also channels the flow to better angle of attack for the VAWT and reduces the negative torque of the wind turbine. Hence, it improves the self-starting behaviour of the VAWT, and increases the coefficient of power. The numerical method is used to simulate the wind flow for the power augmented shroud with a single bladed NACA 0015 airfoil VAWT by commercial computational fluid dynamic (CFD) software, ANSYS FLUENT 14.0. In this 2D simulation, the shear stress transport (SST) k-ω turbulence model with the sliding mesh method was used with the tip speed ratio of 5.1 for the wind turbine. The result was verified by re-simulating the experiment published by the Sandia National Laboratories. The simulation result shows that the new design of power augmented shroud is able to increase the coefficient of power significant for the VAWT which is about 147.1% compared to the bare VAWT. Therefore, for urban area application, this power augmented shroud can improve the low efficiency problem for the VAWT. © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license © 2014 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/3.0/). Selection and/or peer-review under responsibility of ICAE Peer-review under responsibility of the Organizing Committee of ICAE2014
Keywords: urban wind energy system; omni-directional-guide-vane; vertical axis wind turbine; computational fluid dynamics; Shrouded wind turbine; wind turbine performance
* Corresponding author. Tel.: +60 12 7235038; fax: +60 3 79675317. E-mail addresses:
[email protected],
[email protected] (W.T. Chong),
[email protected] (A. Fazlizan)
1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 doi:10.1016/j.egypro.2014.11.1080
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1. Introduction Wind energy has been used since hundreds years ago. Due to the energy demand increase and the depletion of fossil fuel, this clean technology has been developing rapidly. For urban area, because of the unsteady wind flow, some of the wind turbines utilize stator vanes to further increase the efficiency. Sistan wind mill system which is driven by drag force with additional wing wall, top and bottom disk shows increase in the efficiency of the turbine [1]. Similarly, Yao et al. used a drag driven VAWT system with additional tower cowling which consists of eight baffles plates evenly distributed axially to the drag type Savonius VAWT [2]. The Zephyr turbines used stator vanes distributed evenly with reversed winglets and increase the power generated. These stator blades reduce the turbulence flow hence decrease the aerodynamic loading on the blade [3]. Chong et al. has developed the power augmented guide vane (PAGV) which further improved to become the omni-direction guide vane (ODGV). This ODGV orients the inlet air and increase the wind speed to the VAWT blades, hence improves the VAWT self-starting behaviour where it improves the cut in speed, and increases the operating hour. The design of the guide vane can minimize the negative torque created on the lift type wind turbine [4]. 2. Methodology 2.1 Design of power-augmented shroud This paper presents the design of the power augmented shroud which is known as the new ODGV that can increase the coefficient of torque and the coefficient of power. Figure 1(a) shows the original ODGV design whereas Figure 1(b) is the new ODGV design. Both the designs have four pairs of guide vanes, and each pairs of the guide vanes are tilted at angle 20o, and 55o. The outer diameter of the ODGV is twice of the VAWT rotor diameter. For the new design ODGV, the guide vanes are divided into two segments with same length and bent at 10o angle.
Figure 1: a) Original ODGV design
b) New ODGV design
2.2 Numerical flow simulation The simulation was verified by re-simulating the NACA 0015 airfoil single bladed VAWT which accomplished by Oler et al. published by the Sandia National Laboratories [5]. According to the Oler’s experiment, a straight-single-bladed rotor with NACA 0015 was built, and the water was used as the working fluid to facilitate the relatively low frequency measurements while working at appropriate blade Reynolds numbers. The experiment parameter shows in Table 1.
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Table 1: Oler’s experiment parameter [4, 5] Parameter
Value
Parameter
Value
Chord length, c (m)
0.1524
Inlet velocity, v (m/s)
0.091
Rotor tip speed, RZ (m/s)
0.457
Rotor radius, R (m)
0.61
Reynolds number, Re
67,000
Width, W (m)
5
Tip speed ratio, TSR
5.1
Length, L (m)
10
2.3 Geometry modelling, mesh & computational condition of ODGV In this simulation, there are two geometry models hence two meshes were created. The VAWT space as shown in Figure 2(a) and the tunnel space as shown in Figure 2(b). For the VAWT space, it consists of the single blade NACA 0015 airfoil. The VAWT space was divided to 3 regions, which were the airfoil space, subgrid, and the main grid. Whereas for the tunnel space, it was meshed according to the Oler’s experiment tunnel dimensions with the ODGV was located at the center.
Figure 2: a) Airfoil mesh
b) Tunnel mesh
The simulation was set to be pressure-based, transient and according to the properties of water. SST k-
Z model was applied as the turbulence model and the rotational sliding mesh technique is used to
simulate the motion of the blade. The SIMPLE Pressure-velocity coupling and the second order of upwind discretization scheme were chosen for the simulation. The non-dimensional coefficient of torque, Ct data which was produced on the airfoil blade was captured for every 10 degree azimuth angle. The data were being averaged as the average coefficient of torque, Ct,avg. 3. Results and discussions The torque coefficient versus azimuth angle that was captured from the simulation is plotted and compared to the Oler’s experiment data at TSR 5.1 (inlet velocity, v = 0.091m/s). From the simulation results, it demonstrated a good agreement between the bare VAWT and the Oler’s experiment data as shown in Figure 3. When compared with Chong et al. simulation on the original ODGV design integrated with VAWT [4], the simulation result also shows similar pattern. Figure 3 shows that the ODGV can improve the Ct significantly, moreover, the new ODGV reduces the negative torque at the second half cycle and further improves the Ct. The result for the simulation is summarized in Table 2.
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Figure 3: Coefficient of torque versus azimuth angle for bare VAWT, VAWT with original ODGV and VAWT with new ODGV Table 2: Comparison of coefficient of torque and coefficient of power VAWT
With original ODGV
With new ODGV
Average Coefficient of Torque, Ct,avg
0.2158
0.4052
0.5333
Coefficient of Power, CP
0.1375
0.2581 (+87.7%)
0.3398 (+147.1%)
4. Conclusion To conclude, the new ODGV design that is integrated with VAWT is appropriate to be used in urban area where the wind speed and direction is inconsistent. The design can reduce the cut in speed, so that the VAWT has a better self-starting behaviour, hence a longer operating hour. The coefficient of power increases about 31.65% compared to original ODGV design. When compared to the bare VAWT, it is about 147.1% improvement. Acknowledgements Sincere gratitude is dedicated to Faculty of Engineering, University of Malaya, and the Malaysian Ministry of Education (KPM) for the research grants allocated which are the University of Malaya Research Grant (RP015C-13AET) and Fundamental Research Grant Scheme (FP053-2013B). References [1]Müller, G., Jentsch, M. F., & Stoddart, E. (2009). Vertical axis resistance type wind turbines for use in buildings. Renewable Energy, 34(5), 1407-1412. [2] Yao, Y. X., Tang, Z. P., & Wang, X. W. (2013). Design based on a parametric analysis of a drag driven VAWT with a tower cowling. Journal of Wind Engineering and Industrial Aerodynamics, 116(0), 32-39. [3] Pope, K., Rodrigues, V., Doyle, R., Tsopelas, A., Gravelsins, R., Naterer, G. F., & Tsang, E. (2010). Effects of stator vanes on power coefficients of a zephyr vertical axis wind turbine. Renewable Energy, 35(5), 1043-1051. [4] Chong, W. T., Fazlizan, A., Poh, S. C., Pan, K. C., Hew, W. P., & Hsiao, F. B. (2013). The design, simulation and testing of an urban vertical axis wind turbine with the omni-direction-guide-vane. Applied Energy 112 (2013), 601-609. [5] Oler, J. W. S., J.H.; Graham,B.J.Im,G.H. (1983). Dynamic Stall Regulation of the Darriues Turbine. Sandia National Laboratories (SAND 83-7029 UC-261), Albuquweque, New Mexico.
Biography Dr. Chong Wen Tong is a senior lecturer in University of Malaya. Dr. Chong has published more than 40 technical papers and filed 9 intellectual property rights on renewable energy research. His love for innovation has seen him win many prestigious awards and medals in international events.
