本研究的目的是在探討一個具有外罩的水平軸風力渦輪的設計方法，使能夠達到更高的功率輸出。研究採用數值方法來模擬不含轉子的外罩及外罩式風力渦輪(Diffuser Augmented Wind Turbine，簡稱DAWT)的定常流場，並探討外罩長徑比、外罩直徑比和葉片數對DAWT空氣動力性能的影響，且藉由流場分析完整的解釋DAWT功率大幅提升的物理現象。使用的數值計算工具為ANSYS CFX計算流體力學(Computational Fluid Dynamics，簡稱CFD)軟體，為了驗證數值計算工具的準確度，研究中首先針對美國國家可再生能源實驗室(National Renewable Energy Laboratory，簡稱NREL) Phase VI Rotor二葉片的水平軸風力渦輪(Horizontal Axis Wind Turbine，簡稱HAWT)進行計算分析，並與NREL風洞實驗的數據比較，除了在葉片表面發生氣流分離過渡時，數值模擬與實驗的結果有些微差異外，整體而言，數值模擬與實驗的結果相當吻合。
在不含轉子的外罩的數值模擬中，以5種外罩長徑比及6種外罩直徑比組合成30種不同的物理模型進行流場分析，從流場的壓力分佈發現外罩出口產生一低壓區，氣流加速流入外罩內，並增加通過轉子位置的質流量，這是造成DAWT功率提升的主要物理機制。
在DAWT的數值模擬中，以不含轉子的外罩和三葉片轉子組合成30種不同的物理模型進行流場分析，葉片的幾何外型與NREL Phase VI Rotor的葉片相同，其結果顯示外罩長徑比1.0和外罩直徑比2.0的DAWT，其基於轉子掃掠面積的功率係數等於0.97，為做為比較參考的無外罩風力渦輪的2.2倍，外罩長徑比0.25和外罩直徑比1.2的DAWT，其基於外罩出口面積的功率係數等於0.48，為無外罩風力渦輪的1.1倍，證實增加一適當的外罩於現有的HAWT轉子周圍可大幅提高輸出功率。從數值模擬的結果發現DAWT的最大功率係數隨軸向誘導因子變化的趨勢與一維動量理論一致。從流場的分析顯示DAWT靠近葉尖的壓力面與吸力面的壓差較大，產生的葉尖渦流強度較無外罩風力渦輪大，但DAWT的外罩對葉尖渦流的抑制效果非常顯著，因此DAWT的葉尖渦流消散較無外罩風力渦輪快。
研究中也探討了葉片數對DAWT空氣動力性能的影響，結果顯示增加葉片數會造成氣流的阻抗增加，進而降低通過轉子的質流量，且葉片數對DAWT的阻抗效應比對HAWT來得大，但葉片數對功率係數的影響則需進一步考量葉片的幾何外型，研究結果顯示當軸向誘導因子介在0.25與0.4之間會有較佳的最大功率係數。
本研究DAWT的數值模擬結果證實DAWT的功率係數高於HAWT，經由流場分析完整的解釋DAWT功率輸出大幅提升的物理機制，並提出一個DAWT空氣動力設計依循的方向，使能夠達到更高的功率輸出。在成本及功率係數的考量下，DAWT的外罩可選用外罩長徑比0.25和外罩直徑比1.4；在有限空間及功率係數的考量下，DAWT的外罩可選用外罩長徑比0.25～0.5和外罩直徑比1.2；若只考量功率係數DAWT的外罩可選用外罩長徑比大於等於1和外罩直徑比大於等於1.8，而在決定DAWT轉子的葉片數時，需同時考量葉片幾何外型，使得轉子操作在額定葉尖速度比時，軸向誘導因子能介在0.25與0.4之間，從研究結果可知若葉片採用較大弦長和較小槳距角分佈的設計，則轉子應採用較少的葉片數。

The purpose of this study is to explore the design method of a horizontal axis wind turbine (HAWT) with a diffuser to increase power output. This study used numerical methods to simulate steady flow fields of diffusers with no rotor and diffuser augmented wind turbines (DAWTs), and explored the effect of diffuser length-diameter ratio, diffuser diameter ratio, and the number of blades on DAWT aerodynamic performance. Furthermore, it conducted flow field analyses to explain the physical phenomenon of considerable enhancement of DAWT power. The numerical tool used in this study was ANSYS CFX computational fluid dynamics (CFD) software. To verify the accuracy of the numerical tool, this study first calculated and analyzed the Phase VI Rotor two-bladed HAWT of the U. S National Renewable Energy Laboratory (NREL), and compared the results with the NREL wind tunnel experimental data. Overall, the numerical simulation results and experimental data were consistent, except for slight differences for the laminar-turbulent transition on the suction side of the blade.
In the numerical simulation of diffusers with no rotor, this study analyzed the flow field using 30 different physical models, consisting of 5 diffuser length-diameter ratios and 6 diffuser diameter ratios. The flow field analysis found that, the main physical mechanism causing the enhancement of DAWT power is the low pressure area of the diffuser. When the airflow is accelerated into the diffuser, the mass flowing through the rotor plane is increased.
In the DAWTs numerical simulation, the flow field analysis used 30 physical models, consisting of 30 different diffusers with no rotor and a three-bladed rotor. The blade geometry was the same as the NREL Phase VI Rotor blade. The numerical results showed that DAWT (diffuser length-diameter ratio=1.0,diffuser diameter ratio=2.0) has the maximum power coefficient based on the rotor sweep area of 0.97, which was 2.2 times of HAWT (Baseline). DAWT (diffuser length-diameter ratio=0.25,diffuser diameter ratio=1.2) has the maximum power coefficient based on the diffuser exit area of 0.48, which as 1.1 times of HAWT (Baseline). The above results confirmed that placing an appropriate diffuser around the current HAWT rotor could considerably enhance power output. Moreover, the trend of the maximum power coefficient changing with the axial induction factor and the trend of the momentum theoretical analysis were consistent. Flow field analysis suggested that the pressure difference between the pressure side and the suction side near the blade tip of DAWT was relatively greater, thus, the resulting blade tip vorticity was greater than that of wind turbines with no diffuser. However, the diffuser had a very significant suppressing effect on the blade tip vortex, thus, the DAWT blade tip vortex dissipation was faster than that for wind turbines with no diffuser.
This study also explored the effect of the number of blades on DAWT aerodynamic performance, and found that the increasing number of blades caused increased airflow resistance, thereby reducing the mass flowing through the rotor. Moreover, the blockage effect of the number of blades on DAWT was greater than that of HAWT; however, the effect of the number of blades on the power coefficient required further consideration of the blade geometry. According to the research findings, when the axial induction factor was between 0.25 and 0.4, the maximum power coefficient was better.
The results of DAWTs numerical simulation confirmed that the power coefficient of DAWT was higher than that of HAWT. The flow field analysis fully explained the physical mechanism causing the considerable enhancement of DAWT power output. Finally, this study proposed a direction for the aerodynamic design of DAWT to increase power output. With considerations of cost and power coefficients, the DAWT diffuser should have diffuser length-diameter ratio=0.25 and diffuser diameter ratio=1.4, and with consideration of limited space and the power coefficient, the DAWT diffuser should have diffuser length-diameter ratio=0.25–0.5 and diffuser diameter ratio=1.2. When considering only the power coefficient, the DAWT diffuser should have diffuser length-diameter ratio >=1.0 and diffuser diameter ratio=>=1.8. When determining the number of blades of a DAWT rotor, the blade geometry should be simultaneously considered. As a result, when the rotor is operated at the rated tip speed ratio, the axial induction factor is in the range of 0.25–0.4. If the blade has a geometric design with a large chord length distribution and a small pitch angle distribution, the rotor should use a fewer number of blades.

[1] Dörner, H. H., “Design Philosophy,” University of Stuttgart, Germany, 1997. [http://www.ifb.uni-stuttgart.de/~doerner/edesignphil.html. Accessed 3/7/2012]
[2] Weisbrick, A. L., “Feature Review of Some Advanced and Innovative Design Concepts in Wind Energy Conversion Systems,” Miami International Conference on Alternative Energy Sources, Miami Beach, Florida, United States, Dec. 5-7, 1977, pp. 847-859.
[3] Vas, I. E., “A Review of The Current Status of The Wind Energy Innovative System Projects,” Solar Energy Research Institute, United States Department of Energy, SERI/TP-635-469, March 1980.
[4] Sivasegram, S., “Power Augmentation in Wind Rotors: A Review,” Wind Engineering, Vol. 10, No. 3, 1986, pp. 163-179.
[5] Lowe, J. E. and Wiesner, W., “Status of Boeing Wind-turbine Systems,” IEE Proceedings, Vol. 130, Pt. A, No. 9, Dec. 1983, pp.531-536.
[6] Templin, R. J. and Rangi, R. S., “Vertical-axis Wind Turbine Development in Canada,” IEE Proceedings, Vol. 130, Pt. A, No. 9, Dec. 1983, pp. 555-561.
[7] World Wind Energy Report 2010, World Wind Energy Association, Apr. 2011.
[8] Rankine, W. J. M. “On the Mechanical Principles of the Action of Propellers,” Transaction of the Institute of Naval Architects, Vol. 6, 1865, pp. 13-39.
[9] Froude, W., “On the Elementary Relation Between Pitch, Slip and Propulsive Efficiency,” Transaction of the Institute of Naval Architects, Vol. 19, 1878, pp. 47-57.
[10] Froude, R. E., “On the Part Played in Propulsion by Differences of Fluid Pressure,” Transactions of the Institution of Naval Architects, Vol. 30, 1889, pp. 390-405.
[11] Drzewiecki, S., “Bulletin de L’Association Technique Maritime,” Paris. A Second Paper in 1901, 1892.
[12] Lanchester, F. W., “A Contribution to the Theory of Propulsion and the Screw Propeller,” Transactions of the Institution of Naval Architects, Vol. 57, 1915, pp. 98-116.
[13] Betz, A., Introduction to the Theory of Flow Machines, 1st English ed., Oxford, New York, Pergamon Press, 1966.
[14] Joukowsky, N. E., “Windmill of the NEJ Type,” Transactions of the Central Institute for Aero-hydrodynamics of Moscow, 1920.
[15] Glauert, H., “Airplane Propellers,” Aerodynamic Theory, W. F. Durand (ed.), Vol. 4, Division L, Julius Springer, Berlin, 1935, pp169-360.
[16] Wilson, R. E., Lissaman, P. B.S., and Walker, S. N., “Aerodynamic Performance of Wind Turbines,” Corvallis, Oregon, Oregon State University, June 1976.
[17] Betz, A. with Appendix by Prandtl, L., “Schraubenpropeller mit Geringstem Energieverlust,” Vier Abhandlungen Zur Hydrodynamik und Aerodynamik, Göttinger Nachrichten, Göttingen, 1919, pp. 193-217.
[18] Goldstein, S., “On the Vortex Theory of Screw Propellers,” Proceedings of the Royal Society of London. Series A, Vol. 123, No. 792, Apr. 1929, pp. 440-465.
[19] Prandtl, L., “Applications of Modern Hydrodynamics to Aeronautics,” Classical Aerodynamic Theory, R. T. Jones, ed., NASA Reference Publication 1050, 1979.
[20] Lilley, G. M. and Rainbird, W. J., “A Preliminary Report on the Design and Performance of Ducted Windmills,” Cranfield, CoA Report No. 102, 1956.
[21] Wilson, R. E. and Lissaman, P. B. S., “Applied Aerodynamics of Wind Power Machines,” Corvallis, Oregon, Oregon State University, May 1974.
[22] Lewis, R. I., Williams, J. E., and Abdelghaffar, M. A., “A Theory and Experimental Investigation of Ducted Wind Turbines,” Wind Engineering, Vol. 1, No. 2, 1977, pp. 104-125.
[23] de Vries, O., “Fluid Dynamic Aspects of Wind Energy Conversion,” AGARD-AG- 243, 1979.
[24] Riegler, G., “Principles of Energy Extraction from a Free Stream by Means of Wind Turbines,” Wind Engineering, Vol. 7, No. 2, 1983, pp. 115-126.
[25] Dick, E., “Momentum Analysis of Wind Energy Concentrator Systems,” Energy Conversion and Management, Vol. 24, Issue 1, 1984, pp. 19-25.
[26] Dick, E., “Power Limits for Wind Energy Concentrator Systems,” Wind Engineering, Vol. 10, No. 2, 1986, pp. 98-115.
[27] Kogan, A. and Nissim, E., “Shrouded Aerogenerator Design Study I. Two-dimensional Shroud Performance,” Bulletin of the Research Council of Israel, Vol. 11, 1962, pp. 67-88.
[28] Kogan, A. and Seginer, A., “Shrouded Aerogenerator Design StudyⅡ. Axisymmetircal Shroud Performance,” Proceedings of the Fifth Israel Annual Conference on Aviation and Astronautics, Israel, 1963.
[29] Seginer, A., “Flap-Augmented Shrouds for Aerogenerators,” Proceedings of the Second Greater Los Angeles Area Energy Symposium, Los Angeles, Calif., May 19, 1976. Energy LA: Tackling the Crisis. North Hollywood, Calif., Western Periodicals Co., 1976, pp. 188-196.
[30] Igra, O., “Shrouds for Aerogenerator,” 14th American Institute of Aeronautics and Astronautics, Aerospace Sciences Meeting, Washington, D.C., United States, Jan. 26-28, 1976.
[31] Igra, O., “Shrouds for Aerogenerators,” AIAA Journal, Vol.14, No.10, Oct. 1976, pp. 1481-1483.
[32] Igra, O., “Design and Performance of a Turbine Suitable for an Aerogenerator,” Energy Conversion, Vol. 15, 1976, pp. 143-151.
[33] Igra, O., “Compact Shrouds for Wind Turbines,” Energy Conversion, Vol. 16, Issue 4, 1977, pp. 149-157.
[34] Igra, O., “Preliminary results from the shrouded wind-turbine pilot plant,” Journal of Energy, Vol. 4, 1980, pp. 190-192.
[35] Igra, O., “Research and Development for Shrouded Wind Turbines,” Energy Conservation and Management, Vol. 21, 1981, pp. 13-48.
[36] Mitchell, R. L. and Jacobs, E. W., “The SERI Advanced and Innovative Wind Energy Concepts Program,” 1983 Annual Meeting of the American Solar Energy Society, Minneapolis, Minnesota, June 1-3, 1983.
[37] Foreman, K. M., Gilbert, B., and Oman, R. A., “Diffuser Augmentation of Wind Turbines,” Solar Energy, Vol. 20, Issue 4, 1978, pp. 305-311.
[38] Gilbert, B. L., Oman, R. A., and Foreman, K. M., “Fluid Dynamics of Diffuser-Augmented Wind Turbines,” Journal of Energy, Vol. 2 , No. 6, 1978, pp. 368-374.
[39] Gilbert, B. L. and Foreman, K. M., “Experimental Demonstration of the Diffuser-Augmented Wind Turbine Concept,” Journal of Energy, Vol. 3, No. 4, 1979, pp. 235-240.
[40] Foreman, K. M. and Gilbert, B. L., “Further investigations of diffuser augmented wind turbines Part II Technical Report,” U.S. Dept. of Energy Report COO-2616-2 (Pt. 2) (Rev. 2), July 1979.
[41] Foreman, K. M. and Gilbert, B. L., “Technical Development of the Diffuser Augmented Wind Turbine (DAWT) Concept,” Wind Engineering, Vol. 3, No. 3, 1979, pp.153-166.
[42] Gilbert, B. L. and Foreman, K. M., “Experiments with a Diffuser-Augmented Model Wind Turbine,” ASME Journal of Energy Resources Technology, Vol. 105, No. 3, 1983, pp. 46-53.
[43] Loeffler, A. L., Jr., and Vanderbilt, D., “Inviscid Flow Through Wide Angle Diffuser with Actuator Disk,” AIAA Journal, Vol. 16, No. 10, Oct. 1978, pp. 1111-1112.
[44] Loeffler, A. L., Jr., “Flow Field Analysis and Performance of Wind Turbines Employing Slotted Diffusers,” ASME Journal of Solar Energy Engineering, Vol. 103, Issue 1, 1981, pp. 17-22.
[45] Fletcher, C. A. J. and Roberts, B. W., “Electricity Generation from Jet-Stream Winds,” Journal of Energy, Vol. 3, 1979, pp. 241-249.
[46] Fletcher, C. A. J., “Diffuser-Augmented Wind Turbine Analysis,” 7th Australasian Hydraulics and Fluid Mechanics Conference, Brisbane, August 18-22, 1980.
[47] Fletcher, C. A. J., “Computational Analysis of Diffuser-Augmented Wind Turbines,” Energy Conversion and Management, Vol. 21, Issue 3, 1981, pp. 175-183.
[48] van Bussel, G. J. W., “An Assessment of The Performance of Diffuser Augmented Wind Turbines,” Proceedings of the 3th ASME/JSME Joint Fluids Engineering Conference, San Francisco, California, July 18-23, 1999.
[49] Badawy, M. T. S. and Aly, M. E., “Gas Dynamic Analysis of the Performance of Diffuser Augmented Wind Turbine,” Sadhana, Vol. 25, Part 5, Oct. 2000, pp. 453-461.
[50] Lawn, C. J., “Optimization of the Power Output from Ducted Turbines,” Proceedings of the Institution of Mechanical Engineers Part A: Power & Energy, Vol. 217, Issue 1, Feb. 2003, pp. 107-117.
[51] van Bussel, G. J. W., “The Science of Making More Torque from Wind: Diffuser Experiments and Theory Revisited,” Journal of Physics: Conference Series, Vol. 75, 2007.
[52] Werle, M. J. and Presz, W. M., J., “Ducted Wind/Water Turbines and Propellers Revisted,” Journal of Propulsion and Power, Vol. 24, No. 5, 2008, pp. 1146-1150.
[53] Werle, M. J. and Presz, W. M., J., “Shroud and Ejector Augmenters for Subsonic Propulsion and Power Systems,” Journal of Propulsion and Power, Vol. 25, No. 1, 2009, pp. 228-236.
[54] Jamieson, P. M., “Generalized Limits for Energy Extraction in a Linear Constant Velocity Flow Field,” Wind Energy, Vol. 11, Issue 5, 2008, pp. 445-457.
[55] Jamieson, P. M., “Beating Betz: Energy Extraction Limits in a Constrained Flow Field,” Journal of Solar Energy Engineering, Vol. 131, Aug. 2009, pp. 031008-1-031008-6.
[56] Nash, T. A., “Design and Construction of the Vortec 7,” New Zealand Wind Energy Association, 1st Annual Conference, Wellington, June 1997.
[57] Phillips, D. G., Richards, P. J., Mallinson, G. D., and Flay, R. G. J., “Computational Modelling of Diffuser Design for a Diffuser Augmented Wind Turbine,” 13th Australasian Fluid Mechanics Conference, Monash University, Melbourne, Australia, Dec. 13-18, 1998.
[58] Phillips, D. G., Flay, R. G. J., and Nash, T. A., “Aerodynamic Analysis and Monitoring of the Vortec 7 Diffuser-augmented Wind Turbine,” IPENZ Transaction, Vol. 26, 1999, pp. 13-19.
[59] Phillips, D. G., Nash, T. A., Oakey, A., Flay R. G. J., and Richards, P. J., “Computational Fluid Dynamics and Wind Tunnel Modeling of a Diffuser Augmented Wind Turbine,” Wind Engineering, Vol. 23, No. 1, 1999, pp. 7-13.
[60] Phillips, D. G., Richards, P. J., and Flay, R. G. J., “Diffuser Development for a Diffuser Augmented Wind Turbine Using Computational Fluid Dynamics,” Proceedings of the Eighth International PHOENICS Users Conference, 2000.
[61] Phillips, D. G., Richards, P. J., and Flay, R. G. J., “CFD Modeling and the Development of the Diffuser Augmented Wind Turbine,” Wind and Structures, Vol. 5, No. 2, 2002, pp. 267-276.
[62] Schaffarczyk, A. P. and Phillips, D. G., “Design Principles for a Diffuser Augmented Wind-Turbine Blade,” 2001 European Wind Energy Conference and Exhibition, Copenhagen, Denmark, 2001, pp. 488-490.
[63] Phillips, D. G., “An Investigation on Diffuser Augmented Wind Turbine Design,” Ph. D. Thesis, Department of Mechanical Engineering, University of Auckland, Auckland, New Zealand, 2003.
[64] Hansen, M. O. L., Sørensen, N. N., and Flay, R. G. J., “Effect of Placing a Diffuser around a Wind Turbine,” Wind Energy, Vol. 3, 2000, pp. 207-213.
[65] Inoue, M., Sakurai A., and Ohya,Y., “A Design Method of Wind Turbine with Brimmed-Diffuser,” Wind Energy, Vol. 26, No.2, 2002, pp. 71-74.
[66] Abe, K. and Ohya, Y., “An Investigation of Flow Fields Around Flanged Diffusers Using CFD,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 92, 2004, pp. 315-330.
[67] Abe, K., Nishida, M., Sakurai, A., Ohya, Y., Kihara, H., Wada, E., and Sato, K., “Experimental and Numerical Investigations of Flow Fields Behind a Small Wind Turbine with a Flanged Diffuser,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 93, 2005, pp. 951-970.
[68] Abe, K., Kihara, H., Sakurai, A., Wada, E., Sato K., Nishida, M., and Ohya, Y., “An Experimental Study of Tip-vortex Structures Behind a Small Wind Turbine with a Flanged Diffuser,” Wind and Structure, Vol. 9, No. 5, 2006, pp.413-417.
[69] Hasegawa, M., Ohya, Y., and Kume, H., “Numerical Studies of Flows Around a Wind Turbine Equipped with a Flanged Diffuser Shroud Using an Actuator-disc Model,” The 4th International Symposium on Computational Wind Engineering (CWE2006), July 2006.
[70] Ohya, Y., Karasudani, T., Sakurai, A., Abe, K., and Inoue, M., “Development of a Shrouded Wind Turbine with a Flanged Diffuser,” Journal of Wind Engineering and Industrial Aerodynamics, Vol. 96, Issue 5, 2008, pp. 524-539.
[71] Toshimitsu, K., Nishikawa, K., Haruki, W., Oono, S., Takao, M., and Ohya, Y., “PIV Measurements of Flows around the Wind Turbines with a Flanged-Diffuser Shroud,” Journal of Thermal Science, Vol. 17, No. 4, 2008, pp. 375-380.
[72] Ohya, Y. and Karasudani, T., “A Shrouded Wind Turbine Generating High Output Power with Wind-lens Technology,” Energies, Vol. 3, Issue 4, 2010, pp. 634-649.
[73] Ohya, Y., Karasudani, T., Nagai, T., Matsuura, C. T., and Griffiths, H., “Development of Shrouded Wind Turbines with Wind-lens Technology,” EWEA 2011, Brussels, Belgium: Europe’s Premier Wind Energy Event, PO.255_B, 2011.
[74] Anzai, A., Nemoto, Y. and Ushiyama, I., “Wind Tunnel Analysis of Concentrators for Augmented Wind Turbines,” Wind Engineering, Vol. 28, No. 5, 2004, pp. 605-614.
[75] Matsushima, T., Takagi, S., and Muroyama, S., “Characteristics of a Highly Efficient Propeller Type Small Wind Turbine with a Diffuser,” Renewable Energy, Vol. 31, 2006, pp. 1343-1354.
[76] Mertens, S., “Wind Energy in the Built Environment Concentrator Effects of Buildings,” Ph. D. Thesis, Aerospace Engineering, Delft University of Technology, Delft, Nederland, 2006.
[77] P. D. C. ten Hoopen B. Sc., “An Experimental and Computational Investigation of a Diffuser Augmented Wind Turbine: With an application of vortex generators on the diffuser trailing edge,” Master of Science Thesis, Aerospace Engineering, Delft University of Technology, Delft, Nederland, 2009.
[78] Bet, F. and Grassmann, H., “Upgrading Conventional Wind Turbines,” Renewable Energy, Vol. 28, 2003, pp. 71-78.
[79] Grassmann, H., Bet, F., Cabras, G., Ceschia, M., Cobai, D., and DelPapa, C., “A Partially Static Turbine-first Experimental Results,” Renewable Energy, Vol. 28, 2003, pp. 1779-1785.
[80] Grassmann, H., Bet, F., Ceschia, M., and Ganis, M. L., “On the Physics of Partially Static Turbines,” Renewable Energy, Vol. 29, Issue 4, 2004, pp. 491-499.
[81] Badr, E. A. and Ghajar, R. F., “Power Augmentation of Wind Turbines: Experimental study,” European Power and Energy Systems, Marbella, Spain , Sept. 3-5, 2003.
[82] Ghajar, R. F. and Badr, E. A., “An Experimental Study of a Collector and Diffuser System on a Small Demonstration Wind Turbine,” International Journal of Mechanical Engineering Education, Vol. 36, No. 1, 2008, pp. 58-68.
[83] Frankovic´, B. and Vrsalovic´, I., “New High Profitable Wind Turbines,” Renewable Energy, Vol. 24, 2001, pp. 491-499.
[84] Gupta, A., “Prediction of Aerodynamic Forces on Wind Turbine Blades Using Computational Fluid Dynamics,” Master of Applied Science Thesis, Industrial Systems Engineering, University of Regina, Regina, Saskatchewan, Canada, 2007.
[85] Wang, S. H. and Chen, S. H., “Blade Number Effect for a Ducted Wind Turbine,” Journal of Mechanical Science and Technology, Vol. 22, No. 10, 2008, pp. 1984-1992.
[86] Moeller, M. M. and Visser, K. D., “Experimental and Numerical Studies of a High Solidity, Low Tip Speed Ratio DAWT,” AIAA-2010-1585, 48th AIAA Aerospace Sciences Meeting and Exhibit, Orlando, Florida, Jan. 4-7, 2010.
[87] Gaden, D. L. F., “An Investigation of River Kinetic Turbines: Performance enhancements, turbine modeling techniques, and an assessment of turbulence models,” Master of Science Thesis, University of Manitoba, Manitoba, Canada, 2007.
[88] Gaden, D. L. F. and Bibeau, E. L., “A Numerical Investigation into the Effect of Diffusers on the Performance of Hydro Kinetic Turbines Using a Validated Momentum Source Turbine Model,” Renewable Energy, Vol. 35, 2010, pp. 1152-1158.
[89] Shives, M., “Hydrodynamic Modeling, Optimization and Performance Assessment for Ducted and Non-ducted Tidal Turbines,” Master of Applied Science Thesis, Carleton University, Ontario, Canada, 2008.
[90] Shives, M. and Crawford, C., “Overall Efficiency of Ducted Tidal Current Turbines,” IEEE Oceanic Engineering Society Newsletter, Dec. 2010, pp. 20-25.
[91] Shives, M. and Crawford, C., “Ducted Turbine Blade Optimization Using Numerical Simulation,” ISOPE-2011, Maui, Hawaii, USA, June 19-24, 2011.
[92] Shives, M. and Crawford, C., “Developing an Empirical Model for Ducted Tidal Turbine Performance Using Numerical Simulation Results,” Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy, Vol. 226, 2012, pp. 112-125.
[93] Khunthongjan, P. and Teeboonma, U., “Duct Design for Water Current Turbine Application,” GMSARN International Conference on Energy Security and Climate Change: Problems & Issues in GMS, Nov. 25-27, 2009.
[94] Khunthongjan, P., “An Investigation of Diffuser for Water Current Turbine Application Using CFD,” International Journal of Engineering Science and Technology, Vol. 3, No. 4, 2011, pp. 3437-3445.
[95] Khunthongjan, P. and Janyalertadun, A., “A Study of Diffuser Angle Effect on Ducted Water Current Turbine Performance Using CFD,” Songklanakarin Journal of Science and Technology, Vol. 34, No. 1, 2012, pp. 61-67.
[96] Setoguchi, T., Shiomi, N., Kaneko, K., “Development of Two-way Diffuser for Fluid Energy Conversion System,” Renewable Energy, Vol. 29, 2004, pp. 1757-1771.
[97] Münch, C., Vonlanthen, M., Gomes, J., Luquet, R., Guinard, P., and Avellan, F., “Design and Performance Assessment of a Tidal Ducted Turbine,” 3rd IAHR Meeting, Issue: 3, 2009, pp. 571-582.
[98] Reinecke, J., von Backström, T. W., and Venter, G., “Effect of a Diffuser on the Performance of an Ocean Current Turbine,” 9th European Wave and Tidal Energy Conference, Sept. 5-9, 2011.
[99] Scherillo, F., Maisto, U., Troise, G., Coiro, D. P., and Miranda, S., “Numerical and Experimental Analysis of a Shrouded Hydroturbine,” Clean Electrical Power (ICCEP), 2011 International Conference on Date of Conference, June 14-16, 2011, pp. 216-222.
[100] Akhgari, A., “Experimental Investigation of the Performance of a Diffuser Augmented Vertical Axis Wind Turbine,” Master of Applied Science Thesis, University of Tehran, Tehran, Iran, 2007.
[101] Geurts, B. M., Ferreira, C. J. S., and van Bussel, G. J. W., “Aerodynamic Analysis of a Vertical Axis Wind Turbine in a Diffuser,” Torque 2010, The Science of making Torque from Wind, Crete, Greece, June 28-30, 2010.
[102] Nabavi, Y., “Numberical Study of the Duct Shape Effect on the Performance of a Ducted Vertical Axis Tidal Turbine,” Master of Applied Science Thesis, Amirkabir University of Technology, Tehran, Iran, 2004.
[103] Alidadi, M., “Duct Optimization for a Ducted Vertical Axis Hydro Current Turbine, Ph. D. Thesis,” The University of British Columbia, Vancouver, Canada, 2009.
[104] Roa, A. M., Aumelas, V., Maître, T., and Pellone, C., “Numerical and Experimental Analysis of a Darrieus-type Cross Flow Water Turbine in Bare and Shrouded Configurations,” Earth and Environmental Science, Vol. 12, 2010, 012113.
[105] Kirke, B. K., “Tests on Ducted and Bare Helical and Straight Blade Darrieus Hydrokinetic Turbines,” Renewable Energy, Vol. 36, 2011, pp. 3013-3022.
[106] Blanch, M. J., “Wind Energy Technologies for Use in the Built Environment,” Wind Engineering, Vol. 26, No. 3, 2002, pp. 125-143.
[107] Dannecker, R. K. W. and Grant, A. D., “Investigations of a Building-integrated Ducted Wind Turbine Model,” Wind Energy, Vol. 5, 2002, pp. 53-71.
[108] Grant, A., Johnstone, C., and Kelly, N., “Urban Wind Energy Conversion: The potential of ducted turbines,” Renewable Energy, Vol. 33, 2008, pp. 1157-1163.
[109] Aguiló, A., Taylor, D., Quinn, A., and Wiltshire, R., “Computational Fluid Dynamic Modelling of Wind Speed Enhancement Through a Building-augmented Wind Concentration System,” 2004 European Wind Energy Conference and Exhibition, London, UK, Nov. 22-25, 2004.
[110] Beller, C., “Layout Design for a Venturi to Encase a Wind Turbine, Integrated in a High Rise,” 2008 European Wind Energy Conference and Exhibition, Brussels, Belgium, Mar. 31 - Apr. 3, 2008.
[111] Watson, S. J., Infield, D. G., Barton, J. P., and Wylie, S. J., “Modeling of the Performance of a Building-Mounted Ducted Wind Turbine,” Journal of Physics: Conference Series, Vol. 75, 012001, 2007.
[112] Wylie, S. J., Watson, S. J., and Infield, D. G., “Modeling the Output of a Flat-roof Mounted Wind Turbine with an Edge Mounted Lip,” 2008 European Wind Energy Conference and Exhibition, Brussels, Belgium, Mar. 31 - Apr. 3, 2008.
[113] van Beveren, S. C., “Design of an Urban Wind Turbine with Diffuser,” Master of Science Thesis, Aerospace Engineering, Delft University of Technology, Delft, Nederland, 2008.
[114] Reynolds, O., “On the Dynamical Theory of Incompressible Viscous Fluids and the Determination of the Criterion,” Philosophical Transactions of the Royal Society of London, Series A, Vol. 186, 1895, pp. 123-164.
[115] Baliga, B. R. and Patankar, S. V., “A Control Volume Finite-element Method for Two-dimensional Fluid Flow and Heat Transfer,” Numerical Heat Transfer, Vol. 6, 1983, pp. 245-261.
[116] Barth, T. J. and Jesperson, D. C., “The Design and Application of Upwind Schemes on Unstructured Meshes,” AIAA Paper 89-0366, 1989.
[117] Rhie , C. M. and Chow, W. L., “A Numerical Study of the Turbulent Flow Past an Isolated Airfoil with Trailing Edge Separation,” AIAA Paper 82-0998, 1982.
[118] Launder, B. E. and Spalding, D. B., “The Numerical Computation of Turbulent Flows,” Computer Methods in Applied Mechanics and Engineering, Vol. 3, 1974, pp. 269-289.
[119] Menter, F. R., “Two-equation Eddy-viscosity Turbulence Models for Engineering Applications,” AIAA Journal, Vol. 32, No. 8, 1994, pp. 1598-1605.
[120] Wilcox, D. C., “Multiscale Model for Turbulent Flows,” AIAA 24th Aerospace Sciences Meeting American Institute of Aeronautics and Astronautics, 1986.
[121] Johnson, D. A. and King, L. S., “Mathematically Simple Turbulence Closure Model for Attached and Separated Turbulent Boundary Layers,” AIAA Journal, Vol. 23, No. 11, 1985, pp 1684-1692.
[122] Hand, M. M., Simms, D. A., Fingersh, L. J., Jager, D. W., Cotrell, J. R., Schreck, S. J., and Larwood, S. M., “Unsteady Aerodynamics Experiment Phase VI: Wind Tunnel Test Configurations and Available Data Campaigns,” NREL/TP-500-29955, NREL, Golden, CO, 2001.
[123] Simms, D. A., Schreck, S. J., Hand, M. M., and Fingersh, L. J., “NREL Unsteady Aerodynamics Experiment in the NASA-Ames Wind Tunnel: A Comparison of Predictions to Measurements,” NREL/TP-500-29494, NREL, Golden, CO, 2001.
[124] Giguere, P. and Selig, M. S., “Design of a Tapered and Twisted Blade for the NREL Combined Experiment Rotor,” NREL/SR-500-26173, NREL, Golden, CO, 1999.
[125] Sørensen, N. N., Michelsen, J. A., and Schreck, S., “Navier-Stokes Predictions of the NREL Phase VI rotor in the NASA Ames 80 ft × 120 ft Wind Tunnel,” Wind Energy, Vol. 5, 2002, pp.151-169.
[126] Himmelskamp, H., “Profiluntersuchungen an einem umlaufenden Propeller,” Dissertation, Göttingen 1945; Mitt. Max-Planck-Institut für Strömungsforschung Göttingen Nr. 2, 1950.