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Research Papers: Alternative Energy Sources

Examining the Aerodynamic Drag and Lift Characteristics of a Newly Developed Elliptical-Bladed Savonius Rotor

[+] Author and Article Information
Nur Alom

Department of Mechanical Engineering,
National Institute of Technology Meghalaya,
Shillong 793003, Meghalaya, India
e-mail: nuralomme19@gmail.com

Ujjwal K. Saha

Professor
Department of Mechanical Engineering,
Indian Institute of Technology Guwahati,
Guwahati 781039, India
e-mail: saha@iitg.ernet.in

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received April 15, 2018; final manuscript received September 30, 2018; published online January 9, 2019. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 141(5), 051201 (Jan 09, 2019) (12 pages) Paper No: JERT-18-1273; doi: 10.1115/1.4041735 History: Received April 15, 2018; Revised September 30, 2018

The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.

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Figures

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Fig. 5

Grid independence test: (a) 2D grids and (b) 3D grids

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Fig. 4

Mesh generation around the rotor: (a) 2D mesh and (b) 3D mesh

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Fig. 3

Sectional cut angle of the ellipse

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Fig. 8

Validation of present 2D CD with the available results

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Fig. 9

Validation of present 2D CL with the available results

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Fig. 10

Validation of present 3D results with the available results

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Fig. 11

Validation of numerical (2D) CT with tested results

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Fig. 2

Illustration of lift force, drag force, and relative wind speed

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Fig. 1

Geometric details of Savonius rotor

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Fig. 6

Time independence test

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Fig. 7

Computational domain and boundary conditions

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Fig. 23

Total pressure (N/m2) contours of elliptical- and semicircular-bladed rotors at TSR = 0.6: (a) angle of attack = 90 deg and (b) angle of attack = 150 deg

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Fig. 24

Turbulence intensity (%) contours of elliptical- and semicircular-bladed rotors at TSR = 0.6

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Fig. 17

Total pressure (N/m2) contours of elliptical and semicircular profiles at TSR = 0.6: (a) angle of attack = 90 deg and (b) angle of attack = 50 deg

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Fig. 18:

Turbulence intensity (%) contours of elliptical and semicircular profiles at TSR = 0.6

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Fig. 19

Variation of the 3D CD and CL for the elliptical- and semicircular-bladed rotors at TSR = 0.6

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Fig. 20

Comparison of CD and CL of semicircular profile (2D) and semicircular bladed rotor (3D) at TSR = 0.6

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Fig. 21

Comparison of CD and CL of elliptical profile (2D) and elliptical-bladed rotor (3D) at TSR = 0.6

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Fig. 22

Velocity magnitude (m/s) contours of elliptical- and semicircular-bladed rotors at TSR = 0.6: (a) angle of attack = 90 deg and (b) angle of attack = 150 deg

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Fig. 12

Validation of numerical (2D) CP with tested results

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Fig. 13

Comparison of CT for 2D elliptical and semicircular profiles at TSR = 0.6

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Fig. 14

Variation of CD and CL for the elliptical and semicircular profiles at TSR = 0.6

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Fig. 15

Two-dimensional unsteady variation of CT and CP with TSR of the tested rotors

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Fig. 16

Velocity magnitude (m/s) contours of elliptical and semicircular profiles at TSR = 0.6: (a) angle of attack = 90 deg and (b) angle of attack = 150 deg

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Fig. 25

Schematic diagram of a wind tunnel

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Fig. 26

Tested Savonius rotors: (a) elliptical-bladed rotor and (b) semicircular-bladed rotor

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Fig. 27

Variation of CT and CP with TSR of the tested rotors

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Fig. 28

Blockage corrected CT and CP with TSR of the tested rotors

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