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Performance Improvement in a Helical Savonius Wind Rotor

  • Research Article-Mechanical Engineering
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Abstract

Above all vertical axis wind turbines, for their lower cost and independent on wind direction, Savonius rotor takes the advantage to be more suitable for some implementation. Thus, many investigations have been carried out to improve its efficiency. This study emphasizes on the effect of the overlap distance and the blade shape on a helical Savonius wind turbine performance. Assessment methods based on the flow field characterizations, the variation of torque and power coefficient are performed. Thus, transient simulations using the SST k–ω turbulence model are carried out. The numerical model is validated using wind tunnel tests. Results indicate that the non-overlapped helical Savonius rotor highlights higher maximum power coefficient of 0.124 at a tip speed ratio of 0.73 over rotors with overlap distance of 10 mm, 15 mm and 20 mm, respectively. In addition, the delta-bladed rotor improves the performance of the helical Savonius rotor by 14.51%. With the novel blade shape, the maximum power coefficient reaches a value of 0.142 at a tip speed ratio of 0.78. The obtained results present an interesting data that could provide the aerodynamic characteristics of the airflow for the designers and engineers to enhance the efficiency of the helical Savonius turbine.

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Abbreviations

A :

Projected area (m2)

A r :

Aspect ratio, dimensionless

C Ts :

Static torque coefficient, dimensionless

C p :

Power coefficient, dimensionless

C T :

Torque coefficient, dimensionless

C p max :

Maximum power coefficient, dimensionless

C T max :

Maximum torque coefficient, dimensionless

C pr :

Pressure coefficient, dimensionless

D :

Rotor diameter (m)

D e :

End plate diameter (m)

d :

Blade chord length (m)

e :

Overlap distance (m)

F i :

External applied forces (N)

G k :

Production term of turbulence (kg m−1 s−3)

H :

Rotor height (m)

k :

Turbulent kinetic energy (m2 s−2)

O r :

Overlap ratio, dimensionless

p :

Pressure (Pa)

P :

Blade shape common portion (m)

P f :

Static pressure on blades surface (Pa)

P r :

Mechanical power (W)

P ref :

Reference pressure (Pa)

P w :

Wind power (W)

R :

Rotor radius (m)

Re:

Reynolds number, dimensionless

s :

Rotor shaft diameter (m)

t :

Time (s)

T d :

Dynamic torque (N m)

T s :

Static torque (N m)

u i :

The velocity component defined in xi = (x, y, z) coordinate direction

u t :

The friction velocity (m s−1)

\( u_{i}^{'} \) :

Fluctuating velocity components (m s−1)

\( \overline{{u^{'}_{i} u^{'}_{j} }} \) :

Reynolds stress tensor components (m2 s−2)

U ∞ :

Wind velocity (m s−1)

V :

Velocity of the flow around the rotor (m s−1)

x :

Cartesian coordinate (m)

t :

Cartesian coordinate (m)

y :

Cartesian coordinate (m)

y n :

Distance of the first node from wall (m)

y + :

Non-dimensional parameter

z :

Cartesian coordinate (m)

β * :

Constant of k–ω turbulent model

β 2 :

Constant of k–ω turbulent model

\( \sigma_{k} \) :

Constant of k–ω turbulent model

\( \sigma_{{_{\omega ,1} }} \) :

Constant of k–ω turbulent model

\( \sigma_{{_{\omega ,2} }} \) :

Constant of k–ω turbulent model

\( \theta \) :

Rotor angular position (rad)

μ :

Dynamic viscosity (Pa s)

μ t :

Turbulent viscosity (Pa s)

ρ :

Air density (kg m−3)

Ω:

Rotating speed (rad s−1)

λ :

Tip sped ratio, dimensionless

ψ :

Twist angle (°)

\( \delta_{ij} \) :

Chronecker indices

γ 2 :

Constant of k–ω turbulent model

Δt :

Time step (s)

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Acknowledgements

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

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Authors and Affiliations

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

    Mariem Lajnef, Mabrouk Mosbahi & Zied Driss

  2. Higher Institute for Technological Studies of Sidi Bouzid, Sidi Bouzid, Tunisia

    Youssef Chouaibi

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  1. Mariem Lajnef
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  2. Mabrouk Mosbahi
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  3. Youssef Chouaibi
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  4. Zied Driss
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Correspondence to Mariem Lajnef.

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Lajnef, M., Mosbahi, M., Chouaibi, Y. et al. Performance Improvement in a Helical Savonius Wind Rotor. Arab J Sci Eng 45, 9305–9323 (2020). https://doi.org/10.1007/s13369-020-04770-6

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  • DOI: https://doi.org/10.1007/s13369-020-04770-6

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