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Radiused Edge Blade Tip for a Wider Operating Range in Wells Turbine

  • Research Article-Mechanical Engineering
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Abstract

The narrow operating range of a Wells turbine restricts its energy extraction capability from the ocean waves. In this work, the concept of a radiused edge tip blade (RETB) was introduced to overcome such an issue. The RET modifies the tip and changes the tip leakage flow behaviour. The flow through the turbine annulus was simulated numerically and compared with the existing experimental results of the reference turbine. Three-dimensional Reynolds-averaged Navier–Stokes equations with a two-equation turbulence closure model available in ANSYS CFX 14.5 was used for the simulations. The computational domain was discretized with unstructured tetrahedral elements, and the grid independence study gave an optimal grid. The RETB altered the tip leakage flow characteristics and delayed the stall inception. The RETB enhanced the relative operating range by 25% and peak torque by 37%.

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Abbreviations

C :

Chord length (mm)

Cp:

Pressure coefficient (–)

e 21a , e 32a :

Approximate relative error

\( e_{\text{ext}}^{21} \), \( e_{\text{ext}}^{32} \) :

Extrapolated relative error

\( H = \frac{{R_{\text{hub}} }}{{R_{\text{tip}} }} \) :

Hub to tip ratio (–)

I :

Turbulence intensity (–)

k :

Turbulence kinetic energy (m2/s2)

p :

Pressure (Pa)

Q :

Volume flow rate (m3/s)

y + :

Non-dimensional wall distance (–)

U T :

Peripheral blade velocity (m/s)

V 1 :

Absolute inlet velocity (m/s)

W 1 :

Relative inlet velocity (m/s)

Z :

Number of blades (–)

α :

Angle of attack (°)

ν:

Kinematic viscosity (m2/s)

\( \phi_{\text{ext}}^{12} \), \( \phi_{\text{ext}}^{32} \) :

Extrapolated values

∈:

Turbulence dissipation rate (m2/s3)

\( \eta = \frac{T\omega }{{Q\Delta p_{o} }} \) :

Efficiency (–)

ρ :

Density (kg/m3)

\( \sigma = \frac{Zc}{{2\pi R_{\text{mid}} }} \) :

Solidity (–)

ω :

Angular velocity (rad/s)

LE:

Leading edge

OWC:

Oscillating water column

PS:

Pressure side

RANS:

Reynolds-averaged Navier–Stokes

RET:

Radiused edge tip

RETB:

Radiused edge tip blade

SET:

Sharp edge tip blade

SS:

Suction side

SST:

Shear stress transport

TE:

Trailing edge

TKE:

Turbulence kinetic energy (m2/s2)

WECS:

Wave energy conversion system

r :

Grid refinement factor

R hub :

Blade hub radius (mm)

\( R_{\text{mid}} = \frac{{\left( {R_{\text{tip}} + R_{\text{hub}} } \right)}}{2} \) :

Radius of blade midspan (mm)

R tip :

Blade tip radius (mm)

T :

Torque (N m)

\( T^{*} = \frac{T}{{\rho \omega^{2} R_{\text{tip}}^{5} }} \) :

Torque coefficient (–)

\( U^{*} = \frac{{U_{A} }}{{U_{\text{tip}} }} \) :

Flow coefficient (–)

U A :

Inlet axial velocity (m/s)

U tip :

Blade tip velocity (m/s)

V :

Absolute velocity (m/s)

w :

Specific dissipation rate (s−1)

w bl :

Blade specific work (m2/s2)

W :

Relative velocity (m/s)

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Acknowledgements

The high-speed computing facility provided by the Indian Institute of Technology Madras was gratefully acknowledged.

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Authors and Affiliations

  1. Wave Energy and Fluids Engineering Lab, Ocean Engineering Department, IIT Madras, Chennai, 600036, India

    P. Madhan Kumar & Abdus Samad

  2. Institute of Ocean Energy, Saga University, 1-Honjo-machi, Saga-shi, Saga, 840-8502, Japan

    Paresh Halder

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  1. P. Madhan Kumar
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Correspondence to Abdus Samad.

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Kumar, P.M., Halder, P. & Samad, A. Radiused Edge Blade Tip for a Wider Operating Range in Wells Turbine. Arab J Sci Eng 46, 2663–2676 (2021). https://doi.org/10.1007/s13369-020-05185-z

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