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Flow control by leading edge prism cylinders for a wave energy harvesting turbine

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Abstract

Separated flow on a Wells turbine blade causes poor performance of the turbine. Implementing passive flow control techniques, such as leading-edge prism cylinders (LE-PCs), effectively delays flow separation within a system. The prism cylinder alters the angle of attack (AoA) and modifies the boundary layer profile. The shapes of the prism cylinders were square, hexagonal, octagonal, and decagonal. The prism cylinder circumference was fixed at 2% of the chord length (C), and the gap between the PC and the LE was 2.5%C and 3.5%C. The prism cylinder was placed at the blade chord line to maintain the Wells turbine symmetry. For the numerical simulations, the turbine performance parameters are calculated using steady-state Reynolds-averaged Navier–Stokes (RANS) equations along with a k–ω SST turbulence model. Results showed that a gap of 3.5%C of the hexagonal prism cylinder improves the performance and provides a more comprehensive working range of 22.22% and an average torque coefficient of 43%. The prism cylinder modifies vortex strength and kinetic energy of the incoming flow and, finally, manipulates the suction-surface (SS) flow separation and re-energizes the separated flow.

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Abbreviations

CFD:

Computational fluid dynamics

LE:

Leading-edge

NACA:

National Advisory Committee of Aeronautics

OWC:

Oscillating water column

PC:

Prism cylinder

PCAWT:

Prism cylinder assisted Wells turbine

PS:

Pressure side

PTO:

Power take-off device

RANS:

Reynolds-averaged Navier–Stokes

SS:

Suction surface

SST:

Shear stress transport

TKE:

Turbulent kinetic energy (m2/s2)

TLF:

Tip leakage flow

TLV:

Tip leakage vortex

WEC:

Wave energy converter

C :

Chord length (m)

C p :

Static pressure drop coefficient (–)

h = \(\frac{{R}_{{\text{hub}}}}{{R}_{{\text{tip}}}}\) :

Hub-to-tip ratio (–)

K :

Specific turbulent kinetic energy (m2/s2)

Q :

Airflow rate (m3/s)

R hub :

Hub radius (m)

R tip :

Tip radius (m)

T t :

Total torque (N m)

U A :

Inlet axial velocity (m/s)

U tip :

Rotor tip velocity (m/s)

ε :

Dissipation rate (m2/s3)

Ρ :

The density of air (kg/m3)

Ω :

Rotational speed (rpm)

ω :

Specific turbulent dissipation rate (s−1)

Δp :

Stagnation pressure drop (Pa)

T* =\(\frac{{T}_{t}}{\rho {\Omega }^{2}{D}_{{\text{tip}}}^{5}}\) :

Torque coefficient (–)

\(U*\hspace{0.17em}=\frac{{U}_{A}}{{U}_{{\text{tip}}}}\) :

Flow coefficient (–)

Δp * = \(\frac{\Delta p}{\rho {\Omega }^{2}{D}_{{\text{tip}}}^{2}}\) :

Pressure loss coefficient (–)

\(\eta =\frac{{T}_{t}\Omega }{Q\Delta p}\) :

Efficiency (%)

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Acknowledgements

The authors are grateful to the Indian Institute of Technology Madras (IIT Madras) in Chennai, Tamil Nadu, for providing the facilities and support that made this research possible.

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Authors and Affiliations

  1. Wave Energy and Fluids Engineering Laboratory, Indian Institute of Technology Madras, Chennai, India

    P. Sadees & Abdus Samad

Authors
  1. P. Sadees
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  2. Abdus Samad
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Contributions

PS conceptualization, methodology, software usage, validation, formal analysis, investigation, data curation, writing—original draft, visualization. AS resources, writing—review and editing, supervision.

Corresponding author

Correspondence to Abdus Samad.

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Sadees, P., Samad, A. Flow control by leading edge prism cylinders for a wave energy harvesting turbine. J. Ocean Eng. Mar. Energy (2024). https://doi.org/10.1007/s40722-024-00317-1

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  • DOI: https://doi.org/10.1007/s40722-024-00317-1

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