Renewable energy inspired reseach.

1. Performance Studies on a Direct Drive
Turbine for Wave Power Generation in
a Numerical Wave Tank
Professor Young-Ho LEE
Division of Mechanical & Energy System
Engineering,
College of Engineering,
Korea Maritime University, South Korea.
Deepak Prasad
Discipline of Mechanical Engineering,
University of the South Pacific, Fiji Islands.
Dr. M. R. Ahmed
Discipline of Mechanical Engineering,
University of the South Pacific, Fiji Islands.

2. Renewable Energy Sources
2
Wind Power Solar Power Biomass Hydro Power Ocean Energy
Thermal
Energy
Mechanica
l Energy
WaveTide
Fig. 1 Renewable energy sources

3. 3
Introduction
 Wave energy:
 Power flux – 15 to 20 times more than wind and solar.
 Estimated wave energy is in order of 1 to 10 TW.
 Most consistent of all the intermittent sources and truly
renewable.
 Wave tanks have been used over the years to provide:
 helpful information on wave characteristics and
employed to conduct prototype testing. However it is:
 Expensive, time consuming.
 Due to time constraint all design variables can not be tested.

4. 4
Introduction
 To overcome these problems much effort has been
focused on the development of Numerical Wave Tank
(NWT).
 NWT allows for rapid design changes and
improvements in short time.
 With improving computer capabilities it is possible for
these CFD packages to solve and give accurate
solutions of real life problems.

5. 5
Introduction
 The current study employs a 3D NWT based on
Reynolds Averaged Navier-Stokes Equation (RANSE)
to generate waves using commercial CFD code
ANSYS-CFX.
 A cross flow turbine is employed to generate power
from incoming waves.
 Aim:
 To simulate waves using a Numerical Wave Tank.
 To validate the CFD code with the experimental data.
 To study flow characteristics.

6. 6
Base Model
All Dimensions in mm
Fig. 2 Schematic of the entire model
Fig. 3 Schematic of the turbine and runner blade
Parameter Value
Blade entry angle, α 30º
Blade exit angle, β 90º
Outer Diameter, Do 260 mm
Inner Diameter, Di 165 mm
Number of Blades 30
Table 1 Turbine and runner parameters

7.  Full model calculation.
 Numerical Wave Tank (NWT).
 Front Guide Nozzle.
 Augmentation Channel.
 Front Nozzle.
 Rear Nozzle.
 Turbine.
 Rear Chamber.
7
Test Section
Fig. 4 Schematic of the test section

8. CFX-Pre
Computational Domain
8
Simulation Type Transient Wave Maker Piston-Type (Specified Motion)
Turbulence Model k-Epsilon Opening 1 atm
Phase Water & Air @ 25°C Walls No-Slip Condition
Surf. Tension
Coeff.
0.075 N/m Density (kg/m3
) Water = 997, Air 1.18
Opening
Moving mesh section
Wall Motion: Asin(ωt)
Fig. 5 Computational domain.
NWT
Front Guide
Nozzle
Augmentation channel
Rear chamber
Table 2 ANSYS CFX-Pre conditions

9. 9
Wave Height & Velocity (NWT)
Point
Fig. 6 Water wave height in the numerical wave tank
Fig. 8 Velocity contour in the numerical wave tank
Fig. 7 Volume fraction showing the formation of
waves in the wave tank

10. 10
Front Guide Nozzle
Fig. 9 Velocity vector in front guide nozzle
 There is a recirculation region
observed near the top left
corner, denoted by A when
water is flowing in.
 Due to this, the flow was
directed towards the bottom
and hence higher velocity
recorded in region B.
 When water was retreating,
higher velocity was observed
in region A.

11. 11
Front Guide Nozzle
Fig. 10 Average velocity in the front guide nozzle
at different rpm
 It is observed that the velocity
increases as the rpm increases,
reaches a maximum and then
decreases.
 This peak at 35 rpm is due to
better flow characteristic because
of small re-circulating region in the
front guide nozzle.
 This also leads to better flow in the
augmentation channel.

12. 12
Turbine Power
Fig. 11 Comparison between experimental data and CFD results
Variable Unit Experiment CFD
H m 0.2 0.195
T s 2.0 2.0
ΔH m 0.071 0.065
Q m3
/s 0.03 0.032
PWave W/m 86.74 82.46
PWP W 20.85 20.36
Table 3 Comparing experimental and CFD results
 For CFD, the peak power is 6.71 W compared to 6.8 W obtained experimentally.
 The efficiency at 35 rpm is 44.73% and 45.33% respectively from CFD and experiments.
 The difference is within 3%.

13. 13
Flow Characteristics
Fig. 12 Velocity vector in the augmentation channel at 35 rpm
 The flow accelerates approaching
stage 1 as expected. (Nozzle effect)
 The water passes through the turbine
passage at stage 1 while imparting
energy to the runner.
 From the exit at stage 1 to the entry of
blades at stage 2, the flow again
accelerates a little.
 At stage 2, the passing water imparts
energy to the runner once more before
flowing into the rear nozzle.

14. Flow Characteristics
14

15. 15
Conclusion
 Commercial CFD code ANSYS-CFX was successfully
used to generate waves in a NWT using a piston
type wave-maker.
 The results of CFD simulation showed good
agreement with the experimental data. The difference
in result was within 3%.
 The maximum turbine power was obtained at 35 rpm.
For CFD, the maximum power was 6.71 W compared
to 6.8 W obtained experimentally.
 The efficiency at 35 rpm was 44.73% and 45.33%
respectively for CFD and experiment.