Statkraft Ocean Energy

Research Program

Design of a reference tidal turbine

Blade design with the blade element

momentum theory (BEM) - Iterative approach applying the BEM to optimize the chord

length and twist angle of each section

- Importation of the sections from BEM to Pro-engineer®

software for a 3D drawing

- Creation of the close surrounding around the blade: the blade

is cut out from half a disc

- Exportation to ANSYS® for CFD computations

CFD verification ► Objectives: to check the design in term of efficiency and

cavitation

►Tool: ANSYS® CFX software running with Reynolds-averaged

Navier–Stokes (RANS) equations

► Method:

- Current at design velocity only (2,5 m/s, without wave)

- Calculated rotational velocity (15,9 rpm)

- One blade is studied, but the whole rotation is considered by

using “rotational periodicity” at the base interface

Reference tidal turbine

Tests in MARINTEK’s towing tank -Trondheim ► Objectives: to create a unique experimental database for

validation of numerical approaches for horizontal-axis tidal turbines

located at wave exposed tidal turbine sites

► Equipment: A 1/14 scaled rotor is fixed on a carriage structure

moving along the tank to symbolize the current. Different carriage

speeds will represent different current velocity. The towing tank is

equipped with a wave maker able to generate regular and irregular

waves.

► Results:

- From the pressure distribution it

is possible to get:

The efficiency

The cavitation number

-The prototype blade has an

efficiency of 42% whereas the

small scaled model is extracting

35% of the flow energy

- This study points out scale

effects, which has to be

considered when analyzing the

model test results

Tidal turbine main properties -Power output 1MW

- 2 blades

- Rotor diameter: 21 m

- Constant Tip Speed Ratio 7

- Variable speed control

- Design current velocity 2,5m/s

- Turbine speed 15,9 rpm

- Water depth to still sea level 36 m

- Rotor axis depth 18,5 m

- Profiles: S816, S825 and S826

Future work ► To introduce waves in CFD calculations

► To predict the scale effect on the blade

► To analyze the tests result and deal with fatigue phenomenon

The tests will include: - efficiency tests with TSR from 3 to 9

- measurements with rotor subjected to current and regular

waves by combining:

- 4 different carriage velocities from 0 m/s to 1,07 m/s

- 3 wave steepnesses from 1/30 to 1/10

- 3 wave periods from 1,34s to 2,67s

Sensors will measure:

- Rotor position in the tank

- Blades angular position

- Wave crest position

- Torque

- Forces along the blades

Project issue - To create an open documentation describing design

methods, experiments and results to constitute a database for

teaching and research purposes.

- To reduce the risk of blade and turbine failure at wave

exposed tidal turbine sites by finding the dimensioning

dynamical loads

Wave-current interaction Fatigue loads Dynamical loads on the blades come from:

- the tides: changes in current velocity and direction

- the waves: cyclic water particle velocity with an amplitude

- the combination vertical velocity profile + rotation

- the turbulence, described with a spectrum

Blade and close surrounding drawn

with Pro-engineer

Vertical current velocity profile

(power law, in blue) summed

with water particle velocity due

to waves (in red and green)

Pressure distribution on the suction

and pressure side respectively

Celine Faudot, PhD Candidate, Energy and Process Engineering, NTNU

Supervised by Ole Gunnar Dahlhaug