dynamic behaviour of the patented kobold tidal current turbine.pdf

8
Notation Symbol Unit Description a Interference factor c m Blade chord length C d Airfoil drag coefficient C l Airfoil lift coefficient C mc/4 Airfoil quarter chord pitching moment coefficient C D Blade drag coefficient C L Blade lift coefficient C p Turbine performance coefficient C q Turbine torque coefficient D N Drag dF N Elementary force acting on the elemen- tary actuator disk I p kgm 2 Blade moment of inertia I T kgm 2 Turbine moment of inertia L N Lift M Nm Instantaneous turbine torque MC Nm Instantaneous load torque M c/4 Nm Quarter chord pitching moment M m Nm Average turbine torque N N Blade radial force N b Number of blades P W Instantaneous turbine mechanical power P m W Average turbine mechanical power R m Turbine radius Re Blade Reynolds number S m 2 Turbine frontal area T Nm Blade tangential force V m/s Local velocity V R m/s Tip speed V ¥ m/s Asymptotic velocity x c/4 %blade chord Blade aerodynamic centre position x hinge %blade chord Floating hinge position a rad Blade angle of attack a tan rad Angle between the local velocity and the local tangent at the blade a zv rad Blade pitch angle && a rad/s 2 Blade pitch angle acceleration l Tip speed ratio = WR/V ¥ r kg/m 3 Fluid density s Solidity = N b c /R q rad Blade azimuth angle && q rad/s 2 Turbine acceleration W rad/s Turbine angular velocity Subscript d Conditions at the downwind actuator disk u Conditions at the upwind actuator disk h Hinge 1 Introduction Marine current energy is a type of renewable energy resource that has been less exploited than wind energy. Only recent years, have some countries devoted funds to research aimed at developing tidal current power stations. Tidal cur- rent turbines, as in the wind community, can be divided into vertical-axis and horizontal axis types. Although horizontal axis turbines have been more widely used than vertical axis types for wind energy exploitation, vertical axis turbines could present significant advantages for tidal current ex- ploitation, because they are simple to build and reliable in working conditions. Therefore, at beginning of the studies © Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 77 Czech Technical University in Prague Acta Polytechnica Vol. 45 No. 3/2005 Dynamic Behaviour of the Patented Kobold Tidal Current Turbine: Numerical and Experimental Aspects D. P. Coiro, A. De Marco, F. Nicolosi, S. Melone, F. Montella This paper provides a summary of the work done at DPA on numerical and experimental investigations of a novel patented vertical axis and variable pitching blades hydro turbine designed to harness energy from marine tidal currents. Ponte di Archimede S.p.A. Company, located in Messina, Italy, owns the patented KOBOLD turbine that is moored in the Messina Strait, between the mainland and Sicily. The turbine has a rotor with a diameter of 6 meters, three vertical blades of 5 meters span with a 0.4 m chord ad hoc designed curved airfoil, producing high lift with no cavitation. The rated power is 160 kW with 3.5 m/s current speed, which means 25% global system efficiency. The VAWT and VAWT_DYN computer codes, based on Double Multiple Steamtube, have been developed to predict the steady and dynamic performances of a cycloturbine with fixed or self-acting variable pitch straight-blades. A theoretical analysis and a numerical prediction of the turbine performances as well as experimental test results on both a model and the real scale turbine will be presented and discussed. Keywords: vertical-axis-hydro-turbine, variable pitch, Double-Multiple-Streamtube, tidal currents, tidal energy.

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Page 1: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

NotationSymbol Unit Description

a Interference factorc m Blade chord lengthCd Airfoil drag coefficientCl Airfoil lift coefficientCmc/4 Airfoil quarter chord pitching moment

coefficientCD Blade drag coefficientCL Blade lift coefficientCp Turbine performance coefficientCq Turbine torque coefficientD N DragdF N Elementary force acting on the elemen-

tary actuator diskIp kgm2 Blade moment of inertiaIT kgm2 Turbine moment of inertiaL N LiftM Nm Instantaneous turbine torqueMC Nm Instantaneous load torqueMc/4 Nm Quarter chord pitching momentMm Nm Average turbine torqueN N Blade radial forceNb Number of bladesP W Instantaneous turbine mechanical powerPm W Average turbine mechanical powerR m Turbine radiusRe Blade Reynolds numberS m2 Turbine frontal areaT Nm Blade tangential forceV m/s Local velocityVR m/s Tip speed

V�

m/s Asymptotic velocityxc/4 %blade

chordBlade aerodynamic centre position

xhinge %bladechord

Floating hinge position

� rad Blade angle of attack�tan rad Angle between the local velocity and the

local tangent at the blade�zv rad Blade pitch angle��� rad/s2 Blade pitch angle acceleration� Tip speed ratio � �R/V�

� kg/m3 Fluid density� Solidity � Nb c /R� rad Blade azimuth angle��� rad/s2 Turbine acceleration� rad/s Turbine angular velocity

Subscriptd Conditions at the downwind actuator

disku Conditions at the upwind actuator diskh Hinge

1 IntroductionMarine current energy is a type of renewable energy

resource that has been less exploited than wind energy. Onlyrecent years, have some countries devoted funds to researchaimed at developing tidal current power stations. Tidal cur-rent turbines, as in the wind community, can be divided intovertical-axis and horizontal axis types. Although horizontalaxis turbines have been more widely used than vertical axistypes for wind energy exploitation, vertical axis turbinescould present significant advantages for tidal current ex-ploitation, because they are simple to build and reliable inworking conditions. Therefore, at beginning of the studies

© Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 77

Czech Technical University in Prague Acta Polytechnica Vol. 45 No. 3/2005

Dynamic Behaviour of the PatentedKobold Tidal Current Turbine:

Numerical and Experimental AspectsD. P. Coiro, A. De Marco, F. Nicolosi, S. Melone, F. Montella

This paper provides a summary of the work done at DPA on numerical and experimental investigations of a novel patented vertical axis andvariable pitching blades hydro turbine designed to harness energy from marine tidal currents. Ponte di Archimede S.p.A. Company, locatedin Messina, Italy, owns the patented KOBOLD turbine that is moored in the Messina Strait, between the mainland and Sicily. The turbinehas a rotor with a diameter of 6 meters, three vertical blades of 5 meters span with a 0.4 m chord ad hoc designed curved airfoil, producinghigh lift with no cavitation. The rated power is 160 kW with 3.5 m/s current speed, which means 25% global system efficiency. The VAWTand VAWT_DYN computer codes, based on Double Multiple Steamtube, have been developed to predict the steady and dynamicperformances of a cycloturbine with fixed or self-acting variable pitch straight-blades. A theoretical analysis and a numerical prediction ofthe turbine performances as well as experimental test results on both a model and the real scale turbine will be presented and discussed.

Keywords: vertical-axis-hydro-turbine, variable pitch, Double-Multiple-Streamtube, tidal currents, tidal energy.

Page 2: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

vertical axis wind turbines were taken as models for hy-dro-turbines. The blades of Darrieus-type vertical axis windturbines are fixed, and they perform well when the blade so-lidity is low and the working speed is high. For this reason, thefirst hydro-turbines were impossible to start. A variable-pitchblade system can be a solution to this problem. Some proto-types with different variants of this system have thereforebeen developed around the world: the Kobold turbine in theStrait of Messina, Italy; the cycloidal turbine in Guanshan,China; the moment-control turbine at Edinburgh University,UK; and the mass-stabilised system turbine by Kirke andLazauskas in Inman Valley, South Australia. The Kobold tur-bine has been under development since 1997: the rotor has aself-acting variable pitch and the Kobold blades have an ad hocdesigned airfoil, called HLIFT, to be cavitation free andto have high lift performance. The methods for calculat-ing the hydrodynamic performances of vertical axis turbinesalso come from wind turbines: in the 1970s Templin devel-oped the Single-Disk Single-Tube model, and then Stricklandput forward the Single-Disk Multi-Tube model. In the 1980sParaschivoiu introduced the Double-Disk Multi-Tube model.The VAWT and VAWT_DYN computer codes, based on thistheory, have been developed to predict the steady and dy-namic performances of a cycloturbine with fixed or self-actingvariable pitch straight-blades. The numerical results havebeen compared with two sets of experimental data: one set isobtained from wind tunnel tests on a scaled model, and theother set is based on field data from the Kobold prototype.

2 Double multiple streamtubeIn order to analyze the flow field around a vertical axis

turbine, a DMS model was used. The DMS model is an evolu-tion of the previous “momentum models”: the single streamtubemodel, the multiple streamtube model and the doublestreamtube model [1]. The DMS model [2] assumes thatthe flow through the rotor can be modelled by examining theflow through several streamtubes, and the flow disturbance,produced by the rotor is determined by equating the aerody-namic forces on the turbine rotor to the time rate of change inmomentum through the rotor as depicted in Fig. 1. In theDMS model, the flow velocities vary in both the upwind anddownwind regions of the streamtube, as well as varying fromstreamtube to streamtube. So DMS is able to analyse the inter-ference between the downwind blade and the upwind blade’s

wake in order to evaluate more accurately the local value ofthe velocity and the instantaneous blade load. As shownin Fig. 1., the rotor is modelled as a series of elementarystreamtubes, and each streamtube is modelled with two actua-tor disks in series. Across the actuator disk the pressure dropsand this drop is equivalent to the streamwise force dF on theactuator disk divided by the actuator disk area dA.

The elementary force dFu and dFd, respectively on the up-wind and downwind disk, given by the momentum principle,are

d du u uF V A V V� ��� ( )2 (1)

d dd d dF V A V V� �� ( )2 3 (2)

where Vd, which is the velocity on the downwind actuatordisk, is influenced by the velocity Vu on the upwind actuatordisk. The elementary forces dF on the actuator disks may becalculated using Blade Element Theory.

If the upwind and downwind interference factors are de-fined as

aV V

Va

V VVu

ud

d��

���

�(3)

the mathematical problem can be reduced to the calculationof au and ad. Because of the non-linearity of the equations, theproblem must be resolved iteratively. If the rotor blades havea fixed pitch angle or an assigned pitch variation (i.e. sinusoi-dal like in Pinson, cycloidal, etc.), the mathematical model isreduced, for each elementary streamtube, to an equation forthe momentum balance for the upwind actuator disk and anequation for the momentum balance for the downwind actua-tor disk.

� ��a asen

VV

C senu uRu

lu u( ) ( ) tan11

82

2

� ��

� � �

��

�� � �

� ��C

a a asen

VV

du u

d d uRd

cos ( )

( )( )

tan2

1 21

8

� � �

� �

� � ��

��

� �

� �

2

C sen

C

ld d

dd d

( )

cos( )

tan

tan

� �

� �

(4)

If the rotor blades have a self-acting variable pitch angle[3], [4], [5], another equation is also necessary for each actua-tor disk: the hinge moment equilibrium. In this case, in fact,the blade is partially free to pitch under the action of the aero-dynamic and inertia forces so as to reduce the angle of attack

78 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/

Acta Polytechnica Vol. 45 No. 3/2005 Czech Technical University in Prague

Downwind disk

d�d

�i

j

u

Upwind disk

Elementary streamtube

Circular path of

the blade

V V

Downwind disk

dAddAu

V V

Upwind disk

V

dFu dFd

V

V

V V

V

V

V

d�

Fig. 1: Double multiple streamtube model

Page 3: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

and hence the tendency of the blade to stall. The allowed an-gular swinging of the blade is limited by the presence of twoblocks. In this way the mathematical model is represented bytwo systems of equations, each constituted of two equations:momentum balance and hinge moment equilibrium. For oneblade and for the upwind actuator disk

a asen

VV

Cu uu

Rulu u zvu u( ) ( , ,Retan1

18

2

� ��

��

�� ��

)

( ) ( , ,Re )

cos( )tan tan

tan

� � �

� �

sen C

C

� � � �

� �

u u du u zvu u

u u

mc u zvu u nu u zvu u

c cer

4

4

( , ,Re ) ( , ,Re )

( )tan tan� � � ��

� �

C

x x �

� � � �

cos

( , ,Re )( )

tan

� �

zvu

tu u zvu u

c cer zvu

Cx x sen4 0

(5)

For the downwind actuator disk

( )( )

( ,tan

1 21

8

2

� � ��

�a a a

senVV

C

d d ud

Rd

ld d z

� �� vd d

d d dd d zvd d

d

,Re )

( ) ( , ,Re )

cos(tan tan� � �

� �

sen C� � � �

� � �tan

tan tan

)( , ,Re ) ( , ,Re )

(

d

mc d zvd d nd d zvd d

c

C C

x4

4

� � � ��

� � �

� � �

x

Cx x sen

cer zvd

td d zvd d

c cer

) cos

( , ,Re )( )

tan

� �

�4 zvd � 0

(6)

The instantaneous torque and power produced by theblade are given by the moment equilibrium around the tur-bine axis

� �M N x x

T R x x sen

P M

� �

� � �

� �

( ) cos

( )

c hinge zv

c hinge zv

4

4

(7)

To obtain the mean torque and mechanical power pro-duced by Nb blades in a revolution it is necessary to averagethe instantaneous values.

�MN

x x

T R x x sen

mb

c hinge zv

c hinge

� �

� � �

�2 4

0

2

4

��

( ) cos

( )� ��zv d ,�

(8)

�PN

x x

T R x x sen

mb

c hinge zv

c hinge

� �

� � �

��

2 4

0

2

4

��

( ) cos

( )� ��� �zv d .

(9)

To simulate dynamic performances, we have to resolveonly the equation of the moment equilibrium around turbineaxis (10) for fixed blade or Nb�1 equations for Nb floatingblades around their hinge axis (11).

I M MT ii

N�� � �

�� C

b

1

(10)

I M

I M

I

P zv1 h1

P zv h2

P zv

(�� ��)

(�� ��)

(�� ��)

� �

� �

2

3 �

� �

M

I M

h3

P zvn hn

(�� ��)�

(11)

3 Airfoils and aerodynamiccharacteristicsThe rotor performances were tested using five airfoils:

three symmetrical airfoils NACA 0012, 0015, 0018 and twocambered airfoils NACA 4415 and HLIFT18. The last namedwas designed at DPA; it is a high lift [6], [7] and no cavitatingairfoil. It has in fact been designed to work in the water on theKOBOLD turbine. For the NACA airfoils, data was taken fromthe literature [2], [8] while for the HLIFT18 airfoil, TBVOR[9], [10], [11] codes were used to generate the values of theaerodynamic coefficients. The airfoil 2D data is corrected, inVAWT and VAWT_DYN codes [12], to take into account thethree-dimensional effects due to the blade finite aspect ratio.To take into account the three-dimensional effects, Prandtl’slifting line theory, extended to treat high lift flow, has beenused, evaluating in this way the 3D lift curve beginning fromthe 2D data. This theory is valid only in the linear zone of thelift curve but with care it can also be extended to non linearconditions. The total blade drag coefficient is the sum of theairfoil drag coefficient (Cd), due to skin friction, and theinduced drag coefficient. To take into account the inter-ference between the blade and the support arms, a furtherdrag coefficient increment, �CD, has been introduced. More-over, 2D post-stall modelling, based on the Viterna-Corrigancorrelation method, has been introduced to extend the 2Daerodynamic coefficients to this angle range.

© Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 79

Czech Technical University in Prague Acta Polytechnica Vol. 45 No. 3/2005

V

arm

�R

V

V

n

n

t

c

L

D

Mc/4

�zv

Fig. 2: Hinge moment equilibrium

j

i

Mh1

Mh2

Mh3

M �

MC

TI

�zv

:

Fig. 3: Torques on a Kobold turbine

Page 4: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

4 Experimental modelsThe reported experimental data is divided into two parts:

� Experimental data measured in the DPA wind-tunnel atthe University of Naples on a small straight-bladed cyclo-turbine, which was designed, developed and assembled atDPA [13];

� Experimental data measured in water on the “Kobold”prototype (real scale) [12], [14].

Both the DPA straight-bladed cycloturbine (Model A)and the “Kobold” prototype (Model B) will be described, asfollows. Both turbines have variable pitch blades with a self--acting system, made up of two balancing masses for eachblade. In this way, the centre of gravity of the blade can bemoved into its optimal position in order to optimize theglobal performance of the rotor, and, using two stops, thepitch blade range can be limited, as shown in Fig. 5.

Model A in the DPA wind-tunnel is shown in fig. 6. Usingdifferent stop positions, it was possible to test different pitchangle ranges, and while using different numbers of blades itwas possible to take into account different solidity [Nc/R] val-ues. Model A has the following geometric parameters:

number of blades tested 2, 3, 4, 6blade chord 0.15 m

blade airfoil NACA 0018blade span 0.8 mAspect Ratio 5.33radius 1.05 mnumber of radial arm 4, 6, 8, 12arm chord 0.05 msolidity 1 0.286solidity 2 0.428solidity 3 0.571solidity 4 0.857

80 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/

Acta Polytechnica Vol. 45 No. 3/2005 Czech Technical University in Prague

0 0.2 0.4 0.6 0.8 1

x/c

-0.2

-0.1

0

0.1

0.2

y/cNACA 0012

NACA 0015

NACA 0018

0 0.2 0.4 0.6 0.8 1

x/c

-0.2

-0.1

0

0.1

0.2

y/cNACA 4415

HLIFT18

-30 -20 -10 0 10 20 30

A lfa [deg]-1.5

-1

-0.5

0

0.5

1

1.5

2

C L NACA 0012

NACA 0015

NACA 0018

NACA 4415

HLIFT18

-30 -20 -10 0 10 20 30

A lfa [deg ]0

0.1

0.2

0.3

0.4

0.5

0.6

C D NA CA 0012

NA CA 0015

NA CA 0018

NA CA 4415

HL IFT18

Fig. 4: Airfoils tested and aerodynamic characteristics (Re � 10e6)

i

Stop

V�

Hinge

Stop

Pitch

Range

j

Fig. 5: Balancing mass and blade stops

Fig. 6: DPA straight-bladed cycloturbine (Model A)

Page 5: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

The “Kobold” prototype (Model B) lies out in the Strait ofMessina, close to the Sicilian shore, facing a village calledGanzirri, close to the lake of the same name, as shown inFig. 7.

In this site the peak current speed is 2 m/s (4 knots), thesea depth is 20 meters and the plant has been moored150 meters offshore. The current changes direction every6 hrs and 12 minutes, and the amplitude period is equal to14 days. A high lift airfoil, called H-LIFT18, is used for theblade sections and has been specially designed at DPA to becavitation free and to optimise the turbine performance.Two arms sustain each blade and the arms have been stream-lined using another ad hoc designed symmetrical airfoil. Theturbine has a very high starting torque, being able in this wayto start spontaneously, also with electrical load connected,without the need for any starting devices. The ENERMARplant is composed of the turbine rotor hanging under afloating buoy that contains the remaining mechanical and

electrical parts to deliver energy to the grid, as shown inFig. 7. The rotor has a diameter of 6 meters with 6 radial armsholding three blades with a five-meter span and with a chordof 0.4 m employing the H-LIFT18 airfoil leading to an aspectratio of 12.5 and to solidity � � 0.4. The acquisition data sys-tem is made up of a torque-meter, a tidal current speed-meterand an RPM counter all connected to a PLC that convertsanalog signals to digital data transferring them to a PC. Datahandling software has been developed to monitor the ac-quired data in real time. Fig. 8 shows some components of theacquisition data system. The PLC also acts as an electricalload controller to keep the turbine working always at its maxi-mum efficiency independently from the current speed.

5 Experimental testsFig. 9 and Fig. 10 compare the VAWT code numerical re-

sults with the experimental data measured on Model A, for

© Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 81

Czech Technical University in Prague Acta Polytechnica Vol. 45 No. 3/2005

Fig. 7: The Strait of Messina, the position of the plant and a picture of the plant

Fig. 8: The torque-meter, the PLC and the PC

0 100 200 300 400

Rotor Angular Velocity (rpm)0

50

100

150

200

250

Mec

han

ica

lR

oto

rP

ow

er

(W)

pitch range = 0° - 10°

blades = 2

Solidity = 0.256

experimental data

VAWT results

0 100 200 300 400

Rotor Angular Velocity (rpm)0

50

100

150

200

250

Mec

han

ica

lR

oto

rP

ow

er

(W)

pitch range = 0° - 10°

blades = 3

Solidity = 0.428

experimental data

VAWT results

Fig. 9: Experimental data and VAWT results (Model A)

Page 6: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

82 © Czech Technical University Publishing House http://ctn.cvut.cz/ap/

Acta Polytechnica Vol. 45 No. 3/2005 Czech Technical University in Prague

0 100 200 300 400

Rotor Angular Velocity (rpm)0

50

100

150

200

250

Me

ch

an

icalR

oto

rP

ow

er

(W)

pitch range = 0° - 10°blades = 4

Solidity = 0.571

experimental data

VAWT results

0 100 200 300

Rotor Angular Velocity (rpm)0

50

100

150

200

250

Mec

han

ica

lR

oto

rP

ow

er

(W)

pitch range = 0° - 10°blades = 6Solidity = 0.857

experimental data

VAWT results

Fig. 10: Experimental data and VAWT results (Model A)

1.6 1.8 2 2.2 2.4 2.6 2.8

TSR

0.12

0.16

0.2

0.24

0.28

0.32

0.36

Ne

tro

tor

pow

er

co

eff

icie

nt

experimental data

VAWT results

Fig. 11: Experimental data and VAWT results (Model B)

0 10 20 30 40 50

2

4

6

8

10

12

numerical

experimental

0 10 20 30 40 50

-40

0

40

80

120

160

To

rqu

e(N

m)

numerical

experimental

Fig. 12: Experimental data and VAWT_DYN results (Model B)

Page 7: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

different blade numbers and different pitch range. The pitchangle is measured between the local tangent to the bladecircular path and the blade trailing edge, starting from thetangent in clockwise direction. The power measured is the netrotor power, and the tests are carried out with 9 m/s air speedin the DPA wind tunnel for Model A. A comparison of thenumerical results with the experimental data shows goodagreement, especially for 3 and 4 blades; in the case of6 blades, the solidity is very high and there is a strong wakeeffect on each blade. Fig. 11 compares the experimental datameasured during field tests in water for the Kobold turbineprototype – model B – with the VAWT code numerical predic-tion. The net rotor power coefficient is measured, and thetests are carried out with a presumed current speed of 1.4 m/s,but there is uncertainty around 25 % on the real “undis-turbed” current speed value, which is strongly influenced bythe location of the current speed meter: this is at present be-ing investigated. Fig. 12 and Fig. 13 show the experimentaldata and VAWT_DYN code numerical results referred to thestarting condition for the Kobold turbine prototype (ModelB). The rotor angular velocity variation in time predicted bythe code seems to be very accurate, while the rotor torque andpower amplitudes are in good agreement only in the first partof the time range: this is probably due to the uncertain valueof the numerical predicted losses. The frequency of the torqueand power is, however, very well predicted.

6 ConclusionsThe Double Multiple Steamtube model seems to be good

in predicting the vertical axis turbine performances, withfixed or floating blades, expecially for solidity values lessthan 0.5. This model has been implemented in VAWT andVAWT_DYN codes, which are then capable of predicting bothstatic and dynamic performances of the turbine with very lowcomputing time. In these codes blade 3D effects have beenincluded as well as arm losses, while it is difficult to predict thelosses due to other effects. In the field tests, the accuracy ofthe tidal speed current measurement is a problem, becauseit is difficult to set the current speed-meter in the “real” un-disturbed flow, so the measurements have an uncertaintylevel around 20 %. On the Kobold turbine, the HLIFT18

non-symmetrical and non-cavitating airfoil gives better per-formance than a symmetrical airfoil, and the self-acting vari-able pitch system with balancing mass has proven to be simpleto build and more reliable than other more complex systems.

References[1] Strickland, J. H.: “A Review of Aerodynamic Analysis

Methods for Vertical-Axis Wind Turbine.” In: FifthASME Wind Energy Symposium, SED – Vol. 2 edited byA. H. P. Swift.

[2] Paraschivoiu, I.: Wind Turbine Design with Emphasis onDarreius Concept. Ecole Polytechnique de Montreal, Poly-technic International Press, 2002.

[3] Kentfield, J. A. C.: “Cycloturbines with Freely HingedBlades or Freely Hinged Leading Edge Slats.” In: Alter-native Energy Sources V. Part C: Indirect Solar/Geo-thermal. (Editor: T. N. Veziroglu). Amsterdam: ElsevierScience Publishers B. V., 1983, p. 71–86.

[4] Lazauskas, L.: “Three Pitch Control Systems for VerticalAxis Wind Turbines Compared.” Wind Engineering,Vol. 16 (1992), No. 5, p. 269–281.

[5] Kirke, B. K., Lazauskas, L.: “Experimental Verificationof a Mathematical Model for Predicting the Perfor-mance of a Self-Acting Variable Pitch Vertical AxisWind Turbine.” Wind Engineering, Vol. 17 (1993), No. 2,p. 58–66.

[6] Healy, J. V.: “The Influence of Blade Camber on theOutput of Vertical Axis Wind Turbine.” Wind Engineer-ing, Vol. 2 (1978), No. 3, p. 146–155.

[7] Healy, J. V.: “The Influence of Blade Thickness on theOutput of Vertical Axis Wind Turbine.” Wind Engineer-ing, Vol. 2 (1978), No. 1, p. 1–9.

[8] Reuss, R. L. et al.: Effects of Surface Roughness and Vor-tex Generators on the NACA 4415 Airfoil. Report:NREL/TP-442-6472. Golden, Colorado: National Re-newable Energy Laboratory, December 1995.

[9] Coiro, D. P., de Nicola, C.: Prediction of Aerodynamic Per-formance of Airfoils in Low Reynolds Number Flows. In: Low

© Czech Technical University Publishing House http://ctn.cvut.cz/ap/ 83

Czech Technical University in Prague Acta Polytechnica Vol. 45 No. 3/2005

0 10 20 30 40 50tim e (s )

0

4

8

12

Me

ch

an

ica

lp

ow

er

(kW

)

n u m e r i c a l

e x p e r im e n ta l

Fig. 13: Experimental data and VAWT_DYN results (Model B)

Page 8: Dynamic Behaviour of the Patented Kobold Tidal Current Turbine.pdf

Reynolds Number Aerodynamics Conference, NotreDame, Indiana, U.S.A., June 1989.

[10] Coiro, D. P., de Nicola, C.: “Low Reynolds NumberFlows: The Role of The Transition.” In: X CongressoNazionale AIDAA, Pisa, Ottobre 1989.

[11] Coiro, D. P.: “Convergence Acceleration Procedure for aViscous/Inviscid Coupling Approach for Airfoil Perfor-mances Prediction.” In: XI AIDAA National Congress,Forli’, Italy, October 1991.

[12] Montella, F., Melone S.: “Analisi Sperimentale e Nume-rica del Comportamento Statico e Dinamico di unaCicloturbina ad Asse Verticale.” Aerospace EngineeringBachelor Thesis. Napoli, Italy: Dipartimento di Proget-tazione Aeronautica, December 2003.

[13] Coiro, D. P., Nicolosi, F.: “Numerical and ExperimentalTests for the Kobold Turbine.” In: SINERGY Sympo-sium, Hangzhou, Republic of China, November 1998.

[14] Coiro, D. P. et al.: “Exploitation of Marine TidalCurrents: Design, Installation and Experimental Resultsfor the Patented Kobold Vertical Axis Hydro Turbine.”

In: Poster-Session OWEMES 2003. Napoli, Italy,10–12 April 2003.

Prof. D. P. Coirophone: +39 081 7683322fax: +39 081 624609e-mail: [email protected]

Dr. A. De Marcoe-mail: [email protected]

Dr. F. Nicolosie-mail: [email protected]

Dr. S. Melonee-mail: [email protected]

Dr. F. Montellae-mail: [email protected]

Dipartimento di Progetazione Aeronautica (DPA)University of Naples “Federico II”Via Claudio 21, 80125 Naples – Italy

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Acta Polytechnica Vol. 45 No. 3/2005 Czech Technical University in Prague