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International Journal of Mechanical & Mechatronics Engineering IJMME-IJENS Vol: 11 No: 01 16

115301-7474 IJMME-IJENS © February 2011 IJENS I J E N S

Design and Blade Optimization of Contra Rotation Double

Rotor Wind Turbine

Priyono Sutikno1, Deny Bayu Saepudin

2

1Institut Teknologi Bandung, Bandung, Indonesia, [email protected]

2Institut Teknologi Bandung, Bandung, Indonesia, [email protected]

Abstract - The Intelligent Wind turbine (IWT) has two stagesblades contra rotation. This kind of wind turbine hascharacteristic self regulated on the speed due to thedifference torque between two stages horizontal axis wind

turbine, than no need the pitch controller to control thespeed and cut off the wind turbine due to the high wind

speed.The research of IWT is designed first by optimize severalimportant design parameters, as a blade section profile and

the multiplier factor of the angle of attack. The designparameter results are the NACA 6412 is selected as the

optimum blade section profile and the optimum value of angle of attack multiplier factor is 0.5. The designed IWThas 3 blades for each front and rear rotor. The researchintelligent wind turbine has 600 mm front diameter and 600

mm rear blade diameter. The characteristics of IWT weresimulated by using Computational Fluid Dynamic (CFD)

software, demonstrated the non entrainment of the contrarotation, each blades should have the same produced torque.

Index Terms – Intelligent Wind Turbine, NumericalSimulation, Contra rotation Wind Turbine

I. INTRODUCTIONThe conventional wind turbines with large sized wind

rotor generate high output in the moderately strong wind.The output of the small sized wind rotor is low such awind rotor is suitable for weak wind. That is, the size of

the wind rotor must be appropriately selected inconformity with potential wind circumstances. Besides, ingeneral the wind turbines are equipped with the brake andor the pitch control mechanisms, to control the speed dueto the abnormal rotation and the overload generated at thestronger wind, and to keep the rotation of generator. Inthat sense, some studies present a good review of various

invented the superior wind turbine generator, T.

Kanemoto [1] has invented Intelligent Wind TurbineGenerator (IWTG) composed of the large sized front wind

rotor, the small sized rear wind rotor and the peculiargenerator with inner and the outer rotational armatures, asthe rotational speeds of the tandem wind rotor areadjusted pretty well in cooperation with the two armatures

of the generator in response to the wind speed. The IWTGmodel is composed of tandem wind rotor using the flatblades, and demonstrated the fundamentally superior

operation of the tandem wind rotor. In this paper, theeffect of the blade profiles using NACA profiles on theturbine using numerical simulation on the turbineperformances are investigated to optimized the rotor

profiles.

Nomenclature A Area

a Axial induction factora’ Radial Induction factor B Number of blade

C D Drag coefficient

C L Lift coefficient

c Chord length

C p Power Coefficient D Diameter

F x Axial Force

g Acceleration of gravity L Lift forceP Power

p pressureQ correction factorr local radius element rotor

Re Reynolds number

R RadiusT Torsi

T ∆ Thrust

V o Absolute Velocityw Relative velocityu Tangential velocity

x Local speed ratio

α angle of attack (AOA) β stagger anglee Ratio coefficient Lift and Dragγ pitch angelη Efficiency λ Tip speed ratio ρ density

φ angle of attack relative

σ SolidityΩ Angular velocity

II. OPERATION OF TANDEM WIND ROTORSIn the IWTG both wind rotors start to rotate at low

wind speed, namely cut in wind speed, but the rear wind

rotor counter rotates against the front wind rotor. Theincrease of the wind speed make the both rotationalspeeds increase, and the rotational speed of rear wind

rotor becomes faster than that of the front wind rotorbecause of its small size. The rear wind rotor reaches themaximum rotational speed at rated wind speed. With

more increment of the wind speed, the rear wind rotordecelerates gradually and begins to rotate at the samedirection of the front wind rotor so as to coincide with

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larger rotational torque of front wind rotor. Suchbehaviour of rear wind rotor is induced from the reasonwhy the small sizes wind rotor must work as the blowingmode against the attacking wind because the wind rotor

turbine mode can \not generate adequately the rotationaltorque corresponding to the front wind rotor. The

behaviour of the front and rear wind rotors also dependson the blade profiles and flow condition between bothrotors, and will be discussed. The rotational direction andspeed of the rotors are adjusted in response to the windcircumstance (see figure 2)

Fig. 1 Drawing IWTG [1]

Fig. 2 Operation of IWTG [1]

The authors has proposed the optimized blades withadopted the NACA Air foils for rear and front blades of

the contra rotation wind turbine. It is difficult, however toknow the rotational torque but also to get optimizedblades profiles, using the contra rotation model. In orderto elaborate and to get the optimized blades, the model

was separated from tandem to single isolated wind turbine,however the rear turbine has the velocity data’s from thefront wind turbine blade simulation.

III. AIR FOIL AND ROTOR PERFORMANCE

ANALYSIS.

Airfoil has made rotor possible to rotate in high speed

and load, early aerodynamics of wind turbine has based

on theory of air plane wings. However, aerodynamics of wind turbine has been required different idea, the

accuracy of rotor performance analysis depend mainly on

the treatment of the wake effect, because the wake of propeller type wind turbine is induced a large velocity inrotor plane. For Horizontal Axis Wind Turbine blades the

aviation airfoils such as NACA series have been widelyused. But these air foils have been recognized to beinsufficient for requirements, such reduction of rapid stall

characteristics, in-sensitivity to wide Reynolds numberthe range of between 5.10

5to 2.10

6. Rotor performance

analysis has been performed using several methods. TheBlade Element Momentum (BEM) method is mainlyemployed as a tool of performance analysis because of

their simplicity and readily implementation. Vortex wakemethods can adequately treat the effect of wake vorticesand have some advantages over BEM.

3.1 Blade Element Momentum MethodMost wind turbine design codes are based on Blade

Element Momentum (BEM) method [7]. The basic BEMmethod assumes the blade can be analyzed as a number of

independent elements in span wise direction. The inducedvelocity at each element is determined by performing themomentum balance for an annular control volume

containing the blade element. The aerodynamic forces onthe element are calculated using lift and drag coefficientfrom empirical two dimensional wind tunnel test data atthe geometric angle of attack (AOA) of the blade element

relative to the local flow velocity.BEM method have aspect by reasonable tool for

designer, but are not suitable for accurate estimation of effect of wake, complex flow such as three dimensionalflow or dynamic stall because of their assumption.

3.2 Vortex Wake MethodThe induced velocity in the rotor plane of Horizontal

Axis Wind Turbine (HAWT) is largely increased in heavyloading condition and the wake vortices of HAWT

develop to the downstream constructing highly skewedvortex sheet in largely decelerated axial flow near rotorplane. Thus determination of the velocity induced bywake and wake geometry is one of the most important

aspects in the rotor performance analysis.Vortex wake method directly calculates the induced

velocity from the bound vortices of blades and the trailing

vortex in wake which are represented by lifting line orlifting surface model [4]. The treatment of wake geometry

can be classified roughly into two type, as a prescribedwake model and free wake model. In the former model

the wake represented by a line a vortex or spiral vorticeswith fixed pitch. In later one a fractional step scheme isadopted and the configurations of the wake are calculatedat every time step using local velocity including the

components induced by wake and bound vortices. Thefree wake model is generally tackled with vortex latticemethod which can fit on arbitrary blade shape with

camber, taper and twist.Another method of the vortex wake methods is use of

an asymptotic acceleration potential. Accelerationpotential method is basis on the Laplace equation of

pressure perturbation. The rotor blades are represented inthe model as discrete surfaces on which a pressure

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discontinuity is present. The model implies the presenceof span wise and chord wise pressure distributions, whichare composed of analytical asymptotic solution forLaplace equation. More elaborate model makes it possible

to calculate the dynamics load caused by dynamic inflowand yawed inflow situation [5].

3,3 Computational Fluid DynamicRecent development of the computational fluid

dynamics (CFD) allows us to simulate overall flowaround HAWT including tower and nacelle. In 1999

Duque et al. [6] calculated aerodynamics of HAWT usingRANS model and overset grids to facilitate the simulationof flow about complex configuration. Recently, someCFD’s codes actively are developed of CFD analysis of

rotor flow by three dimensional Navier Stokes code.Though the state of the art CFD is needed

considerable computer power and validation for NavierStokes model, CFD has potential advantage for detailed

understanding of aerodynamic of the HAWT.

IV. OPTIMAL ROTOR BLADE

4.1 The NACA series air foilThe design model, which is composed of tandem wind

rotor, designed based on Blade Element Momentum

(BEM) method. The design is used the 4 (four) digitNACA airfoil and to be chosen among 7 (seventh) airfoilprofile as shown at figure 3.

A : 1st

digit is the percent of chordB : 2

nddigit is the ten percent of the chord

C : 3rd

and 4th

digit is the percent of chord

Fig. 3 Airfoil Profile of 4 digits NACA XXXX

The criteria of NACA airfoil to be implemented to thefront rotor and rear rotor, the XFOIL software is used to

simulated the Lift and Drag Coefficient at function of AOA, the criteria’s are

a. The airfoil has a good performance, should haveas bigger as possible the ratio of the ratio the Liftand Drag coefficients as shown at Table 1.

b. The section of the airfoil has simple form

possible, which has a flat suction in order tosimply the blades manufacturing, see Fig. 3.

Table 1.The maximum Lift and Drag ratio of NACA 5 and 6

series

Beside the Lift and Drag Ratio, the camber to chord ratiocan be influenced the Lift to Drag Ratio, and as shown atfig. 4. The NACA airfoil has been chosen, have a certain

AOA at the maximum Lift to Drag Ratio.The number of blades at the front and rear rotor dependon the velocity to tip ratio as shown at table 2 [5]. Therotation of the front and rear rotor depend on the tip speedratio, for tip speed ratio between three and more than four,

the number of rotor is three.

Table 2 The number of blade depend on speed tip ratio λ

λ B [number of blade]

1 8 – 24

2 6 – 12

3 3 – 64 3 – 4

More than 4 1 – 3

The rotor performance analysis of IWT has beencalculated by the model Actuator Disc and Blade Element

Momentum. This method has been modelled anddeveloped by Glauert (Ingram, 2005), the inflow near therotational blade or disc as the induced velocity in the rotorplane is largely increased and represent by rotational

inflow factor.The aerodynamic forces on element are calculated usingthe lift and drag coefficient from XFOIL software.

Fig. 4 The Lift to Drag ratio of the NACA XXXX series

The optimum blade can be concluded by comparing thedata on table 1 and performance of blade in the figure 1

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and 4 with respect to the criterion above, the chosen bladehas thickness to chord ratio of 12%, the camber to chordratio is 6% and the air foil NACA 6412 is chosen asairfoil for front and rear rotor.

4.2 Optimal rotor blade using GLAUERT-PRANDTL-

XU model.The calculation is based on the Blade Element

Momentum (BEM) method, this method is suitable forengineering development and there are two kinds of categories: fixed pitch and variables pitch rotor blade. The

blade length is divided into several small elements forwhich the two dimensional airfoil theory can be applied.The dimensionless coefficient, C L and C D, the net force,power and torque caused by B blades, each of local chord

c, are as follow [6]:

For torque:

[ ] Bc Δccos DC sin LC r 2 ρW 21 ΔQ φ φ −= (1)

For power:

[ ] r Bccos D

C sin L

C r 2

W 21QP ∆φ φ Ω ρ Ω∆∆ −== (2)

For thrust:

[ ] r Bcsin DC cos

LC

2W

2

1T ∆φ φ ρ ∆ += (3)

whereφ sin

uW = =

( )φ

Ω

cos

wr +

Fig. 5 Local element velocities and flow angles [8]

Based on actuator disc theory and Using dimensionless

axial and radial induction factor,( )

0

0

V

uV a

−= and

r

w' a

Ω = and solidity,

R

Bc

π σ = we find equation above

became

Fig. 6 Local elemental forces [8]

( )

+

=

− φ

φ φ σ 2

D L

sin

sinC cosC

r 8

R

a1

a (4)

( )

−

=

+ φ φ

φ φ σ

cossin

cosC sinC

r 8

R

' a1

' a D L (5)

Also we have

wr

utan

+=Ω

φ ( )( )' a1r

a1V 0

+

−=Ω

( )( )' a1 x

a1

+

−= (6)

where, x =0

V

r Ω , is local speed ratio. At the end of the

blades, r become R, and we find the most importantparameter for wind turbine rotors, the tip-speed-ratio,

or0V

R X

Ω = , using X , we can

write,( )( )

+

−

=

' a1

a1

rX

Rtanφ , the two dimensional lift

and drag coefficients CL and CD are both function of angle

of attack φ and

L

D

C

C =ε , Instead of using the average

solidity, it’s define a symbol called the blade loading

coefficient,r .8

Bccl

π λ = , using λ and ε we obtain

( )

+=

−φ

ε φ λ

sin

cot

a1

a (7)

And

( )

−=

+ φ

ε φ λ

sin

tan

' a1

' a(8)

To obtain a single point optimum including the effect of

drag, deriving a local power coefficient [6],

3

0

D L

2

3

02

1

'

PV 2

)cosC sinC ( BcW

AV

PC

π

φ φ

∆ ρ

∆ −== (9)

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where,

[ ] dr BccosC sinC Ωr ρV ΩdQdP D L

2

total2

1 φ φ −==

and dA =2 π dr by using :

( ) ( )222222

totala1r a1U V ′++−= ∞ Ω and equation 6, then

equation 9 can be write

( ) ( ) ( )φ φ cosεφsin x λ4cot 1a1C 22

p−++−=′

(10)

Then, eliminating λ using equation 7 and expanding 1/(cot

φ + ε) in a Taylor’s series of two terms, there results

( )( )( )φ ε ε φ tan1tana1 xa4C p

+−−=′ (11)

Since the optimum value of a is founded to be quite

insensitive to changes in ε, this implies that pC′ decreases

monotonically as ε increases. By defining a local Froude

efficiency (Eq. 12), we can relate the performance of each

blade element to the ideal value of unity [6].

pF C 16

27 ′

=η (12)

The correction factor for total losses can actually be quitewell represented by Prandtl and Xu represent the tiplosses and hub losses, the equation is quite simple but can

give the good matched on HWAT (Horizontal Axis WindTurbine) [10], the Prandtl tip correction factor is

( ) 12cos exp 7tip tip tipQ f if f

π

−= − ≤

1 7tip tip

Q if f = >(13)

( )2 sin

tip

B R r f

r φ

−=

And for hub correction factor can be written as

( ) 12cos exp 7

hub hub hubQ f if f

π

−= − ≤

1 7hub hubQ if f = >

(14)

( )2 sin

hub

hub

hub

B r R f

R φ

−=

Early 2001, Xu proposed the correction factor on hublosses by using the Prandtl correction factor as writtenabove and the Xu correction factor for hub can be written

as

( )( )0,85

0,5 0,5 0, 7 1new

tip tipr Q Q if R

= + ≤ ≤(15)

( ) / 0,71

1 0.70,7

tipr Rnew

tip

r Qr Q if

R R

=−

= − <

Flowchart in figure 7 explained the complete proceduresof rotor turbine design. This flow chart refers to optimumdesign procedure of rotor blade and the source program is

written in FORTRAN code, while XFOIL is used toobtain the Lift coefficient and Drag coefficient of airfoildata which is chosen for blade design. After obtaining theLift and Drag Coefficients an interpolation is performed

to justify Reynolds number and angle of attack (AOA) oncalculation XFOIL or two dimensional flow over the

airfoil by Fluent.

Fig. 7 Flowchart to calculate forces and power at the

optimum performance

Wind turbine rotor with three blade formed by several

airfoil profile with smaller chord length from hub to tipevery blade along the span. Figure 8 displayed graphic of

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Fig. 8 Graphic of distribution of chord length and twistangle at rotor span

chord length and stagger angle in function of angle of

attack (AOA).Figure 9 shown graphic of the torque and the efficiencycurve versus the rotational speed and the figure 10 shown

graphic of the torque and efficiency versus rotationalvelocity results of the numerical simulation using theFLUENT software. Figure 11 shown graphic of theefficiency as functions of the velocity source calculated

manually and simulated three dimensional numericallyusing the FLUENT.

Fig. 9 Graphic of torque versus rotational speed calculatedand simulated numerically

Figure 8 to 9 shown the graphics of chord length versusspan length of rotor, the torque versus rotational speed

and the efficiency versus rotational speed respectively,these results has been calculated by PRANDTL-XUcorrection equation and simulated numerically using the

FLUENT 6.3.26. We can concluded the optimum

performance is used the angle of attack with α 6 ,0 to be

chosen with regard of

• The Maximum efficiency is near of the working or

design point at the rated rotation

• The produced torque has relatively high

• The values of the efficiency of the wind speedregion (2 until 12 m/s) are always relatively high

and stable as shown at figure 11.

Fig. 10 Simulation result using the Blade ElementMomentum and Prandtl_Xu correction factor on efficiency

versus rotational speed

The optimum blade is NACA 6412, blade has thickness tochord ratio of 12%, the camber to chord ratio is 6% and

the angle of attack is α 6 ,0 multiplier.

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Fig. 11 The efficiency versus wind speed

V. DESIGN AND SIMULATION OF THE IWT

5.1 Design Procedures for Wind Turbine Rotor

Flowchart in figure 7 explained the completeprocedures of rotor turbine design. This flowchart refersto optimum design procedure of rotor blade, and thesource program is written in EXCELL code, while theXFOIL or FLUENT software is used to obtain lift

coefficient (CL) and drag coefficient (CD) of airfoil datawhich is chosen for the blade design. After obtaining thelift coefficient (CL) and drag coefficient (CD), aninterpolation is performed to justify Reynolds number and

angle of attack on calculation.

5.2 Simulation Procedures for Intelligent Wind

Turbine Front and Rear Rotors

The simulation of Intelligent Wind Turbine front andrear rotors are using computational fluid dynamic (CFD)method through Fluent software. The simulation process

consists in two parts, the two dimension model and threedimension models. Two dimension model is usingFLUENT DDP to calculate lift coefficient (CL), dragcoefficient (CD), pressure coefficient and flow

characteristic through airfoil profile in two dimension,while Fluent 3D is used to calculate force componentswhich rotor produced and flow characteristic in threedimension, especially flow behind the rotor which shown

velocity decrease and wind energy, turbulence, and wake.The two dimension simulation proposed to obtain airfoil

characteristics which will be used in blade design withangle of attack variation and Reynolds number variations,then served as an input on blade design by usinginterpolation. The airfoil profile has been calculated andsimulated at section 4.

Two dimension simulation process is completed byGambit meshing around 66.000 cells and iteration usingFLUENT 2DDP with assumption of compressible flowand coupled solver was used including energy calculation

using absolute velocity formulation in steady condition.These assumptions are requisite in order to obtainaccurate current model on airfoil surface by showing

turbulence phenomenon, flow separation, boundary layer,

and reversed flow. This flow phenomenon is their natural

flow characteristic, where the decreasing of whole airfoilperformance and rotor efficiency in extreme situation [9].

The result of calculation for the front and rear rotor

can be shown as bellows:

Fig. 12 Result of distribution of chord length (c) of thefront and rear rotor span of IWT

Fig. 13 Result of distribution of pitch angle of the front

and rear rotor span of IWT

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Fig. 14 The front at the left figure and rear rotor at the right

5.3 The three Dimensional Model Simulation of the

IWT front and rear rotor.The analyzed aerodynamic problem is flow detriment

including wake around rotor, distribution of velocity andpressure decrease in axial direction. The first simulation ismade to a front rotor with 60 cm diameter which placed in

a cylinder wind tunnel with 150 cm diameter and 300 cmlength. Flow condition is steady, front rotor speedconstantly at 600 rpm and tip speed ratio of 3.142 wind

condition for rear rotor can show at figure 15.

Fig. 15 Position of the pickup velocities and pressures fromthe front rotor blade

directions are assumed uniform velocity input before hitsthe rotor. The second simulation is made a rear rotor with60 cm diameter, the boundary condition of the input rearblade are the velocity vectors output from the first

simulation of the front blade. The pickup boundaryThree dimension wind turbine rotor is produced using

3D Inventor modeling program (Inventor 2008) version.

Blade is made of several airfoil profiles along the spanusing blend method to form blade with twist pattern,previously these airfoil profiles were kept in *.sec format.Afterwards, the blade making result that produced by

Inventor 2008 are exported to Gambit in *.igs format.

Fig. 16 Intelligent Wind Turbine, the front and rear bladesin isometric and front view

Modeling process in Gambit is making meshingaround 6.0 million cells (TGRID) and defining boundaryconditions. Modeling in Gambit taking the wind tunnel

analogy as boundary conditions, and there is only onevolume control around rotor as rotating frame. In Fluent,the finishing process is using segregated solver model

Front rotor

Axis of rotor

Rotor axis

Blade 3Blade 2

Blade 1

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with relative velocity formulation or multiple referenceframes (MRF) model and steady conditions. It isimportant to do the relative velocity formulation becausethe volume control that used is rotating frame (non

inertia) [2], in order to analyze relative velocity impact toa rotor and exposed current flow behind the rotor (wake)

[9]. The expected result in 3D simulation is to get far flowaround rotor, not just only at the rotor surface. Theapplied viscous model is the same model that applied in2D simulation which is viscous k-ε model [8], [10].

VI. RESULT AND DISCUSSION

Two dimension and three dimension rotor turbine areanalysis using optimum blade design and calculated withBET PRANDTL-XU methods or designed and simulated

by 3D Fluent indicates a good results and have samesimilitude. If we compare both analyses result by fluentand by BET PRANDTL-XU methods, it turned out that

there is only small difference on calculation results of resultant velocity. It is showed by calculation result of velocity resultant distribution along the blade shown atfigure 9 and 10, where the torque is 17 Nm and the

efficiency is 35% at 500 rpm and by using numericalsimulation Fluent, the torque is 0.14 Nm and theefficiency is 30% at 500 rpm. The same way theefficiencies calculated by both methods has a same tend.

Fig. 17 Simulation result of the torque and efficiency curveof the front and rear rotor IWT

The BET-PRANDTL-XU method has been used for thefront and rear rotors optimum design condition andproduced the front and rear rotor blades as shown atfigure 14 above. The numerical simulation used FLUENT

to get the performance shown at figure 17 is the numericalsimulation result give the torque and the efficiency curves

in function of rotation speed of the both rotor, front andrear rotor blades. The simulation is conducted by separatethe front rotor as a single wind turbine. To get the resultof rear rotor numerical simulation, the boundary conditionshould be setup from the output of the front rotor

numerical simulation. The boundary condition for the rearrotor has been taped as shown at figure 15, there areseveral pick up data’s in the radial direction and data’s atdirection of flow in the upstream and downstream as we

can see at z1, z2 and z3. The pickup data at radial directionare indicated by raw r1 until r5. The 3 dimensional IWTdesign can be seen at figure 16, the front rotor has 3 blueblades and the rear blade rotor has green color. The result

of numerical simulation using the FLUENT has results asshown at figure18, the efficiency curve of IWT versuswind velocity and figure 19 shown the characteristic of

the rotational velocity relative of the front and rear bladesdepend on the wind velocity.

Fig. 18 Efficiency Curve of IWT

Fig. 19 IWT Rotational speed versus wind speed

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In the classical wind turbine, there are two ways incontrolling the output of wind turbine power, they are:1. Blade pitch controlled wind turbine2. Stall controlled wind turbines; passive stall controlled

wind turbines and active stall controlled

On the Intelligent Wind Turbine (IWT) with contrarotation rotor blades has speed adjustment depend on thewind speed as shown at figure 17. The IWT both rotorsstart to rotate at low wind speed, namely cut in windspeed, but the rear rotor contour rotates against the front

rotor. The increase of the wind speed make the bothrotational speeds increase, and the rotational speed rearrotor become faster than that of the front rotor. At windspeed of 4 m/s the rotational of front rotor is 400 rpm and

rotational speed of rear rotor is -400 rpm and until windspeed of the 6 m/s, the rotational of front rotor is 600 rpmand rotation of rear rotor is -500 rpm, that means therelative rotational velocity is 1100 rpm and IWT has

maximum efficiency of 27%.At the wind speed more than 7 m/s, the rotational speed of rear rotor decreased until the wind speed 11.5 m/s, the

rotation speed direction of both rotor, front and rear rotorshas a same direction but the relative rotational speedremain same is 1100 rpm.

VII. CONCLUSION

The IWT which composed of tandem rotors andcontra rotation has characteristic superior as theconventional wind turbine, than no need pitch control orstall control to controlling the rotational speed when wind

speed became too high. The IWT can start rotate on weak wind speed. At moderate wind speed IWT can rotated

relatively on adequate rpm, because the IWT has contrarotation rotor. When the wind speed increased, therelative rotational speed remain constant, event at high

wind speed the relative rotational speed remain constantabout 1100 rpm, the rear rotor has been entrainment bythe front rotor and rotated at same direction.

The numerical simulation was demonstrated thedirection of the rotation of both front and rear rotor shouldhave a same order torque. The method to get the optimumblade profile and the numerical simulation can be used as

preliminary design and to get the estimated characteristicof contra rotation blade span.

ACKNOWLEGMENT

This works was supported by Riset Unggulan 2010 LPPM(Research and Service to the Community Institute)INSTITUT TEKNOLOGI BANDUNG.

REFERENCES

[1] Toshiaki Kanemoto. and Ahmed Mohamed Galal.2006. Development of Intelligent Wind TurbineGenerator with Tandem Wind Rotor and Double

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[2] Dahl K. S., et al., Experimental Verification of the

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[3] Wilson, R.E., and Lissaman, P.B.S., AppliedAerodynamics of Wind Power Machine, NTIS PB

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[6] Duque, E.P.N., et al., Navier-Stokes Analysis of TimeDependent Flow about Wind Turbine, Proc. Of 3

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