H Darrieus Turbine

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Proceedings of the 37th

International & 4th

National Conference on Fluid Mechanics and Fluid Power

FMFP2010

December 16-18, 2010, IIT Madras, Chennai, India

FMFP2010________

PERFORMANCE MEASUREMENT OF A TWO-BLADED H-

DARRIEUS TURBINE MADE FROM FIBREGLASS

REINFORCED PLASTICS (FRP) BLADES

HPDLODJQLELV#\DKRRFRLQ HPDLOUBJXSWDQLWVLO#\DKRRFRP

ABSTRACT

Vertical Axis Wind Turbine (VAWT)

has got many advantages, like simple in

construction, omni-directional, self-

starting, low wind applications etc,

which make VAWT a viable

proposition for functions like pumping,

irrigation, grinding etc. However,

VAWT is not gaining popularity largely

due to its low efficiency. In this paper,

the power coefficient (Cp) of a two-

bladed H-Darrieus turbine made from

Fibreglass Reinforced Plastic (FRP)

blades was measured in a subsonic wind

tunnel for height-to-diameter (H/D)

ratios of 0.85, 1.0, 1.54 and 1.72. Three

types of wind tunnel blockages, namely

solid, wake and sidewall blockages

were considered for measuring Cp. Cp

increased with the increase of H/D ratio

up to the maximum, and then decreasedeven if H/D ratio was increased. Thus,

there was an optimum H/D ratio for

which Cp was the maximum. And the

maximum Cp of 0.267 was obtained at

an optimum H/D ratio of 1.0.

Keywords: Two-bladed FRP, tip speed

ratio, wind tunnel blockage, power

coefficient, H/D ratio

INTRODUCTION

Wind energy is the most prolific

alternative source of energy for power

generation. The rise in the demand for

wind energy is reflected in the

increasing growth of wind-based energy

systems all over the world. Global WindEnergy Council (GWEC) has predicted

that the global wind market will be

growing by over 155% from its current

size to reach 240 GW of total installed

capacity by the year 2012. According to

the figures released by GWEC (GWEC,

2009), the five top countries in terms of

installed wind power capacity are USA

(35,159 MW), Germany (25,777 MW),

China (25,104 MW), Spain (19,149

MW) and India (10,926 MW). Wind

turbine is the heart of any wind-based

energy system. Though most of the

wind turbines in the present era are

HAWT type, but VAWT has got

definite role to play especially in low

wind speed condition. The VAWT

Agnimitra BiswasLecturer (Contract), Deptt. of Mechanical Engg.,

NIT SilcharNIT Silchar, Assam, India

Rajat GuptaProf. (Mech. Engg) & Dean (R & C), Deptt. of

Mechanical Engg., NIT SilcharNIT Silchar, Assam, India

Proceedings of the 37th National & 4th International Conference on Fluid Mechanics and Fluid Power

December 16-18, 2010, IIT Madras, Chennai, India.

FMFP10 - TM - 23


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could be a viable proposition for small-

scale applications in the remote areas of

any developing country (Islam et al.,

2005). But the major problem with

VAWT is its low power coefficient.

Thus, the challenge lies in designing aVAWT having high power coefficient.

There are at present several

VAWT models commercially available

such as Savonius turbine, Darrieus

turbine, H-Darrieus turbine etc. S.J.

Savonius, a Finnish scientist, developed

Savonius turbine initially in 1929

(Savonius, 1931). Savonius tested about

30 different models of the turbine in the

wind tunnel. The best model showed apower coefficient (Cp) of 31%. The

eggbeater Darrieus wind turbine was

originally invented and patented by

Georges Jean Marie Darrieus, a French

aeronautical engineer, (Darrieus, 1931).

H-Darrieus turbine was included in the

same patent of 1931. The major

problem with eggbeater Darrieus

turbine or Savonius turbine is that of

stall at increased wind speeds created bythe blade moving out of the wind in the

downstream side. This limits the speed

that the advancing blade can propel the

whole rotation forward. However, H-

Darrieus turbine is self-regulatory at all

wind speeds (Islam et al., 2005). The

H-Darrieus turbine has two or three

blades designed as airfoils, which are

attached vertically to the central shaft

through support arms. The support to

vertical axis helps the turbine maintain

its shape. Only few works, mostly

related to prototype testing, on H-

Darrieus turbine were reported in the

literature. Roynarin et al. (Roynarin et

al., 2002) studied theoretically the

power curves for a small prototype of

H-Darrieus turbine and obtained a

maximum Cp of 0.54 at a tip speed ratio

of 2.5. Gupta et al. (Gupta et al., 2010)

experimentally evaluated Cp with tunnel

blockage of a twisted three-bladed

airfoil shaped H-Darrieus turbine madefrom lightweight aluminium blades and

obtained a maximum Cp of 0.15 at H/D

ratio of 1.10. Howell et al. (Howell et

al., 2010) experimentally investigated

the performances of a two-bladed H-

Darrieus turbine and obtained a

maximum Cp of 0.25. Fibreglass

plastics as wind turbine blades would be

popular in near future since it has better

fatigue properties (McGowan et al.,

2002). Further, it is light weighted

having a density of almost 1.9 g/cc,

which is less than aluminium (2.7 g/cc).

In this paper, an attempt has been made

to experimentally study the performance

of a two-bladed H-Darrieus turbine

made from Fibreglass Reinforced

Plastic (FRP). The FRP is anisotropic in

nature unlike aluminium or steel, and it

contains reinforcement of high aspect

ratio (ratio of length to thickness of the

reinforcement) to enhance directional

properties. The physical properties

(Gardiner et al., 2002; Schmit and

Kevin, 1998) of a typical FRP are given

in table 1. The FRP selected for the

present study was a composite of

polyvinyl chloride (PVC) type

thermoplastic, reinforced by fine glass

fibres. The turbine was designed and

fabricated in the department.

Physical Properties Values

Thermal conductivity 0.05 W/mK

Coefficient of thermal

expansion

0.9 1.5 x

10-5

in./in./0F

Density 1.9 g/cc

Tensile strength 148.4 MPa


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Table 1- Physical properties of FRP

Compressive strength101.6 x 10

6

N/m

Modulus of elasticity 1 x 106

psi -

3 x 106

psi

DETAILED DESIGN OF THE

MODEL

The two-bladed H-Darrieus turbine is

shown in Fig 1. The height (H) of the

turbine is 20 cm and width of the blades

is 5 cm with an angular twist of 300

at

the trailing ends as shown in Fig 1. Self-

starting ability of the turbine was

enhanced by the twists at the tips; since

starting torque would be high as

dynamic pressure is also high at the

twist ends. The blades were mounted in

such a way that the twists provided on

the blades were symmetrical. The

blades were mounted on the supports of

mild steel screwed bolts of 5 mm

diameter & 12 cm length, through

which blades were connected to the

central shaft of 1.5 cm diameter. The

blades were moved through the screwed

bolts inwards and outwards to change

the overall turbine diameter (D) andfixed at different locations by nuts.

Changing D, but keeping H constant

created total four H/D ratios. A ball

bearing supported the shaft at the base.

The central shaft, bearing and base were

made from mild steel. The turbine was

tested in an open circuit subsonic wind

tunnel having wind speed adjustable

between 0 to 35 m/sec. The H/D ratios

selected in the study were 0.85, 1.0,

1.54 and 1.72. The turbine rpm was

measured by a digital tachometer

having a least count of 1 rpm, and wind

velocity was measured by a pitot static

tube.

THE WIND TUNNEL

The tests were conducted on an open-

circuit subsonic wind tunnel available in

the department as shown in Fig.2. The

cross-sectional area of test section of the

tunnel was 30 cm x 30 cm. The length of

the test section was 3 meters. The blower

section consisted of a three phase 15 kW

motor having rated rpm of 2890 that

drove the fan. The motor had a starter

for switching on and off the fan. The

operating range of the wind tunnel was

035 m/s. The turbulence intensity was

less than 1%. The brief description of the

wind tunnel is given in (Gupta el al.,

2006).

Fig.1 Two-bladed H-Darrieus turbine


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Fig 2 Schematic diagram of subsonic wind tunnel

ANALYSIS OF RESULTS

The performance of a wind turbine can

be expressed as the variation of power

coefficient (Cp) versus tip speed ratio

(TSR) at any H/D ratio. The wind tunnel

blockage effect was taken into

consideration. When an object is placed

in a wind tunnel, the object creates

blockage to the flow, and it increases the

local free stream wind velocity in the test

section. In wind tunnel testing, its effect

is taken into consideration to determine

the actual power produced by the

turbine. The total factor is the sum of the

velocity increment caused by wake

blockage, solid blockage and also

sidewall blockage (Blackwell et al.,

1977; Pope and Harper, 1966). The total

blockage correction factors for H/D

ratios 0.85, 1.0, 1.54 and 1.72 are

33.35%, 37.53%, 53.17% and 58.59%

respectively. In the present study, the

following relations have been utilized

3

_

2

2

2

1

3

_

2

2

2

1

)(

2

1

)(2

1

blockfree

blockfree

p

V

RVV

AV

RVVA

C

=

=

(1)

Vfree_block= Vfree (1+) (2)

= + + (3)

WH

A

A

A F

TS

F

==

44

(4)

u

uc

q

qq = (5)

Where,

2

S

F

,

,

A

A

4

11

+==

cd

ud

u

c

C

C

q

q (6)

WHncH

AA w

TS

Sw

==

46

46 (7)

11 V

R

V

u == (8)

For the two-bladed H-Darrieus turbine,

the variations of Cp with respect to tip

speed ratio for four H/D ratios: 0.85, 1.0,

1.54 and 1.72 are plotted based on the

experimental observations. The plots of

Cp are shown from Fig.3 to Fig.6. It can

be observed from Fig.3 that, at H/D ratio

of 0.85, Cp increases with the increase of

TSR up to the maximum and then

decreases even though TSR is increased.

The maximum Cp of 0.242 is obtained at

2.124 TSR. At H/D ratio of 1.0, the

variation of Cp follows the same trend as


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Fig. 3 Variation of Cp with TSR for two-bladed H-turbine at H/D = 0.85

Fig.4 Variation of Cp with TSR for two-bladed H-turbine at H/D = 1.0

previous case, which may be observed in

Fig.4. And the maximum Cp of 0.267 is

obtained at 2.214 TSR. Therefore, the

maximum Cp has increased with the

increase of H/D ratio. Figure 5 shows

that at H/D ratio of 1.54, the maximum

Cp of 0.099 is obtained at 0.837 TSR.Now, the maximum Cp has dropped

since the last H/D ratio of 1.0; therefore,

the optimum H/D ratio at which Cp is the

highest is 1.0. At H/D ratio of 1.72,

Fig.6, the maximum Cp is 0.064 at 0.793

TSR. Thus, the highest value of Cp of

0.267 is obtained at H/D ratio of 1.0.

The highest Cp of 0.267 corresponds to a

blockage correction factor of 37.53%,

which is quite high. In spite of high

blockage, the result is quite relevant in

that its Cp is higher than the Cp of H-

Darrieus turbine without blade twist

(Howell et al., 2010). And after scaling

up this turbine, it could be used for

small-scale applications especially in

remote places where grid-connected

electricity is a scarce.

H/D = 0.85

0.2

0.21

0.22

0.23

0.24

0.25

0 0 .5 1 1 .5 2 2 .5

Tip Spee d Rat io

Cp

H/D = 1 .0

0.234

0.243

0.252

0.261

0.27

0 0.5 1 1 .5 2 2.5

Tip Speed Ra tio

Cp


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H/D = 1.54

0.02

0.04

0.06

0.08

0.1

0.12

0 0.3 0.6 0.9 1.2

Tip Speed Rat io

Cp

H/D = 1.72

0.03

0.04

0.05

0.06

0.07

0 0.4 0.8 1.2

Tip Spe ed Ratio

Cp

CONCLUSIONS

Based on the investigation, the

following conclusions have been

drawn:

i) Cp increases with the increase

of H/D ratio up to the maximum

and then decreases even though

H/D ratio is increased. Thus, it can

be concluded that there is an

optimum value of H/D ratio forwhich Cp is the maximum. And

from the present study, the

maximum Cp of 0.267 is obtained

at the optimum H/D ratio of 1.0.

ii) From the present investigation, it is

also seen that the total blockage

correction factor comprising of three

components of solid, wake and sidewall

blockages is quite significant in the

performance measurement of the H-

Darrieus turbine with the highest Cp of

0.267 obtained for 37.53% blockage

correction factor.

iii) It can further be concluded thatblades made from FRP will be a viable

option since it is light in weight, strong

and has significantly high power

coefficient even for high blockage effect,

which is quite comparable to

conventional Savonius like VAWT.


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ACKNOWLEDGEMENTS

The authors acknowledge with

thanks the support provided by Mr.

Sudhir Deb, Mr. Manik

Rajbangshi, Mr. Sashi Mohan Roy

and Mr. Abdul Salam for theirhelp.

NOMENCLATURE

A turbine swept area (HD)

AS blade planform area

(ncH)

c blade chord

Cd,u drag coefficient

uncorrected for

blockage

Cd,c

drag coefficient

corrected for blockage

Cp power coefficient

D overall turbine diameter

H height of turbine

H/

height of test section

n total number of blades

qc dynamic pressure

corrected for blockage

qu dynamic pressure

uncorrected for

blockage

Vfree free-stream windvelocity uncorrected for

blockage

Vfree_block free stream wind

velocity with total

blockage correction

factor

V1 wind velocity on the

upstream of turbine

(m/sec)

V2 wind velocity on the

downstream of turbine

W width of test section solid blockage

correction factor

wake blockagecorrection factor

sidewall blockagecorrection factor

tip speed ratio

(TSR)

w wall correction factor circular frequency of the turbine

total blockage correction factor

REFERENCESDarrieus, G.J.M., 1931. US Patent no. 1

835 018.

Gardiner, C.P., Mathys, Z., Mouritz, A.P.,

2002. Tensile and Compressive Properties

of FRP Composites with Localized Fire

Damage. International Journal of Applied

Composite Materials 9 (6) 353367.

Global Wind Energy Council (GWEC),

2009. Global installed wind power

capacity 2008/2009 Retrieved from

http://www.gwec.net/fileadmin/documents

/PressReleases/PR_2010/Annex%20stats

%20PR%202009.pdf

Gupta, R., Biswas, A., 2010. Performance

measurement of a twisted three-bladed

airfoil-shaped H-rotor, International

Journal of Renewable Energy Technology

1 (3) 279-300.

Gupta, R., Das, R., Sharma, K.K., 2006.

Experimental study of a Savonius-

Darrieus wind machine. In: Proceedings ofthe International Conference on

Renewable Energy for Developing

Countries, University of Columbia,

Washington DC, USA.

Howell, R., Qin ,N., Edwards, J., Durrani, N.,

2010. Wind tunnel and numerical study of a

small vertical axis wind turbine. Renewable

Energy Journal 35 412-422.

Islam, M., Esfahanian, V., Ting, D.S-K.,

Fartaj, A., 2005. Applications of VerticalAxis Wind Turbines for Remote Areas. In:

Proceedings of 5th

Iran National Energy

Conference, Tehran, Iran.

McGowan, J.G., Connors, S.R., 2000.

Wind power: a turn of the century review.

Ann Rev Energy Environ 25 147197.


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Pope, A., Harper, J. J., 1966. Low

Speed Wind Tunnel Testing, JohnWiley & Sons, Inc., New York.

Roynarin, W., Leung, P.S., Datta,

P.K., 2002. The performances of a

vertical Darrieus machine withmodern high lift airfoils. In:

Proceedings of IMAREST

conference MAREC, Newcastle,

U.K.

Savonius, S.J., 1931. The S-rotor

and its applications. Journal of

Mechanical Engineering 53 (5)

333338.

Sheldahl, R.E., Feltz, L.V.,

Blackwell, B.F., 1977. Windtunnel performance data for two-

and three-bucket Savonius rotors.

Journal of Energy 2 160-164.

Schmit, K., 1998. Fiberglass

Reinforced Plastic (FRP) a

comparison to traditional metallic

materials. Retrieved May 29, 1998

from

http://www.fiberbond.com/do

cs/FRPdesign.pdf

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