DOElNASAl3277-4 NASA CR-180812

Performance and Aerodynamic Braking of a Horizontal-Axis Wind Turbine from Small-Scale Wind Tunnel Tests

H.V. Cao and W.H. Wentz, Jr. Wichita State University

July 1987

(BASiL-Ca- 1808 12) PERFOBl¶AOCB AS0 H07-27327 1BBODPBIAfiIIC E B A K I l r G OP A ECBIZCYIAL-AXJS QIHD TIIBEXHIS F R G M SBALL-SCALE uInD TUNNEL TESTS Final Report ( Q i c h i t a State Unir.) Unclas U 3 p Avail: ITIS HC AO3/MF A 0 1 CSCL 10A G3/UU 009C7C6

Prepared for NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Lewis Research Center Under Grant NSG-3277 w?

for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Wind/Ocean Technology Division

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DOE/NASA/3277-4 NASA CR-180812

Performance and Aerodynamic Braking of a Horizontal-Axis Wind Turbine from Small-Scale Wind Tunnel Tests

H.V. Cao and W.H. Wentz, Jr. Wichita State University Wichita Falls, Kansas 67208

Prepared for National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 441 35 Under Grant NSG-3277

for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Wi nd/Ocean Tech nology Division Washington, D.C. 20545 Under Interagency Agreement DE-AI01 -76ET20320

INTRODUCTION

One of the most critical design requirements for large scale horizontal-axis wind turbines i s to provide cost-effective, reliable methods for overspeed control. Overspeed protection is definitely needed when there is a sudden loss of electrical load or in very high wind conditions.

At the present time, large scale horizontal-axis wind turbines utilize partial or full span variable blade pitch to regulate rotor speed. In order to pitch either the full length or a portion of a large wind turbine blade, large blade pitch bearing assemblies and linkages are needed. The design of these systems poses several difficult structural and mechanical problems and adds considerably to system weight and cost (ref. 1).

Alternate methods which require much smaller bearings and pitch actuator systems, and therefore appear t o have potential for reducing rotor costs, are the use of spoilers or ailerons as aerodynamic control devices. Spoilers or ailerons, when deflected, change the lift and drag characteristics of the basic airfoi 1 , producing corresponding changes in rotor torque.

Prior to the present project, spoilers of different sizes and

Due to promising results, these spoilers were later tested on a deflection angles were tested on an NACA 23024 airfoil 2-D model (ref. 2). twenty-inch diameter rotor (ref. 3). the 20 percent chord spoiler at 90 degrees angle o f deflection and with hingeline position located at 10 percent chordline on the upper surface of the airfoil produced negative torque for all tip-speed ratios greater than or equal to 0.78. However, since the blade structure is typically located primarily in the furward 50 percent of the airfoil section, it is difficult to design a spoiler system for this hingeline position without a

The results of these tests show that

1

significant reduction in strength, or alternatively, a substational increase in weight.

Ailerons have also been evaluated as aerodynamic control devices. The primary reason for the preference of ailerons over spoilers is that the entire moveable surface is located on the aft 50 percent of the airfoil making it possible to carry the main rotor structure (main spar) uninterrupted from hub to tip. Furthermore, ailerons, unlike spoilers, have the capability of providing both positive and negative increments in lift. The lift coefficient can be increased by deflecting the aileron upward. Upward aileron deflection will cause the lift to decrease which, in turn, reduces torque. Studies of predicted rotor performance based on wind tunnel tests of ailerons on a 3-D reflection plane model (ref. 4) indicates a strong possibility of slowing the rotor down to a very low tip-speed ratio. present project is to evaluate the performance of the vented aileron/ deflector combination in a test which includes 3-D induced effects and possible spanwise boundary layer effects.

This simplifies and lightens the structure.

The purpose of the

Earlier studies (ref. 4) have shown that a plain (unvented) aileron with or without lower surface deflector was adequate for power modulation, but inadequate for full aerodynamic braking. These studies also revealed discrepancies between analysis of rotor performance from 2-D wind tunnel data and actual rotor performance. The conclusions from the earlier research are as follows: (1) Aileron control is structurally and mechanically feasible; (2) the ailerons tested were adequate for power modulation, but marginal for aerodynamic braking; nd (3) rotor analysis codes are questionable for predicting effectiveness of aerodynamic braking devices, at least f o r one case. Thus, even though airfoil section tests and analysis indicate that the vented aileron deflector is adequate, rotating tests are essential for verification. Small scale wind tunnel tests have Reynolds number and model detail limitations, yet they are relatively low-cost, quick, and provide data of high quality in a

2

controlled environment. planned.

It is on this basis that the present tests were

For this project a twenty-inch diameter untapered, untwisted, and unpitched rotor equipped with an aileron over the outboard 30 percent span was tested. aileron deflection opens a gap between the aileron and the airfoil. Aileron chord was 30 percent, and a lower 20 percent chord solid extension plate was used to extend the lower surface of the aileron. This configuration was developed in airfoil wind tunnel tests conducted earlier (ref. 4). The purpose of the special hingeline position and the extension plate is to force air to flow upward through the gap at high angles of attack. chordwise suction force.

The hingeline position was designed such that an upward

This upward flow causes the lift to decrease, thus reducing

Performance characteristics of an NACA 23024 rotor and an NACA 643-621 rotor without ailerons were also studied both experimentally and analytically. Analytical results were obtained by using the wind turbine performance computer program WIND-I1 (ref. 5). studies i s to correlate rotor performance prediction from 2-D data with rotating experiments.

One purpose of the present

Surface flow patterns were studied using fluorescent mini-tufts attached to the suction side of the rotor. was to determine the extent and nature of spanwise flow along the rotor at high angles of attack.

The purpose of the flow study

This report is an extension of a master o f science thesis by the first author (ref. 6). additional analytical calculations from WIND-I1 not reported earlier.

The report includes transition strip results and

3

L I S T OF SYPISOLS

a

A C

cD

cL cN cS cP cT

Mt

9 M

P

q

Q r R

ReW

Ret r Pm T

TS

TSR

vR

vT

vW a

6a U

P

R

4

Wind r e t a r d a t i o n ( i n d u c t i o n ) f a c t o r

Area swept by r o t o r d isk, f t

B1 ade chord, f t

C o e f f i c i e n t o f drag

C o e f f i c i e n t o f l i f t

C o e f f i c i e n t o f normal f o r c e

C o e f f i c i e n t o f suc t i on

C o e f f i c i e n t o f power, P/(qAVW)

C o e f f i c i e n t o f t h r u s t , T I (qA)

G r a v i t a t i o n a l accelerat ion, 32.2 f t / s e c

Freestream Mach number

T i p Mach number

Power, W

Tunnel dynamic pressure, p s f

Torque, 1 b - f t

Radial l o c a t i o n along blade, i n

Blade t i p rad ius, i n

Freestream Reynolds number per u n i t length, pVw/u

Ro ta t i ona l speed i n r e v o l u t i o n s per minute

Thrust, l b

T r a n s i t i o n S t r i p s , each 0.005" t h i c k x 0.10" wide

Tip-speed r a t i o , V T / V w

Resul tant v e l o c i t y , f t / s

Blade t i p v e l o c i t y , R, f t / s

Freestreani wind v e l o c i t y , f t / s

Angle of a t tack, deg

Angle of a i l e r o n d e f l e c t i o n (nega t i ve upward), deg

A i r densi ty, s l u g s / f t

Angular v e l o c i t y , r a d / s

2

2

T i p chord Reynolds number, R E W ( c ) ( l + TSR 2 ) 1 / 2

C o e f f i c i e n t o f dynamic v i s c o s i t y , l b f - s e c / f t 2 3

.

BACKGROUND

The performance o f a ho r i zon ta l a x i s wind t u r b i n e can be analyzed

from the a c t i o n of t h e aerodynamic forces on t h e t u r b i n e blade. The b lade

i s analyzed u s i n g chordwise s t r i p s along t h e span so t h a t t he

two-dimensional ana lys i s can be used on each element. Overa l l b lade

fo rces and moments are obtained by summing element c o n t r i b u t i o n s .

1 shows a system of forces ac t ing on a wind t u r b i n e blade element.

combination o f t h e wind ve loc i t y , VN, the i n d u c t i o n f a c t o r , a, and t h e

e lement 's v e l o c i t y caused by blade r o t a t i o n , R r, forms an e f f e c t i v e o r a

r e s u l t a n t wind v e l o c i t y , VR. This r e s u l t a n t wind v e l o c i t y causes l i f t

and drag forces on t h e blade element.

u t i l i z e blades w i t h zero p i t c h and zero t w i s t .

torque, Q ( p o s i t i v e i n the d i r e c t i o n o f r o t a t i o n ) i s produced o n l y by t h e

f o r c e component i n t h e d i r e c t i o n p a r a l l e l t o the a i r f o i l chord l ine , w h i l e

t h e t h r u s t , T, ( p o s i t i v e i n the downstream d i r e c t i o n ) i s produced o n l y by

t h e f o r c e component i n the d i r e c t i o n normal t o the a i r f o i l chord l ine . I n

nondimensional forms, t h e torque-producing component i s c a l l e d chordwise

suc t i on c o e f f i c i e n t , C and the th rus t -p roduc ing component i s c a l l e d

norriial c o e f f i c i e n t C The component C i s taken p o s i t i v e i n the

d i r e c t i o n toward t h e leading edge o f t he a i r f o i l so t h a t p o s i t i v e C

produces p o s i t i v e power. The coiiiponent C N i s def ined p o s i t i v e i n the

p o s i t i v e t h r u s t (downwind) d i rec t i on . The mathematical r e l a t i o n s h i p s

between these components arid l i f t and drag c o e f f i c i e n t s are:

F i g u r e

The

Many l a r g e sca le wind tu rb ines

For these blades, t he

S'

N ' s S

Cs = C L s i n ( a ) - C 0 cos ( u ) (1)

cN C L cos ( u ) + C I) sin ( a )

D where C i s the t r a d i t i o n a l a i r f o i l sec t i ona l l i f t c o e f f i c i e n t and C

i s the t r a d i t i o n a l sec t i ona l drag c o e f f i c i e n t . The e f f e c t i v e angle o f

a t tack , (1, i s formed by the resu l tan t w i n d v e l o c i t y and the a i r f o i l

c h o r d l i n e (which i s i n the plane o f r o t a t i o n f o r t he case o f a ze ro - tw is t

L

5

and zero-pitch wind turbine blade). Since the local taiigential velocity decreases with decreasing radius along the span, the angle of attack is higher for inboard blade stations. ratio and local blade radius on the local angle of attack. For a normal operating tip-speed ratio of about 5, the angles of attack range from approximately 12 t o 20 degrees for the outer 50 percent portion of the blade.

Figure 2 shows the effects of tip-speed

The purpose of the present project is to reduce the rotational speed of the wind turbine under no-load conditions. Studies ha;re shown that for tip-speed ratios of about 7.0 or less, a small mechanical brake could be utilized to bring the rotor to a complete stop. At this tip-speed ratio, the range of angles of attack is from 60 to 90 degrees for all stations along the blade span. Therefore, studies of airfoil characteristics at very high angles of attack are essential for slow-down analysis of wind turbines.

FACILITY AND INSTRUMENTATION

All tests were conducted in the 7 x 10 foot Walter Beech Memorial Wind Tunnel at Wichita State University, with the test assembly installed as shown in figure 3. Instrumentation consisted of a special force-moment balance in which a 10 hp variable-speed, water-cooled, variable-frequency model motor was mounted. This force balance i s fitted with strain-gaged flexures so that torque and thrust can be measured directly. The motor speed can be controlled by means of a variable frequency external excitation system. internally. Hewlett-Packard Model 21MX iiiini-coiiiputer located in the tunnel control rooin. solid blockage and wake blockage as given in reference 7. rotor disk area to tunnel cross-section area is only 0.0321, making solid and wake blockage corrections sinall. Traditional wind turbine performance

Rotor speed wds measured by a signal generator mounted Force data acquisition arid processing were accomplished by a

These force data were corrected using wind tunnel corrections for The ratio of

6

.

parameters were c a l c u l a t e d us ing a da ta r e d u c t i o n computer program

a v a i l a b l e i n t h e WSU Walter Beech Wind Tunnel.

recorded, tabu la ted and p l o t t e d .

These q u a n t i t i e s were then

Surface f low pa t te rns were observed us ing f l u o r e s c e n t m i n i - t u f t s

a t tached t o t h e s u c t i o n (downwind) s i d e o f t he rotor-blade, w i t h

i l l u m i n a t i o n prov ided by a 400 watt-second s t u d i o s t robe l i g h t w i th a

UV-passing f i l t e r (Corning Glass no. 5970).

photographed by a motorized, remote-control Pentax LX camera f i t t e d w i t h a

200 nim l ens and a Wratten 2B f i l t e r ; t h e camera was f i x s d t o a spec ia l

t r i p o d l oca ted about 10 r o t o r diameters downstream.

Flow p a t t e r n s were then

MODEL D E S C R I P T I O N

F igu re 4 shows t h e geometry of t he r o t o r models. Three r o t o r models

were used i n these t e s t s . A l l three r o t o r s have t h e p lanform shown i n

f i g u r e 4(a) , w i t h diameters o f 20 inches and chords o f 1.75 inches.

models have a i r f o i l sect ions f o r a l l s t a t i o n s f rom 21 percent span t o t h e

t i p . The hub sec t i ons are rectangular w i t h rounded edges o u t t o 10 percent span, w i t h a tapered t r a n s i t i o n t o t h e a i r f o i l s e c t i o n a t 21

percent span.

o f these r o t o r s i s 0.111.

These

The s o l i d i t y f a c t o r (b lade p lanform area/swept d i s k area)

The f i r s t model uses the NACA 23024 a i r f o i l ( f i g . 4 ( b ) ) and t h e

second model uses t h e NACA 643-621 a i r f o i l ( f i g . 4 ( c ) ) f o r s t a t i o n s f rom

21 percent t o t h e t i p . The th i rd model u t i l i z e s t h e NACA 23024 a i r f o i l ,

mod i f i ed t o i nco rpo ra te a 30 percent chord a i l e r o n a t -90 degree f i x e d

d e f l e c t i o n f rom 70 percent span t o t he t i p .

s e c t i o n i s shown i n f i g u r e 4 ( d ) . The h i n g e l i n e p o s i t i o n o f t he a i l e r o n i s

a t 80 percent along the chord f r o m t h e l ead ing edge and 14 percent above

t h e a i r f o i l cho rd l i ne .

h i g h pressure s i d e o f the a i l e r o n extending forward f o r a dis tance equal

t o 20 percent of t h e a i r f o i l chord.

The geometry o f t h i s a i l e r o n

An extension p l a t e or d e f l e c t o r i s at tached t o t h e

Coordinates f o r t h e NACA 23024 a i r f o i l

7

and the NACA 643-621 airfoil (ref. 8) are given in the Appendix.

The ai leron/deflector geometry and hinge1 ine location were determined from airfoil section tests documented in reference 4. The vented deflector aileron presented a special challenge for model fabrication because of the high centrifugal loading (7000 g's) associated with operation at 5000 rpm. cutting froin the basic planform). graphite composite laminate, and the aileron/deflector assembly was attached to the rotor by a series of graphite fibers looped to form a tension "belt" which was bonded into the main blade to carry the centrifugal forces.

The aileron was fabricated from solid maple (the section removed by The deflector was fabricated from a

RESULTS AND DISCUSSION

For most tests reported here, rotor speed was kept constant and tunnel dynamic pressure was varied. 5,500 rprn and the tunnel dynamic pressure was varied from 1 to as much as 50 psf. The purpose of testing at high tunnel dynamic pressure and low rpm was to obtain very low tip-speed ratios. numbers and tip-speed Mach numbers are given in Table 1. presented in terms of thrust and power coefficients as a function of tip-speed ratio (TSR), and rotor power output as a function of wind speed.

The rotor speeds ranged from 600 to

Test tip-speed Reynolds Results are

Analytical studies were conducted for most of the configurations tested using WIND-11, a FORTRAN code for predicting rotor performance (ref. 5). One of the input requirements for WIND-I1 is a s e t of 2-D lift and drag coefficient data as functions of angle o f attack for the airfoil section on the rotor. It is important to note that all 2-D data used as inputs to WIND-I1 were from tests of a 9-inch chord, 36-inch span model which were obtained at the Reynolds number of 0.6 x 10 9). Chord Reynolds numbers for the present tests were lower, ranging from 0.02 x 10 at the inboard station to 0.11 x 10 at the tip, for low

6 (refs. 2 and

6 6

rpm tests. from 0.11 x 10 at the inboard station to 0.58 x 10 at the tip.

For the highest rprn tests, the chord Reynolds numbers ranged 6 6

Tests of the Clean NACA 23024 Rotor Without Ailerons

Figures 5 and 6 present the results of testing the NACA 23024 rotor without the ailerons and without transition strips (clean). aerodynamic characteristics of airfoils at low Reynolds numbers are often dominated by laminar separation, transition location effects were studied analytically using 2-D data with 1, 2 and 3 transition strips (from ref. 4) as inputs to WIND-11. experimental measurements as shown in Figure 5.

Since the

Results of these studies are compared to

Figure 5 shows a plot of thrust coefficient as a function of TSR for the clean NACA 23024 rotor. coefficient o f this rotor increases with TSR. Theoretical calculations show that the case with no transition strip shows the best agreement with the experimental measurements, although all cases show about the same trend.

As predicted by WIND-11, the thrust

The effects of transition strips are much more significant on power coefficient than thrust coefficient. Figure 5(b) shows a plot of power coefficient as a function of tip-speed ratio. Experimental data shows that the rotor state of zero-power occurred at the TSRs of 1.5, 4.0 and 8.0. Maximum power coefficient occurred at TSR of about 5.0. calculations with no transition strip show a somewhat higher Cp peak than experimental results. Transition strips reduce maximum predicted

C,,. The analysis based on 2-D data with one transition strip produces about the same maximum power coefficient as the clean rotor tests.

Theoretical

Power calculated and plotted as a function of figures 6(a) through (c) for rotor speeds of 2000, respectively. For all three cases, theoretical ca

wind speed is shown in 3000 and 4000 rpm, culations from WIND-I1

9

over-predicted the peak power and the cut-out wind speed for the rotor. The analysis, however, agrees very well with the experimental measurements for the portion of the power curve from the point of cut-in velocity to the point where experimental data shows maximum power is reached (blade section stall ing).

One reason WIND-I1 predictions may differ from the rotor experiments is that the airfoil section data used as a input to WIND-I1 were from tests at a Reynolds number of 0.6 x lo6, while rotor Reynolds numbers were substantially lower. It is recommended, therefore, that tests be conducted to obtain low Reynolds number airfoil data for these blade sections. The lower Reynolds number airfoil section data should then be used as inputs to WIND-I1 to refine the predicted performance of the rotor blade. The Mach number differences between non-rotating and rotating experiments are not considered significant.

Tests of the Clean NACA 64,-621 Rotor "

The test results of the NACA 643-621 rotor without transition strips are presented in terms of nondimensional parameters as shown in figure 7 and rotor power output as shown in figure 8.

As shown in figure 7(a), theoretical calculations are similar to experimental measurements for thrust coefficient as a function of TSR. figure 7(b) the tests show a somewhat higher maximum power coefficient, but in general the agreement is very good. these tests is that the NACA 643-621 rotor had only one speed (TSR of 6.7) for which power is zero, while the theoretical calculations from WIND-I1 predict states of zero-power for the rotor to occur at TSRs of 0.4, 2.0 and 6.7.

In

A very interesting point for

Figure 8 presents the results for the NACA 643-621 rotcjr in terms of power as a function of wind speed. Similar to the results for the NACA

23024 r o t o r , a n a l y t i c a l ca l cu la t i ons over -pred ic t t h e peak-power, and

agree w i t h exper imental measurements o n l y f rom t h e p o i n t o f c u t - i n

v e l o c i t y t o t h e p o i n t o f maximum power measured exper imenta l ly . As wind

v e l o c i t y i s increased, however, r e s u l t s f rom t h i s s e r i e s o f t e s t s a re no

longer s i m i l a r t o those of t h e NACA 23024 r o t o r .

f rom W I N D - I 1 f a i l t o p r e d i c t the cut-out wind speed o f t h e NACA 643-621

r o t o r . F igu re 8 (a ) shows the p l o t of power as a f u n c t i o n o f wind speed

f o r t h e NACA 643-621 r o t o r a t 2000 rpm.

r o t o r power ou tpu t reaches i t s maximum a t t h e wind speed o f about 13 m/s.

For wind speeds g rea te r than 13 m/s, power decreased.

cut -out wind speed f o r t h i s case a t 26 m/s.

p red ic t i ons , t h e power ou tpu t of t he NACA 643-614 r o t o r remains n e a r l y

cons tan t a t p o s i t i v e power f o r wind speed f rom 25 t o 29 m/s. Due t o t h e

overspeed l i m i t a t i o n on the wind tunnel motor-dynamometer system, maximum

wind speed o f t h e t e s t s was r e s t r i c t e d t o 29 m/s.

v e l o c i t y was l i m i t e d t o o n l y 24 m/s f o r t h e r o t o r a t 3000 rprn, s i m i l a r

r e s u l t s were obta ined as shown i n F igu re 8(b) .

Furthermore, c a l c u l a t i o n s

Experimental da ta show t h a t t h e

WINE-I1 p r e d i c t e d a

Un l i ke t h e o r e t i c a l

Although tunnel

I n summary, t h e WIND-I1 p red ic t i ons f o r t h e NACA 643-621 r o t o r ,

based on a i r f o i l sec t i on data, are reasonable f o r low angles o f a t tack ,

b u t poor f o r h i g h angles o f a t tack ( h i g h wind speed). The present t e s t

da ta are charac ter ized by a d i s t i n c t peak i n t h e power versus wind speed

p l o t , f o l l owed by a r e g i o n o f decreasing power, and then a r e g i o n i n which

power i s r e l a t i v e l y constant w i t h wind speed.

2000 rpm, t h e measured power a t h igh wind speed exceeds t n e WIND- I1

p r e d i c t i o n .

t e s t s , w i th power i n i t i a l l y decreasing beyond peak power, f o l l owed by

cons tan t o r i nc reas ing power as wind speed i s f u r t h e r increased. He

descr ibes "adjustments" t o be made t o t h e a i r f o i l sec t i on da ta t o match

measured power f o r t he h igh wind speed cond i t ions . NASA Lewis Research

Center t e s t r e s u l t s ( r e f . 12) f r o m a large-scale MOD-OA wind t u r b i n e show

t h a t t h e power a l s o exceeded W I N D - I 1 p r e d i c t i o n s a t h igh wind speeds.

t h e MOD-OA r o t o r , t he power reached a maximum, and then remained cons tan t

I n f a c t , f o r t h e case o f

Rasmussen ( r e f . 11) repor ted r e s u l t s s i m i l a r t o t h e present

For

11

f o r h ighe r wind speeds.

the NACA 643-621 r o t o r are q u i t e s i m i l a r t o t h e Rasmussen r e s u l t s , and

somewhat s i m i l a r t o the NASA MOD-OA r e s u l t s .

The t rends from t h e present wind tunnel t e s t s of

Performance Comparison Between t h e Two Rotor Models

F igures 9 and 10 compare t h e t e s t r e s u l t s between t h e 23024 r o t o r and

the 643-621 r o t o r .

c h a r a c t e r i s t i c s f o r bo th r o t o r s .

r o t o r i s n e a r l y t h e same as t h a t of t he NACA 23024 r o t o r , b u t i t occurs a t

a lower TSR.

Cp f o r TSR less than about 5 b u t lower Cp f o r TSR g rea te r than about

5.

power, and a t h igh wind, t he 643-621 r o t o r produces g rea te r power.

t he th ree rpm s e t t i n g s tested, the 643-621 r o t o r produces h ighe r maximum

power than t h e 23024 r o t o r ( f i g . 10) .

E f f e c t s o f T r a n s i t i o n S t r iDs on the Two Rotors

Table 2 summarizes some o f t h e performance

The riiaximum Cp f o r t he NACA 643-614

As shown i n f i g u r e 9(b), t h e 643-621 r o t o r produces h ighe r

This means t h a t a t lower wind speed, t h e 23024 r o t o r produces g r e a t e r

For

The purpose f o r t h i s t e s t s e r i e s was t o ev l u a t e the e f f e c t s o f

t r a n s i t i o n s t r i p s on r o t o r performance.

commercial d r a f t i n g c h a r t tape.

t o apply c o n s i s t e n t l y .

span a t 5 percent chord on the upper su r face and a t 10 percent chord on

the lower surface o f t h e r o t o r . Tests were conducted on bo th r o t o r s w i t h

0, 1, 2 and 3 t r a n s i t i o n s t r i p s ( th icknesses O.O", 0.005", 0.010" and

0.015"). The tape thicknesses are l a r g e r e l a t i v e t o r o t o r th ickness, b u t

are d i c t a t e d by t h e low Reynolds number o f t h e t e s t s .

a t t h e t i p f o r these t e s t cond i t i ons i s 0 . 3 ~ 1 0 .

The t r a n s i t i o n s t r i p s were

This tape i s r e a d i l y a v a i l a b l e and easy

The tape s t r i p s were at tached along t h e e n t i r e

The Reynolds number 6

F igu re 11 presents t h e r e s u l t s o f t e s t i n g t h e NACA 23024 r o t o r w i t h

0, 1, 2 and 3 t r a n s i t i o n s t r i p s . I t i s shown i n these f i gu res t h a t

t r a n s i t i o n s t r i p s r e s u l t i n small reduc t i ons i n t h r u s t c o e f f i c i e n t b u t

l a r g e p e n a l i t i e s i n power c o e f f i c i e n t .

i n s t a l l e d , t h e NACA 23024 r o t o r produced negat ive power f o r a l l t ip-speed

r a t i o s .

t h e degradat ion i n power coe f f i c i en t f o r one and two t r i p s t r i p s , b u t

underpredic ts t h e power l o s s caused by t h e t h i r d t r i p s t r i p .

With th ree t r a n s i t i o n s t r i p s

As shown i n f i g u r e l l ( c ) , t h e WIND- I1 program accu ra te l y p r e d i c t s

The r e s u l t s o f t e s t i n g the t r a n s i t i o n s t r i p s on t h e NACA 643-621

r o t o r are shown i n f i g u r e 12. small r e d u c t i o n i n t h r u s t c o e f f i c i e n t ( f i g . 12 (a ) ) and a l s o r e l a t i v e l y

smal l changes i n power c o e f f i c i e n t ( f i g . 12(b)) .

12 (c ) , t he W I N D - I 1 program c o r r e c t l y p r e d i c t e d a smal l e f f e c t o f t r a n s i t i o n

s t r i p s on t h e power c o e f f i c i e n t of t h i s a i r f o i l and again underpredicted

t h e power l o s s f rom t h e t h i r d t r a n s i t i o n s t r i p .

For t h i s r o t o r , t r a n s i t i o n s t r i p s cause a

As shown i n f i g u r e

With t h r e e t r a n s i t i o n s t r i p s i n s t a l l e d , r o t o r peak power i s reduced

from 0.21 kW t o about 0.15 kW as shown i n f i g u r e 12(d).

t r a n s i t i o n s t r i p s i n s t a l l e d , however, r o t o r peak power i s increased from

0.21 kW t o about 0.23 kW.

behavior i s t h a t t h e NACA 643-6Zl r o t o r had laminar separat ion on t h e

upper sur face f o r t h e low Reynolds number tested, and a t r i p c o n s i s t i n g of

1 o r 2 t r a n s i t i o n s t r i p s helped prevent t h i s separat ion.

were repo r ted by Rasmussen ( r e f . 11) who showed t h a t t r a n s i t i o n s t r i p s

penal ized peak power a t h i g h rpm ( h i g h Reynolds number), b u t increased

peak power a t low rpm ( low Reynolds number).

r o t o r w i th NACA 63-212/24 a i r f o i l sect ions.

With 1 o r 2

The probable reason f o r this unexpected

S i m i l a r t rends

His t e s t s were on a t w i s t e d

The most s i g n i f i c a n t f i nd ings from t h i s s e r i e s o f t e s t s i s t h a t

t r a n s i t i o n s t r i p s have a much la rge r p e n a l t y on t h e NACA 23024 r o t o r than

on t h e NACA 643-631 r o t o r . s e n s i t i v e t o roughness than the NACA 643-621 a i r f o i l .

were obta ined from 2-D t e s t s of t h e 23024 a i r f o i l and t h e 643-618

a i r f o i l a t Reynolds number of O.6x1O6, documented i n WSU Report WER-16

( r e f . 13).

That i s , t h e NACA 23024 a i r f o i l i s much more

S i m i l a r t rends

13

Flow Visualization

A series of flow visualizations were conducted on the clean NACA 23024 rotor and the NACA 643-621 rotor. Surface flow patterns were observed using fluorescent mini-tufts attached to the upper surface (suction side) from 30 to 90 percent rotor radius at 10 percent increments along the blade span, with illumination provided by an ultra-violet strobe light. The tests were conducted at 800 rpm, with tunnel dynamic pressure varied from 0 psf (infinite TSR) to 5 psf (TSR about 1).

The purpose of these tests, as stated earlier, was to determine the extent of spanwise flow along the blade. attack near stall, spanwise flow helps delay separation on the upper surface of the rotor, resulting in power prediction discrepancies discussed in preceding sections.

It is believed that at angles of

Figure 13 shows typical results of the flow visualization tests. Figure 13(a) shows the picture of the clean NACA 643621 rotor at infinite tip-speed r a t i o ( 0 psf tunnel dynamic pressure). the tufts indicate only chordwise flow for all stations along the blade surface. This tuft orientation indicates that the tuft g-load or centrifugal acceleration does not have a major effect on the tufts. When the tip-speed ratio was decreased by increasing the tunnel wind velocity, spanwise flow began to develop, starting from the inboard stations. This was shown by the increasing number of tufts which turned from their original chordwise positions to point radially outward.

The patterns of

Table 3 summarizes the results for this series of flow visualization tests. U3-6Zl rotor to encounter spanwise flow at lower TSR than the 23024 rotor seems inconsistent with the power measurements which show more positive power for the 643-621 rotor. data for the two airfoils reveals that while the 643-621 airfoil has a

If spanwise flow is evidence of blade stalling, the trend of the

Careful study o f airfoil section

lower initial stalling angle, the stall progression is quite slow, and the CL curve is quite flat near the peak. to retain high lift even when substantial separation is present.

Thus, this airfoil has the ability

Tests of the NACA 23024 Rotor with 30 Percent Chord Aileron

Figures 14 and 15 present the results of testing the NACA 23024 rotor equipped with a vented aileron/def lector locked in the 90' degree upward posit ion.

Figure 14 shows the comparison between the theoretical predictions from WIND-I1 and the experimental measurements for the gap-open aileron configuration. WIND-I1 predicts approximately 10 percent lower thrust coefficients for nearly all tip-speed ratios greater than 2 as shown in figure 14(a). of tip-speed ratio. same results as those of the experimental measurements.

Figure 14(b) shows a plot of power coefficient as a function Calculations from WIND-I1 show almost exactly the

It is shown in figure 15(a) that by leaving the gap between the airfoil and the aileron open, the thrust coefficient is somewhat lower than that of the basic NACA 23024 rotor for TSR from 4 to about 8. When the gap is closed, thrust coefficients become higher than those of the basic rotor and the gap-open aileron configurations, for TSR from 1 to about 5. gap-closed aileron configuration has larger profile drag area than the basic rotor and the gap-open aileron rotor configurations. than 5 (at low tip angles of attack), however, thrust coefficients become lower due to the loss of lift caused by the upward deflection of the aileron.

At this range of TSR (at high tip angles of attack), the

At TSR greater

Figure 15(b) shows the effects of the aileron on the power coefficient, as a function of TSR.

produced negative torque for all TSRs. Both gap-open and gap-closed ailerons

Due to test limitations, the

15

lowest achievable TSR f o r t he gap-open c o n f i g u r a t i o n was 0.65 and a TSR of

0.54 f o r t h e gap-closed con f igu ra t i on . The gap-open a i l e r o n c o n f i g u r a t i o n

produced somewhat l a r g e r negat ive torque c o e f f i c i e n t s than the gap-closed

c o n f i g u r a t i o n f o r a l l TSRs tes ted (up t o about 8).

I n order t o determine the s t a t e o f zero-torque f o r t h i s model, t h e

r o t o r was windmil led; t h a t i s , t he r o t o r was d r i v e n o n l y by t h e tunnel

wind v e l o c i t y , f o r a s e r i e s o f tunnel dynamic pressures.

zero-torque s ta te f o r t he gap-open c o n f i g u r a t i o n was found t o be -0.6, and

-0.7 f o r t h e gap-closed con f igu ra t i on .

r o t o r was t u r n i n g backward.

The TSR f o r t h e

A nega t i ve TSR means t h a t t h e

I n addi t ion, a coast-down t e s t was conducted f o r the gap-open a i l e r o n

c o n f i g u r a t i o n . For the t e s t , t he tunnel dynamic pressure was kep t a t 9

psf , and t h e r o t o r speed was d r i v e n t o 3000 rpm, which corresponds t o a t ip-speed r a t i o n o f about 5.

then disconnected, and t h e r o t o r blade was a l lowed t o coast down t o an

e q u i l i b r i u m zero-torque s ta te .

r o t o r t o decelerate f r o m 3000 rpm t o zero rpm and about 2 more seconds t o

reach t h e reve rse - ro ta t i on e q u i l i b r i u m s t a t e o f zero-torque a t t h e

t ip-speed r a t i o o f -0.6.

a b i l i t y o f t h i s c o n f i g u r a t i o n t o p r o t e c t aga ins t r o t o r overspeed.

The e l e c t r i c a l power d r i v i n g t h e r o t o r was

It took approximately f i v e seconds f o r t he

Thus these t e s t s have c l e a r l y demonstrated t h e

The f a c t t h a t t he a i l e r o n - c o n t r o l l e d r o t o r r e s u l t s i n reverse

r o t a t i o n i s not an insurmountable problem. Three s o l u t i o n s are poss ib le :

(1) Al low t h e slow reverse auto-rotat ion. This r a t e i s so low t h a t

i t probably would n o t r e s u l t i n damage, even i n hu r r i cane winds.

( 2 ) L i m i t a i l e r o n d e f l e c t i o n angle t o l e s s than 90 degrees.

( 3 ) Reduce t h e s i z e o f t h e a i l e r o n chord o r lower sur face extens ion

p la te .

It is recommended that an aileron of this type be tested at smaller angles of deflection (60°, 70' or 80') or with smaller extension plates (5, 10 or 15 percent chord) on the lower surface.

1.

2.

3.

4.

5.

1.

CONCLUSIONS

The NACA 643-621 rotor produces higher peak power than the NACA

23024 rotor for a given rotor speed. The NACA 23024, however, gives more power than the NACA 643-621 at low wind speeds.

Transition strip studies show that the NACA 23024 rotor is very sensitive to roughness and that when transition strips are installed, it suffers a greater penalty than the NACA 643-621 rotor.

Surface tuft studies indicate the existence of spanwise flow for a TSR less than or equal to about 1 for the NACA 23024 rotor and less than or equal about 3 for the NACA 643-621 rotor.

Analytical studies from WIND-I1 consistently overpredicted maximum power for the two clean rotor configurations. however, show very good correlation with test results for operation at low wind speeds (high TSR).

The predictions,

For the purpose of loss-of-load control, the aileron configuration tested for this project i s capable of producing more than enough negative torque to prevent overspeed. aileron will rotate backward at a tip-speed ratio of -0.6.

The unloaded rotor with

RECOMMENDATIONS

Tests should be conducted to obtain low Reynolds number airfoil data for these blade sections, and these data should be used to check the analytical model.

1 7

2. The vented a i l e r o n / d e f l e c t o r c o n f i g u r a t i o n t e s t e d i n t h i s p r o j e c t

should be evaluated on a f u l l - s c a l e wind t u r b i n e machine where much

h ighe r Reynolds numbers e x i s t .

3. The a i l e r o n o f t h i s type should be t e s t e d a t smal ler angles o f

d e f l e c t i o n (70' and 80') o r w i t h smal ler extens ion p l a t e s (5, 10

and 15 percent chord) on t h e lower sur face t o reduce Pegat ive

r o t a t i o n r a t e .

REFERENCES

1. Wentz, W. H.; Snyder, M. H.; and Calhoun, J. T.: " F e a s i b i l i t y Study

o f A i l e r o n and S p o i l e r Contro l Systems f o r Large Hor i zon ta l Ax i s Wind

Turbines," NASA CR-159856, DOE/NASA/3277-1, WER-10, NASA Lewis

Research Center, 1980.

2 . Wentz, W. H.; Snyder, M. H.; and Cao, H. V . : " E f f e c t s o f S p o i l e r

Hinge1 ine Locat ion on t h e NACA 23024 A i r f o i l ,I' (Unpublished I n t e r i m

Report) WER-27, Wind Energy Laboratory, W ich i ta S ta te U n i v e r s i t y ,

1984.

3. Tra iner , A. G.: "Overspeed Contro l o f Hor i zon ta l Ax is Wind Turbines

Using Spoilers," M. S. Thesis, W ich i ta S ta te U n i v e r s i t y , 1984.

4. Snyder, M. H.; Wentz, W. H.; and Cao, H. V.: "Add i t i ona l R e f l e c t i o n

Plane Tests o f Contro l Devices on an NACA 23024 A i r f o i l , "

(Unpublished I n t e r i m Report) WER-26, Center f o r Energy Studies,

W ich i ta State U n i v e r s i t y , 1985.

5. Snyder, M. H., and Staples, D. L.: "WIND- I1 Users Manual,"

(Unpublished I n t e r i m Report) WER-15, Wind Energy Laboratory, W ich i ta

S ta te Un ive rs i t y , 1982.

6. Cao, H. V.: "Performance and Aerodynamic Brak ing o f a Hor i zon ta l -

Ax is Wind Turb ine f rom Small-scale Wind Tunnel Tests," Master o f

Science Thesis, Wich i ta State Un ive rs i t y , 1985.

7. Pope, A., and Harper, J. J.: Wi ley and Sons, Inc., New York, 1966.

Low Speed Wind Tunnel Test ing, John

8. Abbott, I. H., and Van Doenhoff, A. E.: Theory o f Wing Sect ions,

Dover Pub l ica t ions , 1958.

9. Staples, D. L., and Wentz, W. H.: " A n a l y t i c a l Studies o f Aerodynamic

Brak ing and Contro l o f the Mod-0 Wind Turb ine wi th a 38 Percent Chord

Vented A i l e r o n on an NACA 643-621 T i p Section," (Unpublished

I n t e r i m Repor t ) PIP-13, Wichi ta S ta te Un ive rs i t y , 1985.

10. Wentz, W. H.; Ostowari, C.; Manor, D.; and Snyder, M. H.:

"Hor izon ta l Ax is Wind Turbine Wake and Blade Flow Measurements f rom

Model Tests," (Unpublished I n t e r i m Repor t ) WER-24, Wind Energy

Laboratory, W ich i ta S t a t e University, i984.

11. Rasmussen, F.: "Aerodynamic Performance o f a New LM 17.2 m Rotor,"

Twe l f t h Meet ing o f Experts - Aerodynamic Ca lcu la t i ona l Methods f o r

WECS, IEA, Copenhagen, 1984.

12. V i terna, L. A., and Janetzke, D. C.: "Theore t ica l and Exper imental

Power from a Large Horizontal-Axis Wind Turbine," NASA TM 82944, 1982.

13. Snyder, M. H.; Wentz, W . H.; and Ahmed, A.: "Two-Dimensional Tests

o f Four A i r f o i l s a t Angles o f At tack f rom 0 t o 360 Degrees,"

(Unpublished I n t e r i m Report) WEK-16, W ich i ta S ta te Un ive rs i t y , 1984.

19

APPENOlX AIRFOIL SECTION COORDINATES

The surface contours of the airfoil tested are defined in terms of a station (distance from the leading edge) and an ordinate (distance from the chord line), expressed as a percent of the chord length.

NASA 23024 Airfoil Coordinates

Upper Surface Lower Surface

Station

0 .o

0.277

1.331

3.853

6.601

9.432

15.001

20.253

25.262

30.265

40.256

50.235

60.202

70.162

80.116

90.064

95.036

100.0

Ordinate

0.0

4.017

5.764

8.172

9.844

11.049

12.528

13.237

13.535

13.546

12.928

11.690

10.008

7.988

5.687

3.115

1.724

0.252

Station Ordinate

0.0

2.223

3.669

6.147

8.399

10.577

14.999

19.747

24.738

29.735

39.744

49.766

59.798

69.838

79.884

89.936

94.964

100.0

0.0

-3 303

-4.432

-5.862

-6.860

-7 647

-8.852

-9 703

-10 223

-10.454

-10 278

-9.482

-8.242

-6 664

-4 803

-2.673

-1.504

-0 252

I

NASA 643-621 A i r f o i l Coordinates

Upper Surface Lower Surface

S t a t i o n

-0 085

-0.038

0.083

0.581

1.197

7.045

9.294

15.343

21.432

24.486

30.606

39.798

48.982

58.124

70.224

79.221

88.152

94.076

100.0

Ordinate

0.768

1.223

1.696

2.573

3.298

7.260

8.277

10.401

11.907

12.475

13.276

13.623

12.840

11.296

8.446

5.944

3.353

1.665

0.0

S t a t i o n

-0.085

0 .o 0.459

1.569

3.096

8.455

10.706

13.688

19.616

25.514

31.394

40.202

49.018

60.841

69.776

78.779

87.848

93.924

100.0

Ord inate

0.768

0.0

-0.954

-2.006

-2.851

-4 657

-5.173

-5.741

-6.577

-7.105

-7.364

-7.196

-6.223

-4 268

-2.612

-1.037

0.151

0.502

0.0

21

TABLE 1

T e s t Tip-Speed Reynolds numbers and Tip-SDeed Mach numbers.

4 . 4 0

I C o n f i g u r a t i o n

0.302

NACA 23024 Rotor

NACA 23024 Rotor w i t h 0.30~ A i l e r o n , Gap Open

NACA 23024 Rotor w i t h 0 . 3 0 ~ A i l e r o n , Gap C l o s e d

NACA 643-621 Rotor

Re, Minimum

6 0 . 1 1 x 10

6 0 . 1 1 x 10

0 . 1 1 x lo6

6 0.12 x 10

Maximum

6 0.58 x 10

6 0.37 x 10

6 0.38 x 10

0.56 x l o 6

M -1

Mini mum

0.08

0.10

0.10

0.09

Model

NACA 23024 Rotor

NACA 64 -621

R&or

TABLE 2

performance Canparison

TSR a t cp=o

1 . 5 , 4 . 0 , 8.0

6 . 7

I TSR a t I Maximum

I cp

Maximum cP

5.18 I 0.318

Maximum

0 . 4 3

0.28

0 . 2 8

0 . 4 3

q

( l b / f t2 1

0.0

0 .20

0 -40

0.60

0 -80

1 .00

1 .50

2 .oo 5.00

TABLE 3 Spanwise Flow O b s e r v a t i o n s From T u f t S t u d i e s ( @ 800 RPM).

V

( f t/sec 1

0.0

13.41

18.97

23.23

26.83

29.99

36.74

42.42

67.07

TSR

00

5.20

3.68

3.00

2.60

2.33

1 .90

1.65

1.04

Ret ( m i l l i o n )

0.0839

0.0854

0 -0869

0.0884

0.0899

0.0913

0.0948

0.0981

0.1154

M t

0.0625

0.0637

0.0648

0.0659

0.0670

0.0681

0.0707

0.0732

0 .0867

Spanwise Flow

NACA 23024

none

R o o t t o 0.4-R

R o o t t o 0.5-R

Root t o 0.6-R

R o o t t o 0.6-R

R o o t t o 0.7-R

R o o t t o 0.8-R

R o o t t o 0.8-R

R o o t to 0.9-R

NACA 643-621

none

Root to 0.6-R

Root t o 0.7-R

Root t o 0.9-R

Root t o T i p

23

Reeultant cu

F igu re 1. - Forces on a wind t u r b i n e blade element .

Tlp-rpoed ratio W V W

ANGLE OF ATTACK,

a, (DEG)

I I * I I 0.2 0.4 0.6 0.8 1.0

RADIAL COORDINATE, r / R

F igu re 2. - E f f e c t o f t ip-speed r a t i o on angle of a t t a c k as a f u n c t i o n o f r a d i a l p o s i t i o n along blade.

Vw t

84

\Tunnel ceiling

I- l9 I I I.-

I 4 2

I ' 2 0 D.

I I LStreaml ined strut 1.5 x 3.3 chord

Figure 3. - Hind tunnel t e s t section and instal la t ion o f t es t rotor ( a l l dimensions in inches).

25

.

20.0 c

rAlleron location 5 1 t 3.0 -I I I I I I 1 , I ,

I \ Taper L0.7 thick

(a) Rotor planform (dimensions in inches).

(b) NACA 23024 airfoil. 4

(c) NACA 643-621 airfoil. > rHinge line

I

c- \A Extension plate'

(d) NACA 23024 airfoil with aileron deflected -90' and gap open.

! c

-

F i g u r e 4. - Geometry of test rotors (airfoil coordinates are given in the Appendix).

1 1.00

CT 0.10 -

( a ) Torque coefficient.

0.00 1 1 I I I i

4 . 0 8.0 8.0 10.0 12.0 2.0

"T ' "W

0.48

0. ( 8

0. ir

0. I O

cp O . O @

-0. I 4

-0.24

-0. a4

-0.44

-0. SI

l- I O . o

\ ' 1 4 \ '5 "T ' "W

'8 \ \ ( b ) Power coefficient. ;\

I \ \

1 12.0

Figure 5. - Effect o f TSR on performance o f the NACA 23024 rotor, compared w i t h theory. 27

0

r =

I I I

,

. 'O

';a

0 1 I 1

L

- - - - -

0 0 0

0 - - - - - - - - -

d n V v

w

- - - p - a

- a

E L

0 0 0 m

I 1 1 I 1

O

0 1 I 1 0 a

1 0 w 0

0 0 N 0

0 0 4 0 0 0 N

0 0

0 W

0

0 - 0 Q

0 0 0

0

0

2 0 a, I: c, 0 c, U aJ L

n

L 0 c, 0 L d cu 0 m cu

3 4: z a, r c, cc 0

c 0

U aJ aJ v) n

CT

El cxrcnwwr 0 % -- TCrOllV ( W I W - 1 1 ) 0 16 - - . THKMV ( W I N D - 1 1 ) I 16 - TlQOIlV ( W I N D - 1 1 ) 2 16 --- THEORY ( W I N D - 1 1 ) S 16

2 ' o o 1 1 .50 -

1.00 -

0 . s o - c i e n t .

0 . 0 0 I I 1 1 I 1 i

0.0 2 .0 4 . 0 e. 0 a. 0 IO. 0 1 2 . 0

0.20

0 .10

cp 0 . 0 0

-0. I O ,

- 0 .20

-0. a0

Figure 7. - Effect of TSR on performance of t h e NACA 643-621 r o t o r , compared w i t h theory.

29

0 .

I I 1

0

a w ..

0 0 -

0 I 1

2 .. 0 : 0 0

0 0

0

0 0

0

0 - 0

0 N

0

I

0 0 cu 0

0 a 0 - 0

0 0 .. 0 0

-

I

El'

0

Y

I e >

a 0

0

0 N

E L

0 0 0 d

V - U

1 1 0 0 m - 0 :

N

I 0 0 0 0 0

0

0

.II 0

E L 0 0 0 m n n v

I I I 0 a

0 0

0 0

51 N 0 0 0

0

0

O N

0

0

P

E L 0 0 0 N

a - U

30

i 1.00

( a ) Thrust coefficient.

0.00

CT

o l o 2 . 0 4.0 @. 0 8 . 0 10.0 12.0

v / vw 1

1

0. LO

0.00

. o CP

i -0. 20

(b ) Power coefficient. LII

Q O

- 0 . 8 0

-0 .80

Figure 9. - Performance comparison between the NACA 23024 and NACA 643-621 rotors.

31

)r*cA 28024 KIT00 ,CLEAN )r*cA 84-8-821 ,CLEAN

O . I 0 1

0 . 3 0 <

0.20 -

0. I O -

0 . oe 0 0 ]I;.. 1 . 0

Q Q ' Q

cl Q

J (b) 3000 rpm. "w WS) -0 . I O

o ' s o 1 0.40

0 . 3 0

O . ' O 1

Q

Q

III cl

Q III

Q

Q a 0.00

I I IIII 1 I 1 m

0. 0 1. 0 10.0 11.0 20.0 21.0 80.0

Q Q vw (ws) Q -0 . IO,

-0.20- ( c ) 4000 rpm.

Figure 10. - Power comparison between the NACA 23024 and NACA 643-621 rotors.

1.00 - CT

0.so - (a) Thrust coefficient.

0.00 I 1 I I 1 I 1

0 0 2 .0 4.0 8 . 0 8 . 0 I O . 0 12.0

1

( b ) Power coefficient. A \ \

\, \ \

-0.40

-0. so

Figure 11. - Effect of transition strips on performance of the NACA 23024 rotor at 3000 rpm. 33

T S

I . 0 2 .0 3 . 0 0.00

-0. I O -

ACP 1-Y (ul*lI~ -** ( A V E R ) -0 .20-

(c) Average change in power coefficient.

-0.80 1 +

0. I O O ' I S i 0 . 0 s 1

POWEA

Q

B 0 B

0 A

I -0. IO

-0. I S

+ + (d) Power.

+ +

Figure 11. - Concluded.

1.60

1.00

CT 0. so

f ic ien t .

0.00 I 1 I I 1 1 1

0 0 2.0 4 .0 8 . 0 8 . 0 10.0 12.0

"T "W

. .

( b ) Power coefficient. -0 .40

A -0. so 1

Figure 12. - Effect of transit ion strips on performance of the NACA 643-621 rotor.

35

TS

0 . 0 0

o.oo ~ ;o zio ~

%VT/ vW<7 T m v (wxm-xx)-’

ACP ( A V E R )

- 0.10 (c) Average change in power coefficient.

_ _ I I I I i

4-

0 . 0 s. 0 10.0 IS.0 20.0 25.0 3 0 . 0

1

c1 o TI (CLEAN) Q I TC

A 1 T I + a 16

+ + + + + + +

El B

+

Q

i -0 .05 8 +

-0. IO J (d) Power.

Figure 12. - Concluded.

( a ) A t TSR = a t u f t s a r e chordwise , i n d i c a t i n g no spanwise f low a long the b l a d e s .

( b ) A t TSR = 2.33 t u f t s t u r n r a d i a l l y outward , i n d i c a t i n g spanwise f l o w from hub t o b l a d e t i p s .

F igu re 13. - Typica l flow v i s u a l i z a t i o n results, from tests of the NACA 643-6Zl r o t o r a t 800 rpm (clockwise r o t a t i o n ) .

37

' .so 1 1.00 -

CT

o.so -

=-90.0, OPEN GAP

0 0 _ - - - m I 9 _ _ - - -

@ * - = m - '

( a ) Thrust coefficient.

c] EXPMI- ,CLEAN ,CLEAN - - .

I I I 1

oJo ilo 4.0 8 .0 a. 0 10.0 12.0

CP

'T "W -0. I O

-1.80

I \

i -2 .40

- X ~ O ' ( b ) Power coefficient.

Figure 14. - Effect of TSR on performance of the NACA 23024 rotor with a 30%-chord aileron ful ly deflected and the gap open, compared with theory.

1

0.00 1 I I 1 1 1

2.0 4 .0 e. 0 1.0 10.0 12.0

’T ’W

o ’80 1 0.00

. o

-0.80

CP

i. -2 .40 e Q A Q

- a . 2 0 -I A (b ) Power coefficient.

Figure 15. - Effect o f aileron deflection, gap position, and TSR on performance of the NACA 23024 rotor with a 30lrc-chord aileron.

39

Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

NASA CR-180812 I 4. Title and Subtitle 5. Report Dale

1

Performance and Aerodynamic Braking o f a Hor i zon ta l -Ax i s Wind Turbine from Smal l -scale Wind Tunnel Tests

I J u l y 1987 I

i 6. Performing Organization Code

i I I 1

7. Author(s) 8. Performing Organization Report No. !

I i H.V. Cao and W.H. Wentz, J r .

10. Work Unit No. I I I

9. Performing Organization Name and Address

Wich i ta S ta te U n i v e r s i t y Wich i ta F a l l s , Kansas 67208

I I

11. Contract or Grant No.

NSG-3277 13. Type of Report and Period Covered

2. Sponsoring Agency Name and Address

U. S . Department o f Energy Wind/Ocean Technology D i v i s i o n Washington, D. C . 20545

Cont rac tor Report

DOE/NASA/3277-4 I

5. Supplementary Notes

F i n a l Report. Prepared under Interagency Agreement DE-AI01-76ET20320. P r o j e c t Manager, J.M. Savino, S t ruc tures D iv i s ion , NASA Lewis Research Center, Cleveland, Ohio 44135.

6. Abstract

Wind tunne l t e s t s o f t h r e e 20-inch diameter, zero- tw is t , zero-p i tch wind t u r b i n e r o t o r models have been conducted i n the WSU 7 ' x 10 ' wind tunne l t o determine t h e performance o f such r o t o r s w i t h NACA 23024 and NACA 643-621 a i r f o i l sec t i ons . Aerodynamic 'braking c h a r a c t e r i s t i c s o f a 38 percent span, 30 percent chord, vented a i l e r o n c o n f i g u r a t i o n were measured on the NACA 23024 r o t o r . Surface f l o w pa t te rns were observed using f l uo rescen t m i n i - t u f t s at tached t o t h e s u c t i o n s i d e o f t h e r o t o r blades. Experimental r e s u l t s w i t h and w i t h o u t a i l e r o n s a r e compared t o pre- dictions us ing a i r f o i l sec t i on da ta and a momentum performance code. Resu l ts o f t h e performance s tud ies show t h a t the 643-621 r o t o r produces h ighe r peak power than the 23024 r o t o r f o r a g iven r o t o r speed. A n a l y t i c a l s tud ies , however, i n d i c a t e t h a t the 23024 should produce h igher power. t h a t t he 23024 r o t o r i s much more s e n s i t i v e t o roughness than t h e 643-621 r o t o r . These t rends agree w i t h a n a l y t i c a l p r e d i c t i o n s . Resul ts o f t h e a i l e r o n t e s t s show t h a t t h i s a i l e r o n , when de f lec ted , produces a b rak ing to rque a t a l l t ip-speed r a t i o s . I n free-whee?ing coastdowns t he r o t o r b lade stopped, then r o t a t e d backward a t a t ip-speed r a t l o o f -0.6. Resul ts o f t h e t u f t s tud ies i n d i c a t e t h a t substan- t i a l spanwise f l o w develops as blade s t a l l occurs a t low t ip-speed r a t i o s .

T r a n s i t i o n s t r i p experiments show

7. Key Words (Suggested by Author(s)) 18 Distribution Statement

U n c l a s s i f i e d - u n l i m i t e d Sub jec t Category 44 DOE Category-UC-60

Wind energy; Wind turbine; Aerodynamic performance; Aerodynamic braking; Flow v i sua l i za t i on ; A I leron braking; Wind tunnel t e s t ; Model ro to r t e s t ; Wind tu rb lne model

9 Security Classif (of this report) 20. Security Classif (of this page) 21. No of pages 22. Price'

U n c l a s s i f i e d U n c l a s s i f i e d 40 A0 3