aerodynamic study of slot effect on clarky-14 in low speed

International Journal of Art & Humanity Science (IJAHS)

www.ijahs.com Volume 3 Issue 5, (Sept-Oct 2016), PP.21-29

Page | 21

Aerodynamic study of Slot Effect on

ClarkY-14 in Low Speed Wind Tunnel Asst. Prof. Dr. Eng. Mohammed Kheiraldeen Abbas

Mechanical Engineering Department, Al Nahrain University, Baghdad/Iraq

[email protected] ,009647700423491

Eng. Hasan Khudhur Abbas

Mechanical Engineering Department, Al Nahrain University, Baghdad/Iraq

[email protected], 009647804041433

Abstract: Slotted airfoil affects the lift coefficient CL and stalling angle when deployed. The shape and gap between

auxiliary airfoil and the main wing make huge impact on lift and stalling angle. In this study, a slotted Clark Y-

14 airfoil is made according to the results of numerical analysis using Javafoil. Multiple configurations have

been tested, and the best ones are used to generate the final configuration. An actual model based on the final

configuration has been made. It is tested using the educational wind tunnel (EWT). The chord of slotted airfoil

is 90mm when closed and have span of 250mm. The slotted airfoil is tested at a velocity of 35 m/sec at an angle

ranging from -5° to +25°. The airfoil has been tested when the slot is open, and closed. Later this configuration

is modified by adding a slat over leading edge with chord of 25.2mm and span of 250mm.

KEYWORDS: Clark Y-14, lift, wind tunnel tests, high lift devices, slot, airfoil.

1. INTRODUCTION

There are many types of high lift devices. These include- but are not limited to- spoilers [1] which have the

job of reducing lift, flaps [2] which are attached to the end of wings, slats which could exist in front of or above

the airfoil, and slots. This study focuses on using a slotted Clark Y-14 airfoil with a slat above its leading edge.

2. LITERATURE REVIEW

Carl and Shortal [3] used a vertical wind tunnel with a diameter of 5 feet (1.524 meters). A slotted Clark

Y-14 wing had been tested. The cord of the wing was 25 cm. Wind speed was 35 meters/sec. The wing was

made from laminated mahogany, while the slat was made from aluminum alloy because the slat was small in

size. The experiment took into consideration 100 positions where the slot gap, slot width, and slot depth had

been changed. The range of slot gap started from 1.5 to 3.5% of the chord, 3.35 to 15% of the chord for slot

width, and finally the slot depth was tested from 3.5 above to 4% chord below the main wing. The angle of

attack had been changed from -6 to 46 with a Reynolds number of 609000. It was found that the best slot width

was 14.7% of the chord, and slot depth of 4% of the chord. Carl found that the lift has been increased by 41.5%,

with an angle of attack increase of 13 degrees. The critical angle of attack was found to be 30 degrees. Carl

concluded that the shape and size of slat was not as important as the distance and the angle of the slat from the

main wing.

mailto:[email protected]

mailto:[email protected]



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Fred and Carl [4] tested the characteristics of Clark Y-14 with low drag fixed slots. A number of tests

were being conducted first to find the best probable slot arrangement. Next, the best possible auxiliary airfoil

shape and position were determined. Then, the effect of rounding the nose of main wing was evaluated, and

finally the effect of moving the slot further back form leading edge was checked. The experiment had been

conducted using a vertical wind tunnel with a 5 feet diameter (1.524 meters) with a Clark Y-14 wing having a

chord of 25.4 cm. The angle of attack had been changed from -6 to 40 degrees. Air flow was 35 m/sec. Fred

figured out the best position for slot from his previous study [3]. Next, Fred found that the drag was less when

the nose of the auxiliary airfoil is rounded. It was also found that the change of the nose of the main wing to be

rounded gave best results when the radius of rounding was 2% of the chord. Finally moving the slot back from

the leading edge gave a slight increase in lift. The best lift coefficient was 1.751 which indicated that an

improvement of 34.6% has been achieved. The angle of attack increased from 15 to 24 – which is 9 degrees

improvement – using a slotted wing. The least drag for the wing with fixed slot improved by 52.6%.

Fred and Joseph [5] studied the effect of multiple fixed slots for Clark Y-14 wing with a trialing edge

flap on lift and drag. In this study, the wing had four fixed slots. Tests were done in a vertical wind tunnel with

5 feet in diameter (1.524 meters). The chord of the wing was 25.4 cm, and the angle of attack was ranging from

-6 to 40 degrees, while the airspeed was 35 m/sec. Results from this study showed that lift has been improved

by 37%. Fred found that increasing the number of slots beyond one does not improved lift coefficient, for this

reason Fred concluded that only one slot is enough to improve the lift from 1.291 to 1.772, and improve the

angle of attack from 15 to 24.

Makawana el al [6] studied a fixed slot on NACA 0012 wing. The chord of the wing was 1 meter.

Airspeed was 5 m/sec. The angle of attack had been changed until the critical angle of attack was reached. After

that a slot that was 15% of the chord had been tested with different angles. Two turbulence models had been

studied.

3. Configuration of Slotted Clark Y-14

Since slots and slats improve lift, it is suggested in this work to use a slat with a slot. A slot could be

opened or closed, while a slat could be placed in front of the leading edge, or above it. In order to find the best

configuration for using a slot with a slat, the state of slot is tested independently, meaning that an open and a

closed slot are being tested, and the result of lift coefficient is being checked. This is shown in Fig. 1:

Closed Slot Open Slot

Fig. 1. An open and closed slot configuration



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The same procedure is performed on the slat. The slat is placed at different heights above the leading edge, and

the height resulting in best lift is selected (see Fig. 2).

4mm 6mm

8mm 10mm

12mm Fig. 2: Slat above leading edge

Next, the slat is tested by rotating it at different angles. The angle with the highest lift is selected (see Fig. 3).

Rotation by 0 Degrees Rotation by -5 Degrees Roation by -10 Degrees

Fig. 3: Rotated slat above leading edge

Finally, the slat height and rotation that result in best lift, and the best slot configuration are chosen as shown

in Fig. 4.



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Fig. 4: Open slot with slat above leading edge configuration

4. Experimental Results

The experiments used Reynolds number of 2.1x105, and wind speed is assumed to be 35 m/sec. The

airfoil chord is 90mm, and span is 250mm. The slot chord is 14.7% from main chord (which is about 13.23mm)

with a span of 250mm.

For the first configuration, where a slot is being open and closed, the lift coefficients are shown in Fig.

5. The figure shows that an open slot gives better lift performance than a closed one.

Fig. 5. Effect of open and closed slot on lift coefficient.

Next, the second configuration is used where the slat is placed above the leading edge. The slat is placed

at 4mm, 6mm, 8mm, 10mm, and 12mm. Fig. 6. shows that a slat placed at a height of 12mm results in better

lift performance than other heights.

-0.5

0

0.5

1

1.5

2

2.5

-5 0 5 10 15 20 25 30

Lift

Co

effi

cen

t (C

L)

Angle of Attack (AOA)

CLOSE SLOT OPEN SLOT



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Fig. 6: Effect of moving slat above leading edge at different heights using JavaFoil.

The next experiment rotates the slat at height 12mm, by 0°, -5°, and -10°. Results of such rotation are

shown in fig. 7.

Fig. 7. Effect of Rotating Slat with Height of 12mm with Clark Y-14 on Lift using JavaFoil.

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

-5 0 5 10 15 20 25 30

Lift

Co

effi

cie

nt

(CL)


4mm 6mm 8mm 10mm 12mm

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

-5 0 5 10 15 20 25 30

Lift

Co

effi

cie

nt

(CL)


12mm WITH 0 DEGREE 12mm WITH -5 DEGREEE 12mm WITH -10 DEGREE



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Results show that a rotation angle of -10⁰ gives best lift. So, the location and angle for the slat is (12mm

above leading edge, with -10⁰ rotation). The last experiment uses an open slot and a slat such that the slat is

placed above leading edge at 12mm rotated by -10⁰. Results are shown in Table 1, and Fig. 8.

Fig. 8. Performance of Different Clark Y-14 Configuration in JavaFoil.

Table 1. JavaFoil, Optimum Position for Different Configurations.

Open Slot Aux at 12mm Aux at 12mm

rotate -10

Open Slot + Aux at

12mm rotate -10

ANGLE CL CL CL CL

α ⁰ [-] [-] [-] [-]

-3.5 -0.086 0.066 -0.066 -0.082

-2.5 -0.01 0.183 0.097 -0.044

-1.5 0.046 0.3 0.21 0.026

-0.5 0.113 0.417 0.317 0.097

0.5 0.183 0.532 0.43 0.171

1.5 0.257 0.646 0.545 0.249

2.5 0.407 0.758 0.659 0.417

3.5 0.503 0.866 0.772 0.411

4.5 0.605 0.968 0.884 0.504

5.5 0.603 1.065 0.996 0.604

6.5 0.705 1.154 1.105 0.709

7.5 0.812 1.234 1.208 0.819

8.5 0.922 1.307 1.306 0.931

9.5 1.034 1.368 1.4 1.045

10.5 1.145 1.424 1.485 1.158

11.5 1.255 1.472 1.56 1.269

12.5 1.355 1.51 1.627 1.371

13.5 1.453 1.373 1.682 1.469

14.5 1.548 1.382 1.724 1.565

15.5 1.638 1.387 1.748 1.656

-0.5

0

0.5

1

1.5

2

2.5

-5 0 5 10 15 20 25 30

Lift

Co

effi

cie

nt

(CL)


AUX AT 12mm AUXT AT 12m + Rotate -10

OPEN SLOT OPEN SLOT + AUX 12mm Rotate -10



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16.5 1.725 1.387 1.751 1.744

17.5 1.807 1.38 1.714 1.826

18.5 1.882 1.367 1.693 1.902

19.5 1.946 1.349 1.694 1.967

20.5 2.002 1.325 1.688 2.022

21.5 2.044 1.297 1.67 2.068

22.5 2.078 1.265 1.645 2.108

23.5 2.112 1.23 1.612 2.144

24.5 2.12 1.192 1.573 2.163

Results show that using a slat with open slot gives the best lift compared to other configurations. To

check the accuracy of these results, a series of tests using the real models are performed. Results of these tests

are shown in Table 2, and Fig. 9. It can be seen that actual experiments result in similar behavior to that of

JavaFoil, where an open slot with slat above leading edge result in better performance than other configurations.

Fig. 9. Performance of Different Clark Y-14 Configuration in EWT.

Table 2. EWT, Optimum Position for Different Configurations.

Open Slot Aux at 12mm Aux at 12mm +

Rotate by -10

Open Slot + Aux at

12mm Rotate -10

ANGLE CL ANGLE CL ANGLE CL ANGLE CL

α [-] α [-] α [-] α [-]

[°] [-] [°] [-] [°] [-] [°] [-]

-4.9 -0.0970 -5.1 0.0951 -5.1 0.0521 -4.9 -0.231

0 0.2030 0 0.58756 0 0.5 0 0.018

5 0.4709 5 1.13481 5 1.034 5 0.399

9.9 0.805 11 1.474 11 1.5 10 0.850

15 1.071 12 1.358 12 1.4 15 1.229

17.2 1.268 15 1.277 15 1.364 17.2 1.432

18 1.314 20 1.187 20 1.232 19.9 1.595

20 1.402 ---- ------ ------ ----- 22.1 1.690

22.1 1.408 ----- ------ -------- ----- 25 1.65

-0.5

0

0.5

1

1.5

2

-10 -5 0 5 10 15 20 25 30

Lift

Co

effi

cie

nt

(CL)


AUX AT 12mm AUXT AT 12m + Rotate -10

OPEN SLOT OPEN SLOT + AUX 12mm Rotate -10



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23.7 1.416 ------ ------ ------ ------ 25.1 1.64

24.9 1.415 ------ ----- ------ ----- 25.4

1.64

Fig. 10.Clark Y-14 as Sketched and manufactured

3 4

2 1



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Fig. 11. Educational wind tunnel (EWT) and Clark Y-14 with slats in test section

5. Conclusion

In this study, different airfoil configurations have been used to figure out the best parameters for using

a slot with a slat. It is found that an open slot performs better than a closed one. As for slats, the higher the

location of the slat above leading edge, the better, so 12mm is the best location for a slat. Also, rotating the slat

by -10 degrees results in ever better results. By combining the parameters resulting in best performance for

these configuration, an open slot with a slat above leading edge, rotated by -10 degrees gives the best possible

lift compared to other techniques.

References

[1] Mohammed Kheiraldeen Abbas; AMER QADER HAMEED (2015): AERODYNAMIC STUDY OF A NEW CONFIGURATION OF

SPOILER ON A MODEL WING IN LOW SUBSONIC WIND TUNNEL, International Journal of Art & Humanity Science (IJAHS) e-

ISSN: 2349-5235, www.ijahs.com , Volume 2 Issue 5, PP. 26-35.

[2] Mohammed Kheiraldeen; Ahmed Hamid (2014): EXPERIMENTAL STUDY TO THE EFFECT OF GURNEY FLAP ON THE

CLARK Y-14 AIRFOIL WING MODEL, International Journal of Innovation and Scientific Research, ISSN 2351-8014 Vol. 9 No. pp.

120-132.

[3] W., Carl J; A. Shortal, J. “The Aerodynamic Characteristics of a Slotted Clark Y Wing as Affected by the Auxiliary Airfoil Position”,

NACA-TR-400, Date Acquired: Sep 01, 1996, 1932.

[4] W., Fred E; W., Carl J, “The characteristics of a Clark y wing model equipped with several forms of low-drag fixed slots,” NACA-

TR-407, Date Acquired: Sep 01, 1996, 1933.

[5] W., Fred E; S., Joseph A, “The effect of multiple fixed slots and a trailing-edge flap on the lift and drag of a Clark Y airfoil,” NACA-

TR-427, Date Acquired: Sep 01, 1996.

[6] P. Makwana B. and J. makadiya J., “Numerical Simulation of Laminar Flow over Slotted Airfoil,” IOSR Journal of Mechanical and

Civil Engineering (IOSR-JMCE), e-ISSN: 2278-1684,p-ISSN: 2320-334X, Volume 11, Issue 4 Ver. II, PP 64-71, Jul- Aug. 2014.

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aerodynamic study of slot effect on clarky-14 in low speed

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