Numerical Study on Aerodynamics of Tandem Wing

International Conference on Science, Technology Engineering and Management

NUMERICAL STUDY ON AERODYNAMICS OF TANDEM WING IN GROUND EFFECT Hari Seshan.B.L1, Aravindraj.E1, Jerin Rakhul.R1, Usha Bharathi.A2 U.G student, Department of Aeronautical Engineering, Jeppiaar Engineering College, Chennai, India 1 Assistant Professor, Department of Aeronautical Engineering, Jeppiaar Engineering College, Chennai, India 2 ABSTRACT: The purpose of this paper is to numerically investigate the aerodynamic characteristics of a tandem wing configuration in ground effect at a Reynolds number 2.87×10 5. The NACA 4415 aerofoil was employed as a section of wings. The simulation of tandem wing in ground effect was performed by Three Dimensional Computational Fluid Dynamic. The analysis of tandem wing has been done for spacing ratio 2.5 i.e. the distance between trailing edge of front wing section and leading edge of rear wing section to the chord length and varying angle of attack 00, 20, 40 in ground effect. The lift coefficient, drag coefficient and, Lift to drag ratio of wing in ground effect is calculated with k-ɛ turbulent model. It is found that the ground effect has strong influence on aerodynamic performance of tandem wing at various angle of attack. The rear wing has low lift coefficient when compared to front wing due to interference effect of wake between two wings. Keywords: Numerical Investigation; Ground effect; Tandem wing; Ange of attack; Lift; Drag. I.INTRODUCTION A wing-in-ground effect can be defined as when an aircraft fly’s close to ground the formation of trailing edge vortex is reduced because the ground partially bocks trailing edge vortex and decrease the amount of downwash generated by wings. This reduction in downwash increases lift of an aircraft and reduces induced drag generated. The German designer Günther W. Jörg developed the Tandem-Airfoil-Flairboat (TAF). Tandem-Airfoil-Flairboat design is built by assembling of two wings with shorter span in tandem configuration. Two wings having same dimensions with small space in between them and doesn’t have horizontal tail. This tandem wing arrangement presents good static stability and controllability in ground effect [1]. Timothy and Yongsheng [2] described that the tandem configuration was tested with four different wing spacing ratios 1.0, 0.5, 0.25 and 0.1 to the chord length. They showed when the spacing ratio is decreased, vortex structures around the rear wing became elongated and spread out due to interactions with the front wing. Total lift of tandem wing was maximum at a wing spacing ratio of 1.0 while thrust was maximum at a spacing ratio of 0.5. Power consumption was minimum at a wing spacing ratio of 0.1. Rafiuddin Ahmed [3] studied experimentally the flow characteristics over a NACA 4415 airfoil at Reynolds number of 2.4×105 by varying the angle of attack from 00 to 100 and ground clearance from five percentage of chord length to eighty percentage of chord length. Separation bubble formed on the lower surface of airfoil for the angle of attack of 00 the laminar separation occurred well ahead of the trailing edge for the angle of attack of 2.50. The flow on the upper surface separated from the wing surface due to adverse pressure gradient for the angle of attack of 100 at small ground clearances and resulting in increased in drag. Pankaj Garg and Neelesh Soni [4] visualized the flow field over NACA 4415 airfoil by varying angle of attack 12 0 to 180 at Reynolds numbers 1×106 and 1.5×106. Coefficient of lift was increased up to 160 at Reynolds number 1.5×106 and after 160 the lift coefficient starts to decrease due to adverse pressure gradient at the trailing edge. Kamma Pradeep [5] described the flow over NACA 4415 airfoil at various Reynolds number. As the Reynolds number increases coefficient of drag also increases and maximum coefficient of lift at Reynolds number 6000. Arthar [6] described pressure distributions on a wing having NACA 4415 airfoi sections with trailing edge flap set at 0 0 and 400. The experimental investigation has been done in the Langley 300-MPN 7- by 10-foot tunnel through different free-stream dynamic pressures and angles of attack to determine the chord wise pressure distributions on NACA 4415 airfoil sections with basic wing and flaps deflected down 40 0 . Saeed-Jame and Adi-Maimun [7] studied the compound wing with one rectangular wing in middle and two taper reverse wings with negative dihedral angle in sides. The negative dihedral angle for taper reverse wing in the sides of compound wing decreases down-wash velocity due to the ground effect this leads to increase in lift coefficient and decrease in drag coefficient of compound wing. The aerodynamic characteristic of tandem wing at high angle of attack depends on position of canard wing because of aerodynamic interference between two wings. The canard in upper position has good coefficient of lift than in middle or lower position [8].The tandem wing is experimentally investigated for close ground proximity. When the tandem wing spacing is low a larger interference effect between two wings and angle of attack 2 0 for both wing lift to drag ratio is maximum[9].

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International Conference on Science, Technology Engineering and Management In current research, a numerical study was carried out to investigate the aerodynamic characteristic of tandem wing in ground effect by fixing front wing angle of attack and varying rear wing angle of attack for spacing ratio 2.5 and ground clearance 0.247. The effect of wake interference between two wings were discussed too.

II.NUMERICAL METHOD Present numerical study was carried out for rectangular wing with tandem configuration having NACA 4415 airfoil as section of wing. The wing specification are shown in Table 1. In this study, the spacing ratio (L/C) is defined as distance between trailing edge of front wing and leading edge of rear wing to the chord length (C), and the ground clearance (G/C) is defined as distance between ground and trailing edge of wing to the chord length C. The rear wing chord (C) was extended to prevent the flow hitting the ground at high angle of attack.

Figure 1. Tandem wing.

Parameter

Units

Front chord (Cf)

0.130 m

Rear chord (C)

0.150 m

Span (b)

0.400 m

Spacing ratio (L/C)

2.5

Ground clearance (G/C)

0.247

Angle of attack (α)

00, 20, 40

Table 1. Wing specification.

The boundary condition at the ground has been set as moving wall with no-slip wall moving at free stream velocity. The upstream boundary condition is velocity inlet and set the velocity as 15 m/s and downstream boundary condition is pressure outlet. The two wings are set to be wall with no-slip boundary condition. The number of nodes for each mesh is about 200000 to 500000 and for refinement the element size over surface of the wing is 4e-03m, the inflation of first layer height 2.4e-03m and maximum layers 3 along the wing surface.

Pressure Outlet

10C

Inlet Velocity V = 15 m/s

10C

20 C

Moving wall V = 15 m/s Figure 2. Sketch of computational domain.

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Figure 3. Meshing of tandem wing

Figure 4. Inflation on wing surface

The numerical simulation are carried out with a FLUENT solver by solving incompressible Navier-Stokes equations with k-ɛ turbulent model at the Reynolds number of 2.87×10 5. The transport equation of k and ɛ are written as, 𝜕(𝜌𝑘) 𝜇𝑡 + 𝑑𝑖𝑣(𝜌𝑘𝑈) = 𝑑𝑖𝑣 [ 𝑔𝑟𝑎𝑑 𝑘] + 2𝜇𝑡 𝑆𝑖𝑗 ∙ 𝑆𝑖𝑗 − 𝜌𝜀 𝜕𝑡 𝜎𝑘 𝜕(𝜌𝜀) 𝜇𝑡 𝜀 𝜀2 + 𝑑𝑖𝑣(𝜌𝜀𝑈) = 𝑑𝑖𝑣 [ 𝑔𝑟𝑎𝑑 𝜀] + 𝐶1𝜀 2𝜇𝑡 𝑆𝑖𝑗 ∙ 𝑆𝑖𝑗 − 𝐶2𝜀 𝜌 𝜕𝑡 𝜎𝜀 𝑘 𝑘 𝜇𝑡 = 𝐶𝜌𝜗𝑙 = 𝜌𝐶𝜇

𝑘2 𝜀

The equations contain five constants 𝐶𝜇 , 𝜎𝑘 , 𝜎𝜀 , 𝐶1𝜀 , 𝐶2𝜀 . The standard k-ɛ model have the following values: 𝐶𝜇 = 0.09, 𝜎𝑘 = 1.00, 𝜎𝜀 = 1.30, 𝐶1𝜀 = 1.44, 𝐶2𝜀 = 1.92

III. RESULT AND DISCUSSION VALIDATION For validation of the data, the pressure coefficient vs position curve is studied. The result obtained from FLUENT for NACA 4415 on front wing section is compared with the experimental data of Carter Laagley [6] for zero angle of attack. In the case of tandem wing in ground effect, the exact experimental data is not available. So the FLUENT data is compared with the coarse mesh to a more refined mesh. The pressure distribution on tandem wing is compared with the coarse mesh to a more refined mesh is shown in Fig. 6. LIFT COEFFICIENT (CL) The lift coefficient has been obtained for different angle of attack by fixing the front wing and adjusting the rear wing angle of attack. Due to interference effect a great reduction in lift coefficient on rear wing when both the wings are fixed at same angle of attack. When the angle of attack is high on the rear wing the interference effect is reduced considerably. The maximum lift coefficient for rear wing obtained when front wing is placed at zero angle and rear wing is at 40 angle. The combined lift coefficient for tandem wing is high when both wings is at 40 angle. The variation of lift coefficient vs angle of attack is shown in Figs. 7 (a), (b), (c). DRAG COEFFICIENT (CD) The drag coefficient has been obtained for different angle of attack by fixing the front wing and adjusting the rear wing angle of attack. For spacing ratio 2.5 when the rear wing angle of attack is smaller than the front wing the drag coefficient is reduced on rear wing, when both wings are fixed at same angle of attack the rear wing drag coefficient is reduced when compared to front wing drag coefficient except for angle of attack 40, where the drag coefficient starts to increase. The variation of drag coefficient vs angle of attack is shown in Fig. 7 (d), (e), (f).

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Figure 5. Data validation for angle of attack 00 of NACA 4415 airfoil.

FLUENT (512971 cells)

FLUENT (888648 cells)

Figure 6. Mesh comparison for pressure distribution over the tandem wing.

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International Conference on Science, Technology Engineering and Management αrear= 00

CL VS AOA front wing"

αrear= 20

CL VS AOA

rear wing"

Front wing

0.6

Rear wing

0.6 0.5

0.4

0.4 CL

CL

0.3

0.2

0.2

0.1 0

0 -1

1

3

5

-1

1

ANGLE OF ATTACK OF FRONT WING (a)

αrear= 40

CL VS AOA Front wing

3

5

ANGLE OF ATTACK OF FRONT WING (b)

CD VS AOA

Front wing

Rear wing

αrear= 00 Rear wing

0.06

0.6 0.05 0.4 CL

CD

0.04

0.2

0.03

0

0.02 -1

1

3

5

-1

ANGLE OF ATTACK OF FRONT WING (c) CD VS AOA

Front wing

Rear wing

1

3

CD VS AOA

αrear= 20

Front wing 0.06

0.05

0.05

CD

0.06

CD

0.04 0.03

5

AOA OF FRONT WING (d)

αrear= 40 Rear wing

0.04 0.03

0.02 -1

1

3

0.02

5

-1

AOA OF FRONT WING (e) Figure 7. Variation of CL, CD of front and rear wing with angle of attack.

1

3

AOA OF FRONT WING (f)

5

L/D VS AOA AOA 0 deg at rear AOA 4deg at rear

AOA 2deg at rear

10 9

L/D

8 7 6 5 4

3 -1

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0

1

2

3

AOA Figure 8. Lift to drag ratio vs angle of attack.

4

5

5

International Conference on Science, Technology Engineering and Management LIFT TO DRAG RATIO (L/D) The lift to drag ratio increases as the angle of attack increased on both wings, for rear wing the lift to drag ratio is reduced when compared to that of front wing due to interference effect between two wigs. The maximum lift to drag ratio is obtained when angle of attack of rear wing is set as 4 0. The variation of lift to drag ratio vs angle of attack is shown in Fig.8. FLOW FIELD ANALYSIS Figs. 9, 10, 11 shows static pressure contours around tandem wing for various angle of attack, it is observed that when the angle of attack increased the static pressure on leading edge and bottom of the wing increases and static pressure on top of the wing decreases. Figs. 12, 13, 14 shows dynamic pressure contours around tandem wing for various angle of attack, it is observed that when the angle of attack increased the dynamic pressure on leading edge and trailing edge of the wing decreases and dynamic pressure on top of the wing increases.

(a)

(a)

(b)

(b)

(c) Figure 9. Static pressure contour on tandem wing 00 AOA at front wing and varying AOA at rear wing.

(c) Figure 10. Static pressure contour on tandem wing 20 AOA at front wing and varying AOA at rear wing.

(a)

(a)

(b)

(b)

(c)

(c)

Figure 11. Static pressure contour on tandem wing 40 AOA at front wing and varying AOA at rear wing.

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Figure 12. Dynamic pressure contour on tandem wing 00 AOA at front wing and varying AOA at rear wing.

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(a)

(a)

(b)

(b)

(c)

(c)

Figure 13. Dynamic pressure contour on tandem wing 20 AOA at front wing and varying AOA at rear wing.

Figure 14. Dynamic pressure contour on tandem wing 40 AOA at front wing and varying AOA at rear wing.

Fig. 15 shows the trailing edge vortices or lift induced vortices on rear wing. These vortices are formed because of finite length of wing. The high pressure region at bottom of the wing interact with low pressure region at top of the wing at wing tip, this interaction create vortices trailing downstream of wing.

Figure 15. Trailing edge vortices.

VI.CONCLUSION In the present work, CFD simulation is carried out to study the flow field and aerodynamic characteristics of tandem wing in ground effect by considering NACA 4415 as section of wings. It is found that the increment of 68.75% of lift coefficient on rear wing when the front wing is fixed at 0 0 angle of attack and rear wing is fixed at 40 angle of attack. The reduction of coefficient of lift is high at rear wing when front wing is fixed at 4 0 angle of attack. The rear wing aerodynamic characteristics is mainly depend on angle of attack at which the front wing is fixed because of interference of wake between two wings. The angle of attack of the rear wing should be higher than angle of attack of front wing to have less interference effect and to achieve maximum coefficient of lift at rear wing when the two wings located in same axis for spacing ratio 2.5. REFERENCES [1] [2] [3] [4] [5]

Rozhdestvensky, K.V., “Wing-in-ground effect vehicles,” Elsevier Journal of aerospace science, Vol. 42, pp. 211-283 (2006). “The Effect of Wing Spacing on Tandem Wing Aerodynamics,” Timothy M Broering and Yongsheng Lian, 28th AIAA Applied Aerodynamics Conference 28 June - 1 July 2010, Chicago, Illinois. “Aerodynamics of a Cambered Airfoil in Ground Effect”, M. Rafiuddin Ahmed, International Journal of Fluid Mechanics Research, Vol. 32, No. 2, 2005. “Aerodynamic Investigation of Flow Field Over NACA 4415 Airfoil,” Pankaj Garg, Neelesh Soni, International Journal of Advanced Research in Scientific, Vol.3, Issue 2, February 2016. “Flow over NACA-4415 aerofoil at Extreme Reynolds number,” Kamma Pradeep, Enugurthi Manasa, Adimulam Neha, International Journal of Advanced Technology in Engineering and Science, Volume No 03, Special Issue No. 01, May 2015.

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International Conference on Science, Technology Engineering and Management [6] [7] [8] [9]

“Pressure distributions on a wing having NACA 4415 airfoil sections with trailing-edge flaps set at 00 and 400 ”, by Arthar W, Carter Laagley Research Center Humpton, Va. 23365, National Aeronautics and Space Administration Washington, D.C. “Aerodynamic characteristics of a compound wing during ground effect” by Saeed-Jame, Adi-Maimun, Agoes-Priyanto, Nor-Azwadi, The International Conference on Marine Technology. “Experimental investigation of the aerodynamic characteristics of tandem‐airfoil based on low Reynolds number”, by ZHANG Guo‐qing & YANG Shu‐xing. “Experimental investigation on the aerodynamic charecteristic of a tandem wing configuration in close ground proximity” by Mohammed Rafiuddin Ahmed and Yasuaki Kohama.

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