reduction of skin friction drag in aircraft wings(NACA 0012 airfoil) by employing surface roughness Prepared By S.S.Pon Sudhir Sajan AP/ Aeronautical Engineering/NIU For Research Colloquim

In this research a methodology to reduce the drag by creating roughness over wing surface has been adopted. Since the flow transition is from laminar to turbulent around the half chord, the turbulent region will produce less drag when the surface is rough. By this concept this research is being carried out. The effects of roughness on the wake characteristics of a wing can delay the flow separation, operating in a compressible, high-speed environment. NACA 0012 airfoil was selected for this study. Computational Fluid dynamic analysis has been done by creating the models and mesh for wing with and without surface roughness. Similarly Aluminum wing models are fabricated with and without surface roughness and same has been tested in Wind Tunnel. The results are discussed in terms of Lift and Drag. ABSTRACT

Literature review Kousik Kumaar et al., [1] In this research a methodology to reduce the drag using the riblets over wing surface has been adopted. R.Jones and D.H.Williams [2] in 1936 investigated the effect of surface roughness on characteristics of airfoil NACA 0012 and RAF 34. John A. Zalovcik et al., [3] studied the effect of roughness on wing profile drag with transition fixed far forward.

PROBLEM IDENTIFICTION The effect of roughness changes the aerodynamic characteristics of the wing. Creating roughness will reduce the coefficient of skin friction drag or viscous drag and increase the coefficient of lift. Although much data are already available on the wakes produced by smooth bodies but no experiments has been done to study the influences of body roughness on wake flow characteristics. To remedy this deficiency, the present study considers the effects of surface roughness on the wake characteristics of a wing operating in a compressible, high-speed environment.

METHODOLOGY The formation of wake over the wing due to boundary layer separation causes a dramatic increase in drag which leads to increased fuel consumption and results as a lag in effectiveness of the wing. The idea to reduce drag by means of implementing roughness over the upper surface eliminates the wake formation. Wake formation is delayed or nullified by altering the flow separation, thus increasing the L/D ratio. The effect of roughness changes the aerodynamic characteristics of the wing by reducing skin friction drag or viscous drag.

NACA 0012 aerofoil is selected for this study. Computational Fluid dynamic analysis has been done by creating the models and mesh for wing with and without surface roughness. Aluminum wing models are fabricated with and without surface roughness and same has been tested in Wind Tunnel. The results are discussed in terms of Lift and Drag. The wing made with surface roughness experience an increase in aerodynamic efficiency

MODELLING With the coordinates of NACA0012 aerofoil, wing model has been designed using CATIA.

Design of wing Without Roughness

Design of wing With Roughness

Meshing

Coefficient of Lift and Drag for wing without surface roughness 2 degree angle of attack

4o angle of attack

6 degree angle of attack

8 degree angle of attack

Coefficient of Lift and Drag for wing without surface roughness 2o angle of attack

4o angle of attack

6o angle of attack

8o angle of attack

Results for wing without roughness Angle of attack α Lift L Drag D Coefficient of Lift CL Coefficient of Drag CD CL/CD 2 7.37 2.85 0.0024 0.0012 4 14.37 3.06 0.0047 0.0013 3.615 3 21.40 3.78 0.0071 0.0015 4.73 8 28.711 4.93 0.0095 0.0019 5

Results for wing with roughness Angle of attack α Lift L Drag D Coefficient of Lift CL Coefficient of Drag CD CL/CD 2 7.13 2.013 0.0023 0.00067 3.43 4 14.14 2.232 0.0047 0.00074 6.35 6 20.985 2.805 0.0069 0.00093 7.41 8 27.972 3.845 0.0093 0.0012 7.75

Comparison of CL/CD Angle of attack α CL/CD Without roughness With roughness 2 3.43 4 3.615 6.35 6 4.73 7.41 8 5 7.75

By comparing the above two graphs it is found that the wing with surface roughness has more L/D ratio than that without roughness. Therefore the wing with surface roughness has more aerodynamic efficiency.

EXPERIMENT Fabrication 6061-T6 Aluminum Sheet / Plate are frequently found in aircraft construction. Mechanical properties of 6061-T6 Aluminum Sheet Modulus of Elasticity 68.9 GPa Ultimate Bearing Strength 607 MPa Poisson's Ratio 0.33 Fatigue Strength 6.5 MPa Shear Strength 207 MPa Density 2.7 g/cc

Fabricated wing model without roughness

Fabricated wing model with roughness

Aspect Ratio In aeronautics, the aspect ratio of a wing is the ratio of its span to its aerodynamic breadth or chord. AR = 𝑏 2 𝑆 b = 19.7 cm S = 19.7 X 14.5 = 285.65 cm2 AR = 19.7 2 285.65 = 1.35

Wind Tunnel Specification of Wind Tunnel used Test Section : 0.3 X 0.3 m Air speed : maximum of 70 m/s Overall size : 6m Power required : 7.5 HP motor with 900 rpm

Lift equation is 𝐿= 1 2 ρ v2 S CL CL= 2𝐿 ρ 𝑉 2 S 𝐶 𝐿 Drag equation is 𝐷= 1 2 ρ v2 S CD CD= 2𝐷 ρ 𝑉 2 S 𝐶 𝐷 V = 70 m/s S = 2.86m2

Testing of wing without surface roughness

Experiment result for wing without surface roughness Angle of attack α Lift L   Drag D Coefficient of Lift CL Coefficient of Drag CD CL/CD 2 23.94 10.26 0.0028 0.0012 2.3 4 36.78 13.68 0.0043 0.0016 2.69 6 55.59 14.5 0.0065 0.0017 3.82 8 76.12 16.25 0.0089 0.0019 4.7

Experiment for wing without surface roughness

Experiment result for wing with surface roughness Angle of attack α Lift L Drag D Coefficient of Lift CL Coefficient of Drag CD CL/CD 2 22.2 5.90 0.0026 0.00069 3.76 4 35.06 5.98 0.0041 0.00070 5.86 6 52.17 7.61 0.0061 0.00089 6.85 8 83.82 11.11 0.0098 0.0013 7.5

The above result shows that, as the angle of attack increases the value of CL/CD also increases for the wing with surface roughness also.

When we compare the CL/CD values of wings with and without roughness, the skin friction drag for wing with surface roughness falls and because of this we get a high increased value of CL/CD. Therefore from the above Computational Fluid dynamic analysis and wind tunnel experiment it is proved that, by adding surface roughness over the wing surface can reduce the skin friction drag. Thus the aerodynamic performance can be improved by adding surface roughness over the wing.

Reference 1. Kousik Kumaar et al., July-2015. ‘’Reduction of Skin Friction Drag in Wings by Employing Riblets’’ 2. Jones.R et al., (1936), “Effect of surface roughness on characteristics of airfoil NACA and RAF 34” 3. John A. Zalovcik et al., [3] A flight investigation of the effect of surface roughness on wing profile drag with transition fixed.

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