Full Thesis.pdf - BUET

Thesis Submitted at the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree. First of all my thanks and gratitude to Allah for the successful completion of this research. Mohammad Ali, Professor and Head, Department of Mechanical Engineering, BUET, Dhaka, for his constant guidance, supervision, inspiration, encouragement and tireless support in this research work and for sharing his in-depth knowledge of experimental research and control flow separation.

It is beyond any doubt that without their help and kind support, it was impossible for me to complete this research work. Finally, I would like to express my sincere thanks to all other teachers and staff of BUET for their cooperation and help in the successful completion of the work.

LIST OF TABLES

NOMENCLATURE

INTRODUCTION

General
Background
Problem Statement
Motivation of the Research Work
Scope and Objectives of the Research
Organisation of the Thesis

For this reason, there is a continuous flow of air around the wing tip from the lower surface of the wing to the upper surface. In aerodynamics, it is suggested that airfoil performance depends on the size/shape of the wing as well as the shape of the wing planes. To determine the aerodynamic characteristics (Pressure Coefficient- Cp, Lift Coefficient-CL, Drag Coefficient-CD and Lift to Drag Ratio-L/D) from static pressure distributions of wing models.

The first chapter covers the background information along with problem statement, scope and objectives of the research. The sixth chapter presents the experimental results and discussion on the important aspects of the results.

Figure 1.1: Typical Drag Breakdown by Components of Transport Aircraft [1]

LITERATURE REVIEW

The aerodynamic coefficients of the wing were calculated from the pressure distribution obtained from the tangential velocities experimentally. The forces were calculated using pressure taps along the centerline of the airfoils. The results show the stall delay of airfoils tested with reduced ground clearance.

Two of the aerofoils tested showed a decrease in CL with decreasing clearance; the third showed an increase. Decreasing headroom was found to reduce the pitch variation of aerofoils with varied angle of attack.

Figure 2.2: Coefficient of Lift and Drag VS AOA and Lift Coefficient/Drag Coefficient VS AOA [28]

AN OVERVIEW OF WING AERODYNAMICS

Wing and Aerofoil
Aerodynamic Characteristics of Wing
General Features of an Aerofoil

Terminologies
NACA Aerofoils

Aerodynamic Forces Developed by Aerofoil
Lift and Drag Coefficient of Airfoil
Aerofoil Data Sources
Co-ordinates of NACA Airfoils

Mean Geometric Chord (C g )
Mean aerodynamic chord (C MAC )
Aspect ratio (AR)
Taper ratio (λ)

Familiarization with Different Wing Planforms

According to Aspect Ratio (AR)
According to Wing Sweep
According to Chord Variation along Span
Variable Planforms
Wing-body Combinations

Selection Criteria to Use NACA 4412

If the wing is sliced with a plane parallel to the x-z plane of the aircraft, the intersection of the wing surfaces with this plane is called an airfoil. Any section of the wing cut by a plane parallel to the xz plane of the aircraft is called an aerofoil. The most forward and rearmost points on the average camber line are the leading edge and trailing edge, respectively.

The last two digits indicate the maximum thickness of the airfoil as a percentage of the chord. This is due to higher airspeed at the upper surface and lower speed at the lower surface of the airfoil as shown in Figure 3.3. The location of this resultant force out of the integration is called the center of pressure.

Lift is always defined as the component of the aerodynamic force perpendicular to the relative wind. Drag is always defined as the component of the aerodynamic force parallel to the relative wind. In addition to lift, a force that directly opposes the wing's motion through the air is always present, which is called the drag force.

The angle between the relative wind and the chord line is the angle of attack of the airfoil. The abscissas, ordinates and slopes of the mean line are indicated as xc, ycand tan respectively. The wing chord can be varied along the span of the wing, for both structural and aerodynamic reasons.

Figure 3.2: Geometric Features of a Typical Aircraft Wing [29]

MATHEMATICAL MODELING

Determination of Pressure Coefficient
Estimation of Aerodynamic Force Coefficients from C P
Design and Construction

Wing Models
Pressure Measuring Device

Experimental Setup .1 Wind Tunnel

Experimental Parameters

Methodology

As shown in Figure 4.2, p acts normal to the surface and τ acts tangential to the surface. The net effect of the p and τ distributions integrated over the entire body surface is the resultant of the aerodynamic force R on the body. In Figure 4.3, U∞ is the relative wind, defined as the speed of the flow far ahead of the body.

The chord c is the linear distance from the leading edge to the trailing edge of the body. The integration of the compressive and shear stress distributions can be done to obtain the aerodynamic forces and moments [29, 38]. In Figure 4.4, the sign convention for θ is positive, measured clockwise from the vertical line toward the direction of p and from the horizontal line toward the direction of τ.

Let us now consider the two-dimensional shape in Figure 4.4 as a cross-section of an infinitely long cylinder of uniform section. As shown in Figure 4.8, both surfaces of the wing section can be divided into small panels corresponding to the total space between each tap location [34]. The aerodynamic characteristics (CL, CD and L/D) can be calculated from the wing's surface pressure distribution as discussed in the previous chapter.

A fixture is fabricated and fixed in the test section of the wind tunnel as shown in Figure 5.4. The experiment is carried out in a 700 mm×700 mm closed circuit wind tunnel, as shown in figure 5.3, available at the turbulence laboratory at the Institute of Mechanical Engineering, BUET. Thus, the 406 mm open flow field created between the outlet channel and the bell mouth inlet becomes the experimental space as shown in Figure 5.4 where the desired velocity is achieved.

Figure 4.1: Pressure Distribution over an Aerofoil’s Surface in terms of C P [29,39]

RESULTS AND DISCUSSIONS

Analysis of Collected Data

Surface Pressure Distributions

Pressure Distributions at - 4˚ AOA
Pressure Distributions at 0˚ AOA
Pressure distribution at 24˚ AOA

The difference between the upper and lower surface pressure of the plan shapes Models 4 and 5 is highest at 20% C. The difference between the pressure on the upper surface and the lower surface of the plan shapes Models 2 and 3 has the highest value from 60% C to 90% C. The difference between the upper and lower surface pressure of the Model 4 and 5 planforms is observed at 20% C.

It is found that the upper surface of the Model-1 planform has a higher suction pressure than the lower surface pressure. The difference between the upper and lower surface pressure of Model-2, 3, 4 and 5 planforms becomes maximum at 40% C. For Model-2 and 3 planforms, the upper surface pressure increases slowly from the leading edge to 60 %.

The difference between the upper and lower surface pressure of Model-2 and 3 planforms becomes maximum at 60% C. For Model-4 and 5 planforms, the upper surface suction pressure is greater than that of the lower surface. The difference between the upper and lower surface pressure of the Model-2 and 3 planforms is observed at a maximum of 20% C.

The difference between the upper and lower surface pressure of Model-2 and 3 planforms becomes maximum at 40% C. The upper surface pressure of Model-2 and 3 planforms is lower than the upper surface pressure of Model-4 planforms and 5. For planform model-1, the bottom surface pressure slowly increases from 20% C to the trailing edge.

The difference between the pressure on the upper surface and the lower surface is maximally observed for the planforms of Model 1. For the planforms of Models 4 and 5, the curves of the upper and lower surface pressure follow the same pattern as those of the planforms of Models 2 and 3 .

Figure 6.1: C p Distribution of Segment-A at α = - 4˚

Lift Characteristics

Drag Characteristics

Lift to Drag Ratio

CONCLUSIONS AND RECOMMENDATIONS

Conclusions

This phenomenon occurred when the tip loss of the swept-edge airfoils (models 2, 3, 4, and 5) decreased due to the reduction in chord length at the tip. From the analysis of the variation of the lift coefficient with the angle of incidence, it is found that the critical angle of incidence for planforms with curved edges (Model-2, 3, 4 and 5) remains around 16˚ than for rectangular (Model-1) ) planforms. The curved trailing edge floorplans (Model-4 and 5) show the best lift characteristics among the five floorplans because they have better lift coefficient, lower drag coefficient and better lift/drag ratio.

It is therefore found that for a given wing area, a wing with a high aspect ratio (Span/Avg Chord) will produce less induced drag than a wing with a low aspect ratio because there is less air turbulence at the tip of ' a longer and thinner wing is . By changing the airfoil section near the wing tips, more lift can be generated closer to the wing root and less towards the wing tip. This allows the curved-edge airfoils to produce more lift due to increased surface area towards the root of the wings.

As a final note, aircraft designers and engineers may consider the curved trailing edge planform model to design a wing model for the purpose of reducing drag for efficient flight.

Recommendations for Future Works

All models must be tested at higher speeds in order to reach the critical Reynolds number. In this research work, the wing concept can be developed to observe the lift coefficient and drag coefficient and compare the results with the aim of developing an efficient wing shape in an aircraft design.

10] Mahmud, M.S., “Performance Analysis of Airfoil with Two-Chamber Surface,” International Journal of Engineering and Technology, Vol. 11] Kandwal, S., and Singh, S., "A Computational Fluid Dynamics Study of Fluid Flow and Aerodynamic Forces on an Airfoil." International Journal of Engineering and Technology, Vol. 12] Robert, M.P., “Variation with Reynolds Number of the Pressure Distribution over an Airfoil Section,” NACA Report no.

14] Wells, A.J., "Experimental Investigation of a Wing with Coflow Jet Flow Control", M Sc Thesis, University of Florida, 2005. M., "Theoretical and Experimental Study of a Forward Swept Wing", Anbar Journal for Engineering Sciences, Vol.3, pp. J., “Interference effect and flow pattern of four biplane configurations using NACA 0024 airfoil”, Proceedings of The International Conference on Mechanical Engineering, Dhaka Bangladesh, 2011.

F., "Experimental Study of Flow Separation Control of an Airfoil by Suction and Injection", Proceedings of the 13th Asian Congress of Fluid Mechanics, Dhaka, Bangladesh, pp. An Experimental Study of the Aerodynamic Characteristics of NACA 4412 Aerofoil with Curved Edge Planform ”, M.Sc. 33] Ramesh, P., "Numerical and Experimental Investigation of the Effect of Geometry Modification on the Aerodynamic Characteristics of a NACA Wing", M.Sc.

39] Mainuddin, M., and Ali, M.A.T., “Experimental Investigation of Lift to Drag Ratio between Volume Equivalent Airframes”, Proceedings of the 4th International BSME-ASME Conference on Thermal Engineering, Dhaka, Bangladesh, p. 44] Kandwal S, ., and Singh, S., "Computational fluid dynamics study of fluid flow and aerodynamic forces in an airfoil", Int. T., "Computational Fluid Dynamics Analysis of Wind Turbine Blade at Different Angles of Attack and Different Reynolds Numbers," Procedia Engineering, vol.

UNCERTAINTY ANALYSIS

APPENDIX-II