aero dyan mics

8/7/2019 Aero Dyan Mics

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Presented By:Eugene Tan

AERODYANMICS


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Shell/Aerofoil Design1. FundamentalsObjectives of the designAerofoil design limitations

Four forcesAerofoil design2. Aerodynamic drag

Skin friction drag, Pressure drag, Induced dragParasite drag, Form drag

3. Aerodynamic of side profile4. Significance of Aerodynamic drag5. Summary: Drag reduction6. Examples of Body Shape

NVT (2011)


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Objectives of the designKey ObjectiveReduce running resistance acting on the entire body of the carTwo main factors of running resistance

Rolling resistanceAerodynamic drag

Light in weight & have minimal surface areas (such asfrontal area and side profile)Streamlined bodies to prevent flow separation as itcauses high drag force


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Aerofoil Design LimitationsDesign of the Solar car is limited by:1. Race regulations

2. Aerodynamic needs3. Restrictions on solar power/area


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Four Forces

In unaccelerated level flight, Lift is equal and opposite toWeight , and the Thrust is equal and opposite to Drag

Imbalance of the forces will cause a change in speed or

altitude of the airplane. Lift produced by an airfoil is thenet force developed perpendicular to the relative wind


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Aerofoil Design
http://en.wikipedia.org/wiki/File:Airfoil.svg


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Aerodynamic DragAerodynamic drag consists of four components:

1. Skin Friction drag

2. Pressure drag3. Induced drag4. Parasite drag


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Skin Friction DragSkin friction drag depends on:

1. Type of flow over the body Laminar flow has lower surface drag compared to turbulent

2. Roughness of the surfaceRougher surface, more skin friction

3. Amount of area

More surface area, more drag


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Pressure DragPressure drag results due to the pressure differencebetween the forward facing surface and the rear facingsurface

Front has higher pressure compared to rearPressure difference causes a net rearward drag forceReduced by having smooth surfaces and avoiding sharpcornersCorners and bends should be tapered gradually Also known as boundary layer pressure loss

Boundary layer gets thicker from front to rear,less pressure at rear

Front

Rear


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Induced DragInduced drag , also called trailing vortex drag which isdue to the pressure difference between the top andbottom surface of the car

Pressure difference causes air to flow up the sides from thehigher pressure bottom, resulting in vortices in the wakebehind the carShould maintain same pressure is design for both the topand the bottomHowever, it depends


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Parasite DragParasite drag is due to imperfection of the surface,seams and any additional add-ons on the surface of thecar that is protruding out from the body

Present in expose wheelsDoes not always cause drag might result in lift


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Form DragForm drag is a resistance to the smooth f low of air.The shape of something may create low-pressure areas

and turbulence which retard the forward movement of the aircraft (see figure 4-9).Streamlining eliminate form drag


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Aerodynamic of Side ProfileIncrease area of side profile, represent higher loss of energy When beta increases, value of drag coefficients increasesThe coefficients can be reduce by reducing the effectivecross sectional areaIf poorly design, the car would not be able to reach highspeed as it will become very difficult to control as speedincreases or experiencing high crosswinds


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Significance of Aerodynamic DragAccording to the graph shown, the ratio of theaerodynamic drag to the total running resistance,

is 4:1 at 100km/hr10% reduction in aerodynamic drag2.5km/hr increase in average speed20km increase in distance


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Summary: Drag Reduction1. Driving force required to cruise is a function of

aerodynamic drag

2. Aerodynamic drag increases proportionately tothe square of speed3. Drag reduction is achieved by reducing drag

coefficient of the shell/airfoil

4. Achieved by designing an aerodynamic shell,reducing frontal area and minimizing the liftproduced


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Body Shape

Manta-Type (MIT) Thicker body with a sloped front Prevents flow separation

Bubble Canopy (Nuna 5) Thin body & bubble canopy Minimal side profile & frontal area Canopy created significant lift

Prefered! Simpler array construction and layout

Uniform exposure of solar cells to sunlight

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