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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.svg8/7/2019 Aero Dyan Mics
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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