Aerodynamics of Road Vehicle.pdf
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Transcript of Aerodynamics of Road Vehicle.pdf
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Aerodynamics of Road Vehicle
Prof. R. Krishna Kumar
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Aerodynamics
Aerodynamic Resistance
Air flow over the exterior of the body ~ 90 % loss
Air flow through the radiator system and the interior for cooling and heating ~10%
External Airflow
Normal Pressure called pressure drag ~ 90 % external Resistance
Shear stress resulting in skin drag significant for large vehcile
In practice the aerodynamic resistance is expressed as 2a 2R rfD VAC
=
Af : Characteristic area of the vehicle 79 to 84 % projected area ; Vr : Speed; Horse Power increases as V3
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Why does one study Aerodynamics
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Nomenclature of the body of a car
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Airplane and Vehicle Aerodynamics Combination shape of Jaray
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Drag Coefficients of the mid 90s car
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Drag Coefficient with Time
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Cars of the 70s. Note the similarities
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Types of Cars
Squareback
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The vortex behind the car
quasi 2D flow separation
3D vortex rich in energy
Dead Water
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Flow Seperation
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Pressure Coeff. Of a bluff body
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)2/()(
2
=VppCp
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- laminar separation
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Pressure Distribution
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The vortex behind the car
quasi 2D flow separation
3D vortex rich in energy
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A pillar vortex
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Force on the side glass
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Flow Field around a car
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The Rear Wake
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Optimization of Front End Design Volkswagen Golf I
Lower Stagnation point gives better drag
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Reduction of Drag by rounding or Chamfering the front end edge
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Drag Reduction by Fine tuning the hood radius and grille design
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Important Angles in the front
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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The Effect of Roof
There is no flow towards the side of the roof
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The hair raising problem
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Less than 30 deg At 30 deg.
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Notchback
Does the flow reattach in the trunk ?
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Fastback and Hatchback Volkswagen Golf I
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Fastback and Hatchback Polo I
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Effect of Rear Length
The effects are to be seen in conjunction with side edges of the slant are well rounded
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Rear Height and Drag Coefficient
For a rounded contour the height is the most important
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Interference Effect
1. =25; = 0 2. =25; = 10 3. =25; = 10; = 10 4. 3+chamfered top
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Roof and Side Part
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Rear Spoiler
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Rear Spoiler profile
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Is optimization of the geometry in a notchback a simple affair?
The flow is affected by: 1.The radius of the roof and the rear window 2.Geometry of the end of the trunk lid 3.Design of the C pillar, their taper, radius and trailing edge
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Reduction of Drag thru the rear diffuser
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Plan view camber and drag
Notchback Fastback
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Flow under the body
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Front Spoiler optimization
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Front Spolier Velocity distribution underneath a car
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Front Spoiler and pressure distribution
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Drag reduction by smoothing the underbody
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Opel Calibra
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Wheel Arch effect
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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Rounding of A pillar and C pillar
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Windshield and hood
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Profiles to note The concept of parametric Design
CD of thin line 0.43; Bold line 0.3
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The Rear End Geometry
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The window effect
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EPA test cycle
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Drag and weight effect
Compact car
Full size car
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European Driving Cycle
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Fuel consumption
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Fuel Consumption of a 40 Ton Tractor- Trailer
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Fuel Consumption of a 40 Ton Tractor- Trailer and Cd
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Fuel Consumption of inter-city bus
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Fuel Consumption of inter-city bus and Cd
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Flow around the box
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Flow over and around the truck
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Gap width and Cd
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Cd reduction
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Aerodynamic Design