Aerodynamics of Road Vehicle

Prof. R. Krishna Kumar

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

Why does one study Aerodynamics

Nomenclature of the body of a car

Airplane and Vehicle Aerodynamics Combination shape of Jaray

Drag Coefficients of the mid 90s car

Drag Coefficient with Time

Cars of the 70s. Note the similarities

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Types of Cars

Squareback

The vortex behind the car

quasi 2D flow separation

3D vortex rich in energy

Dead Water

Flow Seperation

Pressure Coeff. Of a bluff body

)2/()(

2

=VppCp

- laminar separation

Pressure Distribution

The vortex behind the car

quasi 2D flow separation

3D vortex rich in energy

A pillar vortex

Force on the side glass

Flow Field around a car

The Rear Wake

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Optimization of Front End Design Volkswagen Golf I

Lower Stagnation point gives better drag

Reduction of Drag by rounding or Chamfering the front end edge

Drag Reduction by Fine tuning the hood radius and grille design

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Important Angles in the front

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

The Effect of Roof

There is no flow towards the side of the roof

The hair raising problem

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Less than 30 deg At 30 deg.

Notchback

Does the flow reattach in the trunk ?

Fastback and Hatchback Volkswagen Golf I

Fastback and Hatchback Polo I

Effect of Rear Length

The effects are to be seen in conjunction with side edges of the slant are well rounded

Rear Height and Drag Coefficient

For a rounded contour the height is the most important

Interference Effect

1. =25; = 0 2. =25; = 10 3. =25; = 10; = 10 4. 3+chamfered top

Roof and Side Part

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Rear Spoiler

Rear Spoiler profile

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

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Reduction of Drag thru the rear diffuser

Plan view camber and drag

Notchback Fastback

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Flow under the body

Front Spoiler optimization

Front Spolier Velocity distribution underneath a car

Front Spoiler and pressure distribution

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Drag reduction by smoothing the underbody

Opel Calibra

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Wheel Arch effect

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

Rounding of A pillar and C pillar

Windshield and hood

Profiles to note The concept of parametric Design

CD of thin line 0.43; Bold line 0.3

The Rear End Geometry

The window effect

EPA test cycle

Drag and weight effect

Compact car

Full size car

European Driving Cycle

Fuel consumption

Fuel Consumption of a 40 Ton Tractor- Trailer

Fuel Consumption of a 40 Ton Tractor- Trailer and Cd

Fuel Consumption of inter-city bus

Fuel Consumption of inter-city bus and Cd

Flow around the box

Flow over and around the truck

Gap width and Cd

Cd reduction

Aerodynamic Design