Explain the aerodynamic forces and moments acting on vehicle in dynamic condition
Answers
(1) Aerodynamic drag:.
Aerodynamic means the behavior of the air motion relative to the car body. Aerodynamic drag is also called as air resistance.
Air drag force acts in the direction of vehicle motion.
The total aerodynamic drag of a vehicle include many factors such as profile drag (57%), induced drag (8%), skin friction (10%), interference drag (15%) and cooling and ventilation drag (10%).
Stream line of air flow around the vehicle should be continuous and separation of the boundary layer with its attendant vertices should be avoided. Skin drag coefficient should be decrease by smooth and well-polished of body surface.
The accessories such as mirror, door handle aerials and badges which project outward from normal surface of body produce interference drag and projection below the vehicle such as axle, propeller shaft, tow bar also contribute interference drag hence such projection should be avoided.
(2) Aerodynamic lift:
It is the vertical component of the resultant force caused by the pressure distribution on the vehicle body.
The aerodynamic lift and pitching moment are undesirable effects. The aerodynamic lift tends to reduce the pressure between the tyre and the ground. This causes the loss of steering on the front axle and loss of traction on the rear axle.
Pitching causes rear wheel lift off the ground and reduces available traction. It is the rocking chair or rotating action about the transverse axis through the vehicle parallel to ground. Due to pitching, the front suspension moves out of phase with the rear resulting in rocking effect in a vehicle.