# Vehicle Aerodynamics | Reducing Drag On A Car

## What makes a vehicle aerodynamics?

Vehicle Aerodynamics is a potential area to minimize the fuel consumption. Because the air drag acting on the vehicle is directly proportional to the square of the vehicle speed. So by thoroughly studying and by providing necessary modification the drag force is reduced and there by the following advantages can be achieved.

• Minimum speed and acceleration for the same power output
• Fuel consumption is reduced, about 35 % of the fuel cost can be reduced by proper stream lining
• Good appearance
• By reducing the various forces and moments, good stability and safety can be achieved

## Study of Vehicle Aerodynamics

The study of aerodynamics is carried out in two stages as follows:

• Making a solid model of the car to suitable scale for wind tunnel testing for body exterior optimisation
• By conducting a road test to check the drag co-efficient

## Reynolds Model Law

Here the model is made according to the calculation done by the Reynolds model law:

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If viscous forces alone are predominant, a model, may be taken to be dynamically similar to the prototype if the ratio of the inertial to the viscous forces is the same in the model and the prototype.

Re = ρVL/μ

The law in which models are based on Reynold’s Number is called as Reynold’s Model Law.

(Re)prototype  =  (Re)mode
ρp Vp LP / μp  =  ρm Vm Lm / μm
ρp Vp LP / ρm Vm Lm  . 1/ μp / μm = 1
ρr Vr Lr / μr = 1

Where scale ratio are
ρr = ρp / ρ’  Vr  =  Vp / Vm
Lr =  Lp / Lm,  μr = μp / μm

Now, Time scale ratio Tr = Lr / Vr

Velocity scale ratio Vr  =  Vr / Lr

Acceleration scale ratio ar  =  V

Force scale ratio
Fr  =  mr ar =  (ρr ArLr) ar
Fr =  (ρr L3r)ar

Discharge scale ratio
Qr =  ρr Ar Vr
Qr =  ρr Lr2 Vr