DETERMINATION OF AIR DRAG COEFFICIENT OF VEHICLE MODELS
INTRODUCTION
- The early 1970s were characterised with shortage of fuels intended for powering of motor vehicles.this fact had been the main reason why car manufacturers were stated to find solutions in order to reduce fuel consumption .
- At that time the only possible way to reduce fuel consumption is reducing drags due to vehicle rolling process and air flows around the vehicle.
- since drag to vehicle rolling process is directly connected with the mass of the vehicle and rolling coefficient.
- today,modern vehicles mostly use highways an acheive very high speeds,where a dominate drag to vehicle motion becomes the air drag .A right solution to reduce air drag of modern motor vehicle is additional designing every outside element of the vehicle body. Research on vehicle design and every outside element of the vehicle body based on experimental set up. one of the experimental set of includes wind tunnel experiment.
VEHICLE MODEL AND EXPERIMENTAL SETUP
the every step of experiment is challenge like eliminating influence of air rolling process and achieving stationary conditions.measuring of small forcesexactly due to airdrag .a vehicle model is placed on a glass surface that is placed in the centre of the wind tonnel nozzle.an elimination of rolling it was levered by strain gauges.
Finally,it was necessary to measure very small values of air drags and solution for the air drag problem is strain guages.
DETERMINATION OF DRAG COEFFICIENT
An object for researching model of car,GT type in the ratio of 1:18.Having in mind the basic dimensions of the vehicle model,frontal area A = 57.88 cm^2 was calculated ,since experiment will give an answer on values of air drags "F" ,and knowing of airdensity "rho" aas well as velocity of air flow v,the drag coefficient c_d of the vehicle model can be calculated by following expression
the c_d calculated by following expression
c_d = F*2/rho*A*v^2
Measurements of air drags were conducted for different air speeds during increasing and decreasing velocity of air flows. However, it is very important to notice that values of air drags were collected during keeping constant air speed.
THE MATLAB PRORAM IS
% determination of air drag coefficients
% inputs
A = 56.81;
F = 1.5;
% air density
rho = 1.225;
v = linspace(50,150,11);
V = linspace(150,50,11);
term1 = rho*A*v.^2;
term2 = rho*A*V.^2;
c_d = F*2./term1;
c_d1 = F*2./term2;
hold on
plot(v,c_d,'color','r');
plot(V,c_d,'color','b');
xlabel('Airsped(in km/h)');
ylabel('dragcoefficient');
grid on
CONCLUSION
In order to achieve good results it is recommended to select a right vehicle model in proper ratio,that is directly connected to the frontal area of the vehicle model and air drag(forces)produced by the air flow.
this method could be very useful for determination of air drag coefficient of some parts of vehicle body and it could be recommended in early phase of design