DRAG FORCE

DRAG FORCE

 

DRAG FORCE:

Drag force is a force,which resistance offered by the fluid like air or water.if we consider a car travelling a point A to B,we put a hand outside thorugh the window,then we feel the opposive of air.its known as drag force.

 

DRAG FORCE EQUATION:

When the drag takes place in the presence of air, it is known as aerodynamic drag. When it takes place in water, it is known as hydrodynamic drag.

 

F_D = ½c_dρAv²

 

Where,

C_d-Drag co-efficient,which is dimensionless with value,depending upon the shape of object.(c_d=0.33-0.41 for mini cars and c_d=0.31-0.40 for sport cars etc...).

ρ -rho is the density of fluid.

V – velocity of the object.

A – cross sectional area of object( In automonile 'A' consider as frontal area).

UNIT OF DRAG FORCE:NEWTON or N

Drag force is propotional to the square of the velocity.if the velocity of speed increases two times,drag force increases four times.

EXAMPLE:

• A car travelling on a road.
• A bicycle pedalling on a road.
• Airplane moves one place to another.

TO CALCULATE DRAG FORCE USING MATLAB:

clear all
close all
clc
%flow over a bicycle

%input
%drag co efficient
c_d1=0.25;
c_d2=[0.33:0.05:0.46];
%area m^2
a=1.72;
%density kg/m^3
rho=1.2;
%velocity
v1=[0:50];
v2=[40];
drag_force1=rho*a*v1.^2*c_d1*0.5
drag_force2=rho*a*v2.^2*c_d2*0.5

%plot1 velocity and drag_force 
figure(1)
plot(v1,drag_force1)
xlabel('velocity','Color','b')
ylabel('drag force','Color','b')
title('comparision of drag force and velocity')
grid on

%plot2 c_d and drag force
figure(2)
plot(c_d2,drag_force2)
title('comparision of drag force and c_d')
xlabel('c_d','Color','b')
ylabel('drag force','Color','b')
grid on

 

OUTPUT:

 

PLOT VELOCITY VS DRAG FORCE:

PLOT DRAG CO-EFFICIENT VS DRAG FORCE: