CALCULATING DRAG FORCE OF A MOVING OBJECT USING MATLAB

CALCULATING DRAG FORCE FOR FLOW OVER BICYCLE

AIM: To calculate drag force.

OBJECTIVE:

1. To execute a program for plotting velocity v/s dragforce.

2. To execute a program to plotting co-efficient of drag v/s dragforce.

FORMULE:

`Fd = 1/2 .rho.A.V^2.Cd`

Where,

Fd = Drag force, (N)

A = Frontal area of the moving object, (m^2)

V = Velocity of the moving object, (m/s)

rho = Density of fluid that object is resisting, (Kg/m^3)

Cd = Drag co-efficient, (Dimensionless quantity)

(Drag co-efficient is used to quantify the drag or resistance of an object in a fluid environment like air or water)

THEORY:

Drag is a fluid resistance or force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This exist between a fluid and a solid surface.

Drag force is proportional to the velocity for a laminar flow and the squared velocity for a turbulent flow.

Even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity.

Unlike other resistive forces, such as dry friction, which are nearly independent of velocity, but drag forces depend on velocity.

1.PROGRAM FOR PLOTTING VELOCITY V/S DRAG FORCE

% A program to calculate the drag force over a bicycle
clear all
close all
clc

% Inputs
% Drag co-efficient
c_d = [0.04]

% Area m^2
A = 0.1

% Density Kg/m^3
rho = 1.2

% velocity m/s
v = [1:60]

drag_force = rho*A*v.^2*c_d*0.5;

plot(v,drag_force)
xlabel('velocity')
ylabel('drag_force')
grid on

Here in the above program drag co-efficient is kept constant and value of velocity is varied.

PROGRAM OUTPUT

FIG:1

2.PROGRAM FOR PLOTTING DRAG CO-EFFICIENT V/S DRAG FORCE

% A program to calculate the drag force over a bicycle
clear all
close all
clc

% inputs
% Area m^2
A = 0.1

% Density Kg/m^3
rho = 1.2

% velocity m/s
v = 20

% Drag co-efficient of different shapes
c_d = [0.04 0.09 0.47 0.50 1.15]


drag_force = rho*A*v.^2*c_d*0.5;

plot(c_d,drag_force)
xlabel('drag_co-efficient')
ylabel('drag_force')
grid on

RESULTS AND CONCLUSION:

1. VELOCITY V/S DRAG FORCE:

As per the output in FIG-1 ( graph of velocity v/s drag force) , the plotted graph is parabolic because drag force on the object is directly praportional to the square of velocity of the moving object.

2. DRAG CO-EFFICIENT V/S DRAG FORCE:

As per the output in FIG-2 ( graph of drag co-efficient v/s drag force) ,the plotted graph is increasing linearly because drag co-efficient is directly praportional to drag force of the object moving.