# Matlab - plot pressure distribution around a circle

• MATLAB
super sky
I'm trying to plot the pressure distribution around a cylinder in a uniform flow field, so that the graphic is a circle with the pressure curve around it, like in the image below.
http://img843.imageshack.us/img843/4649/63792687.th.jpg [Broken]

I have the equation for the ideal pressure coefficient Cp (which is what I'm wanting to display), and t is the theta values. (See code below)

Then I use the polar function to plot it... polar(t,Cp)... but that starts at the origin, which isn't what I want. I thought it might help if I added the radius of my proposed circle to Cp, but it doesn't. So maybe I need a scaling factor on Cp or something..?

Could someone help me out?
Thanks.

Code:
%%% Flow Around a Cylinder %%%

% Initialise variables
clear all
clc

U = 12;     % Freestream velocity m/s
M = 2;      % Doublet strength
t = linspace(0,2*pi,50);    % Range of theta values
circle = ones(1,50);        % Create vector

% Calculations
cp = 1 - 4.*(sin(t)).^2;     % Pressure coefficient
cp_scaled = cp + radius;     % Attempted scaling

% Display graphs
polar(t,cp,'--r')
hold on
polar(t,circle)
hold off
figure
polar(t,cp_scaled,'--r')
hold on
polar(t,circle)
hold off

Last edited by a moderator:

wgh87
Pretty useless now,

just in case if you ever wonder what was missing

I'm trying to plot the pressure distribution around a cylinder in a uniform flow field, so that the graphic is a circle with the pressure curve around it, like in the image below.
http://img843.imageshack.us/img843/4649/63792687.th.jpg [Broken]

I have the equation for the ideal pressure coefficient Cp (which is what I'm wanting to display), and t is the theta values. (See code below)

Then I use the polar function to plot it... polar(t,Cp)... but that starts at the origin, which isn't what I want. I thought it might help if I added the radius of my proposed circle to Cp, but it doesn't. So maybe I need a scaling factor on Cp or something..?

Could someone help me out?
Thanks.

Code:
%%% Flow Around a Cylinder %%%

% Initialise variables
clear all
clc

U = 12;     % Freestream velocity m/s
M = 2;      % Doublet strength
t = linspace(0,2*pi,50);    % Range of theta values
circle = ones(1,50);        % Create vector

% Calculations
cp = 1 - 4.*(sin(t)).^2;     % Pressure coefficient
[COLOR="Red"]cp_scaled = sqrt(cp.^2 + circle.^2)[/COLOR]; % the missing function

% Display graphs
polar(t,cp,'--r')
hold on
polar(t,circle)
hold off
figure
polar(t,cp_scaled,'--r')
hold on
polar(t,circle)
hold off

Last edited by a moderator:
super sky
Thanks :)
I never did figure it out, so it was helpful to know in case I have to do it again.