MATLAB Matlab - plot pressure distribution around a circle

AI Thread Summary
The discussion focuses on plotting the pressure distribution around a cylinder in a uniform flow field using MATLAB. The user has the ideal pressure coefficient equation and is attempting to visualize it with a polar plot, but encounters issues because the plot starts at the origin instead of around the circle. They initially tried scaling the pressure coefficient by adding the cylinder's radius but found it ineffective. A suggested solution involves using a different scaling function to properly adjust the pressure coefficient for the plot. The user expresses appreciation for any assistance in resolving the plotting challenge.
super sky
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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

Uploaded with ImageShack.us

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
radius = sqrt(M/2/pi/U);    % Cylinder radius
t = linspace(0,2*pi,50);    % Range of theta values
circle = ones(1,50);        % Create vector
circle = radius.*circle;    % Circle of required radius

% 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:
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Pretty useless now,

just in case if you ever wonder what was missing

super sky said:
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

Uploaded with ImageShack.us

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
radius = sqrt(M/2/pi/U);    % Cylinder radius
t = linspace(0,2*pi,50);    % Range of theta values
circle = ones(1,50);        % Create vector
circle = radius.*circle;    % Circle of required radius

% Calculations
cp = 1 - 4.*(sin(t)).^2;     % Pressure coefficient
cp_scaled = sqrt(cp.^2 + circle.^2); % 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:
Thanks :)
I never did figure it out, so it was helpful to know in case I have to do it again.
 
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