Interpolate different sets of data using the same interval

Hello everyone,

I'm working on an university project in CFD, basically i have a fluid flowing in a pipe, i need to verify that the solution of the simulation in Fluent is mesh independent, so i have 3 type of grid, the raw one, medium and the finest one. I plot the velocity values along the axis and i must compare the results in 3 cases (if the root mean square is < then 2%, it's ok). My problem is, since the finest mesh have more cells then the medium one etc, I have more values for the finest mesh on the same interval.

Like:

raw mesh x = 0 --> y = 1 x = 0,5 --> y = 1,2

medium mesh x = 0 --> y = 1 x = 0,1 --> y = 1 x = 0,2 --> y = 1,01 x = 0,3 --> y = 1,05 x = 0,4 --> y = 1,1 x = 0,5 --> y = 1,2

I need to have a fixed number of points for X, (50 points for example) and have the Y values associated to be able to compare the 3 different cases.

I think it can be done with interp1 function but i'm not really sure how to do that, i hope someone can help me, thank you in advance.

Regards, Vlad.

Answer 1

[Martin Schätz]

Hi, as you said you can use interp1 function. You will have the raw mesh like this:

x = 0:1:10; %step by 1
v = sin(x);

with smaller step.

figure
plot(x,v,'o');
title('Original Data');

To interpolate data, you have to create new variable with smaller steps (now is the step 0.1 as u want for your medium mesh).

xq = 0:0.1:10; % new step by 0.1
vq1 = interp1(x,v,xq,'spline');

Then after interpolation, you will get data with smaller step.

figure
plot(xq,vq1,'o');
title('(Default) Linear Interpolation');

You can easily use this code, but look at the help for interp1 and choose right interpolation method for your data.