# Circle grid vs. Squared grid

Good Morning everybody,

I’ve already posted something like this,but probably I was not smart enough to describe what I meant.

By means of Matlab, I’m striving to get a code enabling me to engender a 3D turbulent wind field on a grid spotted in front of a wind turbine rotor.

So far I’ve been able to generate only a circled grid of points. The algorithm I used is the subsequent:

dpsi = 2*pi/np;
for i= 1:nc,
ric(i)= r1 + (i-1)*drc;
for k=1:np,
psiip(k) = (k-1)*dpsi;
j = (i-1)*np+k;
y((i-1)*np+k)= ric(i)*cos(psiip(k));
z((i-1)*np+k)= HubHt - ric(i)*sin(psiip(k));
end;
end;

where

• np : number of points on a circle;
• nc : number of circles;
• r1 : the most inner circle’s radius;
• drc : distance between to circles;
• y,z : point coordinates;
• HubHt : hub height;
• j : point index.

I know that a squared grid is incredibly more suited for big sized wind turbine,since interpolation is the major issue. Hence,I’d like to ask if anybody could give me some hints about how to get a squared grid of points,with or without the extra hub point.
I really look forward to getting an answer whenever possible.

Greetings from Italy,

Francesco Perrone

Francesco,

You may want to look at some of our source code. See TurbSim for how to generate the grid and to normalize the data to make storage and I/O efficient and look at AeroDyn to see how to read it and apply it to the turbine. You can find the source code in the archives of AeroDyn and TurbSim:

I think you will find that it’s much easier and faster to interpolate into a rectangular grid than a circular grid. The advantages of circular grids ended with the variable-speed, flexible turbine. With a fixed-speed, rigid, unyawed turbine, you can make it so the points in the turbulence grid always align with the analysis nodes (the grid rotates with the turbine). This eliminates interpolation smoothing, which reduces the effected turbulence intensity. This method is no longer realistic, so we switched to rectangular grids for computational efficiency.

Marshall