Blade Element Calculations - Small Wind Turbines: Analysis, Design, and Application - page 84

Beside the inclusion of the tip loss and the new method of calculating a and a 0
based on Eqs. 5.7 , the changes from simple_power_calc.m are mainly to input
tabulated aerofoil data. The line
ReadIn 4412 % Read in Cl and Cd for the NACA 4412 section
%ReadIn 7062 % Read in Cl and Cd for the SD7062 section
is the only line specific to individual aerofoil sections.
The number of iterations per blade element is limited to 40. It has been
found that occasionally the calculations for the first element will not converge.
Usually this element contributes an insignificant amount to the power (as will
be shown below) so the problem is not a major one in practice. However, it is
important that the user take note of the output number of iterations when
running the program to tell whether the calculations have failed to converge for
any blade element.
Thestartofthedatafile naca4412.in is shown below. The first column is
a in degrees, the second is C l and the third C d . The data down to a = 12.0 is
for the lowest Re = 4.2 9 10 4 ,seeFig. 5.1 , and the first line of the data
(a =-3.0) is shown for the next Re of 8.3 9 10 4 . The rest of the file has
data similarly ordered. Obviously a new aerofoil would require a new data
file.