recieving error while using atand command

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mehmet salihi
mehmet salihi 2021-12-26
评论： mehmet salihi 2021-12-27
Hi everyon,
when V0 <10 the code is working without problem.
but when V0 >= 10
Phi is giving NaN values and so a and a_prime are giving missing value.
could you please help me where is the error in my code, or why Phi is giving NaN
Please kindlly find the attachments for excel files also attched
clear all;
clc
%%% Fixed Parameters
B = 2; % Number of Blades
R = 10.06; % Blade Radius in meter
Rho = 1.225; % Density of air kg/m3
%V0 =10; % Wind Speed m/s I Have problem %when I recomment this line
V0 =5; % Wind Speed m/s
w = 7.501; % Rotational Speed rad/s
Theta_P = -3; % Tip Pitch Angle in degree
ac = 0.2; % Glauert correction
eps = 1.e-5; % Error tolerance
%%% Given Blade Data
ns=26;
sections = readmatrix('chord and twist variations.xlsx');
r=sections(:,2); % Radial Distance in meter
Chord=sections(:,4); % Chord length in meter
Beta=sections(:,5); % Twist in degree
%%% Airfoil Date
afoil = readmatrix('airfoil data.xlsx');
Aoa = afoil(:,1);
Cl = afoil(:,2);
Cd = afoil(:,3);
for i = 8:length(r)
sigma(i) = (B*Chord(i))/(2*pi*r(i));
a=0;
a_prime=0;
alist(i)=[0];
alistprime(i)=[0];
disp(['Section ',num2str(i)])
for n=1:1000
Phi = atand(((1-a)*V0)/((1+a_prime)*w*r(i))); % Flow Angle
Theta = Beta(i) + Theta_P ;
aoa = Phi- Theta; % local angle of attack in degree
f = (B/2)* ((R-r(i))/(r(i)*sind(Phi)));
F = (2/pi)*acos(exp(-f)); % Prandtl correction factor
cl=interp1(Aoa,Cl,aoa);
cd=interp1(Aoa,Cd,aoa);
Cn = cl*cosd(Phi)+cd*sind(Phi);
Ct =cl*sind(Phi)-cd*cosd(Phi);
K=(4*F*(sind(Phi))^2)/(sigma(i)*Cn);
%%%%%%%%%% a and ac condition
a = 1/(((4*F*(sind(Phi)^2))/(sigma(i)*Cn))+1);
if a < ac || a==ac
a=a;
else
a = 0.5*(2+K*(1-2*ac)-sqrt(((K*(1-2*ac)+2)^2)+4*((K*(ac^2))-1)));
end
a_prime =1/(((4*F*(sind(Phi)*cosd(Phi)))/(sigma(i)*Ct))-1);
alist(i,n+1)=a;
alistprime(i,n+1)=a_prime;
disp([" a ",a,' a_old ',alist(i,n)," a_prime ",a_prime,' a_Prime_old ',alistprime(i,n)])
%%% condition for epsilon or tolerance
if a-alist(i,n) < eps && a_prime-alistprime(i,n) < eps
break;
end
end
%%% V relative
v_rel(i) = sqrt( (V0*(1-alist(end)))^2 + (w*r(i)*(1+alistprime(end)))^2 );
%%% The tangential force per length Pt
Pt(i) = 0.5*Rho*(v_rel(i)^2)*Chord(i)*Ct;
end

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采纳的回答

Simon Chan
Simon Chan 2021-12-26
The value of variable 'aoa' is outside the interpolation range 'Aoa' and hence it gives NaN as the result.
So the root cause is not coming from Phi.
You may use extrapolation and select your method of doing that.
The following is using linear extrapolation as the method.
cl=interp1(Aoa,Cl,aoa,'linear','extrap');
cd=interp1(Aoa,Cd,aoa,'linear','extrap');

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