When i run the code, i dont see any plot, and i'm not sure why?

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Aeshasvi Bhajan
Aeshasvi Bhajan 2022-4-25
回答： Chunru 2022-4-26
figure;
plot(X,del,'color',[0.9290, 0.6940, 0.1250],'linewidth',1.5);
xlabel('Length of Plate (m)','FontSize', 12);
ylabel(' \delta in meter','FontSize', 12);
grid on;
set(gca,'FontSize',16);
title('Velocity boundary layer thickness','FontSize', 12);
  9 个评论
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Mathieu NOE
Mathieu NOE 2022-4-25
I don't have the Symb. toolbox (that's why I asked for a mat file)
I will let someone else answer this post
Rik
Rik 2022-4-25
That is not a mat file, that is an m-file. Rule of thumb: if you can run it in the online enviroment, your code is enough for us to debug the problem.

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回答（2 个）

Sam Chak
Sam Chak 2022-4-25
Hi @Aeshasvi Bhajan
If you insert this line:
increment = 0;
before this:
m = 0.5 + increment; % Units are in SI
then you can see the plots.
Chunru
Chunru 2022-4-26
Ran in:
syms x;
increment = 0.0;
m=0.5+increment; %Units are in SI
Pr=0.718; %Prandtl number
rho=1.204;%Air density at 20°C in SI (kg/m^3)
Tinf=293; %Entering air temperature at T0 (K)
k=0.0254; %Thermal conductivity (W/m-K)
Mu=1.825*10^-5; %Dynamic Viscosity (kg/m-s)
U0=30; %Velocity of Air (m/s)
U=U0.* (1 + x.^(0.2));
%% BOUNDARY LAYER'S VELOCITTY
dU_dx=diff(U,x);
del2_sq=((0.470*Mu)/(rho*(U^6)))*int(U^5,x,0,x);
fdel2_sq=matlabFunction(del2_sq);
K=(U*rho/Mu)*del2_sq*dU_dx;
fK=matlabFunction(K);
x=0:0.001:0.09;
for i=1:length(x) % to get numerical values
Num_K(i)=fK(x(i));
Num_del2_sq(i)=fdel2_sq(x(i));
end
for i=2:length(x)
eq=[1/82301184 1/4286520 -59/2381400 -74/297675 +1369/99225 -Num_K(i)];
sol=roots(eq);
lambda(i)=real(sol(5)); %real root only
end
Num_K(isnan(Num_K))=0;
Num_del2_sq(isnan(Num_del2_sq))=0;
del_sq = Num_del2_sq.*(lambda./Num_K);
del_sq = Num_del2_sq;
del = sqrt(del_sq); %velocity BL thickness
del(isnan(del))=0;
%% TEMPERATURE(THERMAL) BOUNDARY LAYER
Num_U=U0.* (1 + x.^(0.2)); %numerical_velocity U(x)
syms x zt zeta
Hzt1=@(zt) (zt^4/180) - ((3*zt^3)/140) + ((2*zt)/15);
Hzt2=@(zt) 2/(15*zt^2) - 3/(10*zt) - 3/(140*zt^4) + 1/(180*zt^5) +3/10;
fun1=(rho/Mu)*(Num_U.^2).*del_sq;
X=0:0.001:0.09;
C= [0.01 0.03 0.04 0.06];
for j=1:4
%%%%%%%%solving for zeta(iterative method)
start=(1+(C(j)/0.001));
zeta=zeros(); %initialize
zt=0.9; %%initial assumption
for i=start:91 %x is divided by 91 discrete points
fun=(4/Pr)*(int(U,x,C(j),x)/fun1(i));
fun_x=matlabFunction(fun);
for iteration=1:15 %it will converge to a value
if zt<=1
Hzt=Hzt1(zt); % uses first H(zt)
else
Hzt=Hzt2(zt); % uses second H(zt)
end
zt =real(sqrt(fun_x(X(i))/Hzt));
zt(isnan(zt))=0;
end
zeta(i)=zt;
end
del_t(:,j)=zeta.*del;
end
%% MAXIMUM TEMPERATURE DISTRIBUTION
Qw1=10000; %Heat Flux (W/m^2) %getting heat
T1=real((Qw1.*del_t(:,1)./(2*k))); %max temperature near wall
Qw2=-Qw1; %releasing heat
T2=real((Qw2*del_t(:,2)./(2*k))); %max temperature near wall
Qw3=5000; %Heat Flux (W/m^2) %releasing heat
T3=real((Qw3*del_t(:,3)/(2*k))); %max temperature near wall
Qw4=-Qw3; %releasing heat
T4=real((Qw4*del_t(:,4)/(2*k))); %max temperature near wall
T=real((T1+T2+T3+T4+Tinf)); %Maximum Temperature near wall in(K)
%Velocity, Thermal Boundary Layer and Temperature Distribution plots
if m==0.5 %plot when m=1/2
figure, plot(X,del,'color',[0.9290, 0.6940, 0.1250],'linewidth',1.5);
xlabel('Length of Plate (m)','FontSize', 12);
ylabel(' \delta in meter','FontSize', 12); grid on;
set(gca,'FontSize',16);
title('Velocity boundary layer thickness','FontSize', 12);
for i=1:4
figure, plot(X,del,'color',[ 0.47 0.25 0.80],'linewidth',1.5); hold on;
plot(X,del_t(:,i),'color',[ 0.25 0.80 0.54],'linewidth',1.5); hold on;
xlabel('Length of Plate (m)','FontSize', 12);
ylabel('\delta(m) and \delta_t (m)','FontSize', 16); grid on;
legend('\delta(m) velocity layer','\delta_t(m) Thermallayer','FontSize', 12, 'Location', 'SouthEast')
set(gca,'FontSize',16);
title(['Thermal boundary layer thickness at',num2str(C(i),3),'(m)'],'FontSize', 12);
hold off;
end
figure, plot(X,T,'b','linewidth',1.5);
xlabel('Length of Plate (m)','FontSize', 12);
ylabel('Temprature (K)','FontSize', 16); grid on;
set(gca,'FontSize',16);
title(['Max temprature plot for m = ',num2str(m,3)],'FontSize',12);
end

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