Trying to plot specific values from a vector

Hi, I am trying to plot the TSFC values and Pcr values for specfic values of To4 which are 1500,1600, and 1700. So that I will end up with three lines. How could I do this?

Answer 1

[Mathieu NOE]

hello

this is my suggestion - I put the equations in a sub function to make it easy after to do a for loop for multiple To4 values

also changes the Pcr from linspace to logspace vector as it seems to better render in the semilogx plot (my opinion)

clc
clearvars

% 
%Turbojet - Rolls Royce Olympus 593
%Range = 6440 km
%Engine Weight = 3386 kg;
%Ramjet is based off the Blackbird SR-71

%% Takeoff TJ
Pa = 101325; % in Pa
Pe = Pa;
rho = 1.225; %kg/m^3
Ai = 0.4902; %inlet area in meters
ma = 64.4; %mass flow rate in kg/s
u = ma/(rho*Ai);
h = 0; %km 
T = 169000; % Thrust in N
R = 287; %J/kg*K
Ta = 288.15; % ambient temperature at Sea Level
gamma = 1.4;


Pcr = logspace(0,2,25);
To4 = [1500;1600;1700];

for ci = 1:length(To4)
    TSFC(ci,:) = mysubfn1(Pcr,u,gamma,R,Ta,Pa,ma,T,To4(ci))
    leg_str{ci} = ['To4 = ' num2str(To4(ci))];
end

semilogx(Pcr,TSFC)
legend(leg_str);

function [TSFC] = mysubfn1(Pcr,u,gamma,R,Ta,Pa,ma,T,To4)

    M = u/sqrt(gamma*R*Ta);
    %compressor inlet conditions
    To2 = Ta*(1+((gamma-1)/2)*M^2);
    yd = 1.4;
    nd = 0.97;
    Po2 = Pa*(1+nd*((To2/Ta)-1))^(yd/(yd-1));
    % Pcr = linspace(0,100,10);
    % To4 = linspace(1500,1700,10);
    Po3 = Po2.*Pcr;
    yc = 1.37;
    nc = 0.85;
    To3 = To2.*(1+(1./nc).*(Pcr.^((yc-1)./yc))-1);  
    Q = 45000000; %heating value in K/kg
    Cp = 1000; %J/kgK
    f = ((To4./To3)-1)./(((Q.*To3)./Cp)-To4./To3);
    Po4 = Po3;
    To5 = To4-(To3-To2);
    nt = 0.90;
    yt =1.33;
    Po5 = Po4.*(1-(1/nt).*(1-(To5./To4))).^(yt/(yt-1));
    %nozzle conditions with no afterburner
    To6 = To5;
    Po6 = Po5;
    yn = 1.36;
    nn = 0.98;
    ue = sqrt(2.*nn.*(yn./(yn-1)).*R.*To6.*(1-(Pa./Po6).^(yn-1)./yn));
    mf = f.*ma;
    TSFC = mf./T;

end

[Caroline Kenemer]

When I try to put that in each section and run the individual sections it gives an error for the sections below the section I'm running because those statements are above the function (even though I'm not running that section)

[Caroline Kenemer]

also how would I add an xlabel, ylabel, and title

[Caroline Kenemer]

nvm on the last two comments but how would i make Pcr from 0 to 100 in increments of 10

[Mathieu NOE]

hello again

1/ if you have multiple functions in one code , the functions must always be at the very end of the code, all "main" code must be written in the upper section; you can have multiple functions , simply make sure they have individual names

2/ xlabel, ylabel, and title : it's exactly this way to code it :

semilogx(Pcr,TSFC)
title('TSFC vs. Pcr vs. To4')
legend(leg_str);
xlabel('Pcr')
ylabel('TSFC') 

3/ sure, you can always get back to linspace

or this way : Pcr = (0:10:100);

did you notice that Pcr = 0 will issue a NaN result because you make a division by zero in this line :

f = ((To4./To3)-1)./(((Q.*To3)./Cp)-To4./To3);

I send back the full code :

clc
clearvars
% 
%Turbojet - Rolls Royce Olympus 593
%Range = 6440 km
%Engine Weight = 3386 kg;
%Ramjet is based off the Blackbird SR-71
%% Takeoff TJ
Pa = 101325; % in Pa
Pe = Pa;
rho = 1.225; %kg/m^3
Ai = 0.4902; %inlet area in meters
ma = 64.4; %mass flow rate in kg/s
u = ma/(rho*Ai);
h = 0; %km 
T = 169000; % Thrust in N
R = 287; %J/kg*K
Ta = 288.15; % ambient temperature at Sea Level
gamma = 1.4;

% Pcr = logspace(0,2,25);
Pcr = (0:10:100);

To4 = [1500;1600;1700];
for ci = 1:length(To4)
    TSFC(ci,:) = mysubfn1(Pcr,u,gamma,R,Ta,Pa,ma,T,To4(ci))
    leg_str{ci} = ['To4 = ' num2str(To4(ci))];
end
figure(1),
plot(Pcr,TSFC)
title('TSFC vs. Pcr vs. To4')
legend(leg_str);
xlabel('Pcr')
ylabel('TSFC')


function [TSFC] = mysubfn1(Pcr,u,gamma,R,Ta,Pa,ma,T,To4)
    M = u/sqrt(gamma*R*Ta);
    %compressor inlet conditions
    To2 = Ta*(1+((gamma-1)/2)*M^2);
    yd = 1.4;
    nd = 0.97;
    Po2 = Pa*(1+nd*((To2/Ta)-1))^(yd/(yd-1));
    % Pcr = linspace(0,100,10);
    % To4 = linspace(1500,1700,10);
    Po3 = Po2.*Pcr;
    yc = 1.37;
    nc = 0.85;
    To3 = To2.*(1+(1./nc).*(Pcr.^((yc-1)./yc))-1);  
    Q = 45000000; %heating value in K/kg
    Cp = 1000; %J/kgK
    f = ((To4./To3)-1)./(((Q.*To3)./Cp)-To4./To3);
    Po4 = Po3;
    To5 = To4-(To3-To2);
    nt = 0.90;
    yt =1.33;
    Po5 = Po4.*(1-(1/nt).*(1-(To5./To4))).^(yt/(yt-1));
    %nozzle conditions with no afterburner
    To6 = To5;
    Po6 = Po5;
    yn = 1.36;
    nn = 0.98;
    ue = sqrt(2.*nn.*(yn./(yn-1)).*R.*To6.*(1-(Pa./Po6).^(yn-1)./yn));
    mf = f.*ma;
    TSFC = mf./T;
end