1function isentropic(g)
2% ISENTROPIC  isentropic, adiabatic flow example
3%
4%    In this example, the area ratio vs. Mach number curve is
5%    computed for a hydrogen/nitrogen gas mixture.
6%
7help isentropic
8
9if nargin == 1
10   gas = g;
11else
12   gas = Solution('gri30.yaml');
13end
14
15% set the stagnation state
16set(gas,'T',1200.0,'P',10.0*oneatm,'X','H2:1,N2:0.1');
17s0 = entropy_mass(gas);
18h0 = enthalpy_mass(gas);
19p0 = pressure(gas);
20
21mdot = 1;  % arbitrary
22
23mach = [];
24a = [];
25i = 1;
26amin = 1.e14;
27
28% compute values for a range of pressure ratios
29for r = 0.005:0.0025:0.995
30   p = p0*r;
31
32   % set the state using (p,s0)
33   set(gas,'P',p,'S',s0);
34
35   h = enthalpy_mass(gas);
36   rho = density(gas);
37
38   v2 = 2.0*(h0 - h);      %   h + V^2/2 = h0
39   v = sqrt(v2);
40   a(i) = mdot/(rho*v);    %   rho*v*A = constant
41
42   if a(i) < amin
43      amin = a(i);
44   end
45   mach(i) = v/soundspeed(gas);
46   i = i + 1;
47end
48
49a = a/amin;
50
51% plot results
52
53clf;
54plot(mach,a);
55ylabel('Area Ratio');
56xlabel('Mach Number');
57title('Isentropic Flow: Area Ratio vs. Mach Number');
58