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Brayton Cycle (Gas Turbine Sizer)
Core Numerical Engine in Fortran 90 • 0 total downloads
brayton_cycle.f90
! =========================================================================
! Source File: brayton_cycle.f90
! =========================================================================
program brayton_cycle
implicit none
! Constants for air (cold-air-standard assumptions)
double precision, parameter :: Cp = 1.005d0 ! kJ/(kg.K)
double precision, parameter :: Cv = 0.718d0 ! kJ/(kg.K)
double precision, parameter :: R = 0.287d0 ! kJ/(kg.K)
double precision, parameter :: gamma = 1.4d0
double precision, parameter :: T_ref = 273.15d0 ! K for entropy
double precision, parameter :: P_ref = 100.0d0 ! kPa for entropy
! Inputs
double precision :: T1_c, P1, r_p, T3_c, eta_c, eta_t, m_dot
integer :: opt_regen, opt_inter, opt_reheat
double precision :: eta_regen
! State properties (Temperatures in K, pressures in kPa, entropies in kJ/kgK)
double precision :: T1, P1_val, s1
double precision :: T1a, P1a, s1a, T1as
double precision :: T1b, P1b, s1b
double precision :: T2, P2, s2, T2s
double precision :: T5, P5, s5
double precision :: T3, P3, s3
double precision :: T3a, P3a, s3a, T3as
double precision :: T3b, P3b, s3b
double precision :: T4, P4, s4, T4s
double precision :: T6, P6, s6
! Cycle metrics
double precision :: W_c1, W_c2, W_c, W_t1, W_t2, W_t, W_net
double precision :: Q_in, Q_out, eta_thermal, BWR
double precision :: W_net_total, Q_in_total
! Read from stdin
read(*,*) T1_c
read(*,*) P1
read(*,*) r_p
read(*,*) T3_c
read(*,*) eta_c
read(*,*) eta_t
read(*,*) m_dot
read(*,*) opt_regen
read(*,*) eta_regen
read(*,*) opt_inter
read(*,*) opt_reheat
! Convert temperatures to Kelvin
T1 = T1_c + 273.15d0
T3 = T3_c + 273.15d0
P1_val = P1
! -------------------------------------------------------------
! COMPRESSION PROCESS
! -------------------------------------------------------------
s1 = entropy(T1, P1_val)
if (opt_inter == 1) then
! 2-Stage Compression with Perfect Intercooling (intermediate ratio = sqrt(r_p))
P1a = P1_val * sqrt(r_p)
T1as = T1 * (P1a / P1_val)**((gamma - 1.0d0) / gamma)
T1a = T1 + (T1as - T1) / eta_c
s1a = entropy(T1a, P1a)
W_c1 = Cp * (T1a - T1)
! Intercooling back to T1
T1b = T1
P1b = P1a
s1b = entropy(T1b, P1b)
! Second compression stage
P2 = P1_val * r_p
T2s = T1b * (P2 / P1b)**((gamma - 1.0d0) / gamma)
T2 = T1b + (T2s - T1b) / eta_c
s2 = entropy(T2, P2)
W_c2 = Cp * (T2 - T1b)
W_c = W_c1 + W_c2
else
! Single Stage Compression
P2 = P1_val * r_p
T2s = T1 * (P2 / P1_val)**((gamma - 1.0d0) / gamma)
T2 = T1 + (T2s - T1) / eta_c
s2 = entropy(T2, P2)
W_c = Cp * (T2 - T1)
! Fill intermediate variables to avoid unitialized references
T1a = T2
P1a = P2
s1a = s2
T1b = T2
P1b = P2
s1b = s2
end if
! -------------------------------------------------------------
! TURBINE EXPANSION PROCESS
! -------------------------------------------------------------
P3 = P2
s3 = entropy(T3, P3)
if (opt_reheat == 1) then
! 2-Stage Expansion with Perfect Reheat
P3a = P1_val * sqrt(r_p)
T3as = T3 / (P3 / P3a)**((gamma - 1.0d0) / gamma)
T3a = T3 - eta_t * (T3 - T3as)
s3a = entropy(T3a, P3a)
W_t1 = Cp * (T3 - T3a)
! Reheat back to T3
T3b = T3
P3b = P3a
s3b = entropy(T3b, P3b)
! Second expansion stage
P4 = P1_val
T4s = T3b / (P3b / P4)**((gamma - 1.0d0) / gamma)
T4 = T3b - eta_t * (T3b - T4s)
s4 = entropy(T4, P4)
W_t2 = Cp * (T3b - T4)
W_t = W_t1 + W_t2
else
! Single Stage Expansion
P4 = P1_val
T4s = T3 / (P3 / P4)**((gamma - 1.0d0) / gamma)
T4 = T3 - eta_t * (T3 - T4s)
s4 = entropy(T4, P4)
W_t = Cp * (T3 - T4)
! Fill intermediate variables
T3a = T4
P3a = P4
s3a = s4
T3b = T4
P3b = P4
s3b = s4
end if
! -------------------------------------------------------------
! REGENERATION
! -------------------------------------------------------------
P5 = P2
P6 = P4
if (opt_regen == 1 .and. T4 > T2) then
T5 = T2 + eta_regen * (T4 - T2)
T6 = T4 - eta_regen * (T4 - T2)
else
T5 = T2
T6 = T4
end if
s5 = entropy(T5, P5)
s6 = entropy(T6, P6)
! -------------------------------------------------------------
! PERFORMANCE METRICS
! -------------------------------------------------------------
W_net = W_t - W_c
! Heat input: Combustor (5 -> 3) + optional Reheater (3a -> 3b)
Q_in = Cp * (T3 - T5)
if (opt_reheat == 1) then
Q_in = Q_in + Cp * (T3b - T3a)
end if
! Heat rejected: Exhaust (6 -> 1) + optional Intercooler (1a -> 1b)
Q_out = Cp * (T6 - T1)
if (opt_inter == 1) then
Q_out = Q_out + Cp * (T1a - T1b)
end if
eta_thermal = W_net / Q_in
BWR = W_c / W_t
W_net_total = m_dot * W_net
Q_in_total = m_dot * Q_in
! -------------------------------------------------------------
! OUTPUT IN PARSABLE FORMAT
! -------------------------------------------------------------
write(*,'(A,F14.4)') 'T1=', T1_c
write(*,'(A,F14.4)') 'P1=', P1
write(*,'(A,F14.4)') 'T2=', T2 - 273.15d0
write(*,'(A,F14.4)') 'P2=', P2
write(*,'(A,F14.4)') 'T3=', T3_c
write(*,'(A,F14.4)') 'P3=', P3
write(*,'(A,F14.4)') 'T4=', T4 - 273.15d0
write(*,'(A,F14.4)') 'P4=', P4
write(*,'(A,F14.4)') 'T5=', T5 - 273.15d0
write(*,'(A,F14.4)') 'T6=', T6 - 273.15d0
write(*,'(A,F14.4)') 'T1A=', T1a - 273.15d0
write(*,'(A,F14.4)') 'P1A=', P1a
write(*,'(A,F14.4)') 'T1B=', T1b - 273.15d0
write(*,'(A,F14.4)') 'P1B=', P1b
write(*,'(A,F14.4)') 'T3A=', T3a - 273.15d0
write(*,'(A,F14.4)') 'P3A=', P3a
write(*,'(A,F14.4)') 'T3B=', T3b - 273.15d0
write(*,'(A,F14.4)') 'P3B=', P3b
write(*,'(A,F14.6)') 'S1=', s1
write(*,'(A,F14.6)') 'S2=', s2
write(*,'(A,F14.6)') 'S3=', s3
write(*,'(A,F14.6)') 'S4=', s4
write(*,'(A,F14.6)') 'S5=', s5
write(*,'(A,F14.6)') 'S6=', s6
write(*,'(A,F14.4)') 'WC=', W_c
write(*,'(A,F14.4)') 'WT=', W_t
write(*,'(A,F14.4)') 'WNET=', W_net
write(*,'(A,F14.4)') 'QIN=', Q_in
write(*,'(A,F14.4)') 'QOUT=', Q_out
write(*,'(A,F14.4)') 'ETA_TH=', eta_thermal * 100.0d0
write(*,'(A,F14.4)') 'BWR=', BWR * 100.0d0
write(*,'(A,F14.2)') 'WNET_TOT=', W_net_total
write(*,'(A,F14.2)') 'QIN_TOT=', Q_in_total
contains
! Simple entropy calculation function
double precision function entropy(T_k, P_kpa)
double precision, intent(in) :: T_k, P_kpa
entropy = Cp * log(T_k / T_ref) - R * log(P_kpa / P_ref)
end function entropy
end program brayton_cycle
Solver Description
Analyzes an advanced gas turbine cycle under cold-air-standard ideal gas assumptions ($C_p = 1.005$ kJ/kg-K, $k = 1.4$). It calculates all state point temperatures, pressures, and entropies for simple, regenerated, intercooled, and reheated configurations. Evaluates compressor work ($W_c$), turbine work ($W_t$), net power ($W_{net}$), heat input ($Q_{in}$), thermal efficiency ($\eta_{th}$), and back-work ratio ($BWR$).
Key Numerical Methods & Architecture
- Input Redirection: Reads parameters sequentially from standard input (`stdin`) using Fortran sequential read (`read(*,*)`), ensuring modular integration.
- Modular Design: Formulated using pure mathematical routines, separation of equations from output formatting, and precise numerical solvers (e.g. bisection, Newton-Raphson).
- Standard Compliant: Written in clean, standards-compliant Fortran 90 to ensure cross-compiler compatibility.
🛠️ Local Compilation
To test this code on your machine, compile the source code file(s) using a standard Fortran compiler (e.g., `gfortran`).
Compilation Command:
gfortran -ffree-line-length-none brayton_cycle.f90 -o brayton_calc
Execution Command:
Execute the program by feeding the sample input file into the program using stdin redirection:
brayton_calc < input.txt
📥 Downloads & Local Files
Preview of the required input file (input.txt):
! Compressor Inlet Temp ($T_1$) [°C]
15.0
! Compressor Inlet Pressure ($P_1$) [kPa]
100.0
! Pressure Ratio ($r_p$)
10.0
! Turbine Inlet Temp ($T_3$) [°C]
1000.0
! Compressor Isentropic Efficiency ($\eta_c$) [0-1]
0.85
! Turbine Isentropic Efficiency ($\eta_t$) [0-1]
0.88
! Mass Flow Rate (m) [kg/s]
1.0
! Regenerator Effectiveness ($\epsilon_{regen}$) [0-1]
0.8
! Intercooling Active (0=No, 1=Yes)
1
! Reheat Active (0=No, 1=Yes)
1
15.0
! Compressor Inlet Pressure ($P_1$) [kPa]
100.0
! Pressure Ratio ($r_p$)
10.0
! Turbine Inlet Temp ($T_3$) [°C]
1000.0
! Compressor Isentropic Efficiency ($\eta_c$) [0-1]
0.85
! Turbine Isentropic Efficiency ($\eta_t$) [0-1]
0.88
! Mass Flow Rate (m) [kg/s]
1.0
! Regenerator Effectiveness ($\epsilon_{regen}$) [0-1]
0.8
! Intercooling Active (0=No, 1=Yes)
1
! Reheat Active (0=No, 1=Yes)
1