Turbojet Example

This example demonstrates how to use flight-mech to compute the characteristics of a turbojet.

Imports

# Python imports
import os
import sys
sys.path.append("..")

# Additional imports
import numpy as np
import matplotlib.pyplot as plt

# Flight-Mech imports
from flight_mech.turbine import TurbojetSingleBody

Turbojet definition

You first need to define the turbojet with its essential quantities.

# Define the turbojet
turbojet = TurbojetSingleBody()

# Set the design inputs
turbojet.compressor_efficiency = 0.86
turbojet.turbine_efficiency = 0.9
turbojet.OPR_design = 10
turbojet.T4_max = 1700  # K

Additionally, you need to set operating conditions.

# Set the operating conditions
turbojet.M0 = 0
turbojet.ambient_pressure = 101325  # Pa
turbojet.ambient_temperature = 285  # K

Design mode

The turbojet includes two modes, one for which the surface A4* will be considered as a variable and tuned to obtain a desired force. This mode is called the design mode.

We can now tune its value to obtain the desired thrust, here 7500 N.

# Tune A4* to obtain 7500N of thrust
turbojet.tune_A4_star_for_desired_thrust(7500)
print("A4* at 7500N [m2]:", turbojet.A4_star)

A4* at 7500N [m2]: 0.00813621917724611

Operation mode

Once the turbojet has been designed, you can switch to the operation mode. This mode allows you to compute the thrust and other quantities of the turbojet in a user-defined configuration.

First let us define the operation conditions and change the mode.

# Define the flight characteristics
cruise_altitude = 11800  # m
cruise_mach = 0.78
max_mach = 0.82
max_altitude = 12500  # m

# Switch to operation mode
turbojet.mode = "operation"

# Set the number of points for the plots
nb_points = 100

T4 influence

We can now for instance see the influence of a variation of T4 on the thrust. This roughly corresponds to changing the position of the throttle lever.

turbojet.T4_instruction=800
turbojet.tune_current_OPR()
turbojet.current_OPR

np.float64(3.565578125000005)

# Compute thrust evolution with T4 instruction
T4_array = np.linspace(800, turbojet.T4_max, nb_points)
thrust_array = np.zeros(nb_points)
for i, T4 in enumerate(T4_array):
    turbojet.T4_instruction = T4
    # Use try block to avoid crash if temperatures become negative
    try:
        turbojet.tune_current_OPR()
        thrust_array[i] = turbojet.thrust
    except Exception as e:
        print(e)

# Plot thrust evolution with velocity
plt.plot(T4_array, thrust_array)
plt.xlabel("T4 [K]")
plt.ylabel("Thrust [N]")
plt.title("Thrust evolution with T4")
plt.show()

Cruise

Let us now check the thrust obtained in cruise conditions.

# Switch to cruise conditions
# T4 not realistic but to see what happens at full power
turbojet.T4_instruction = turbojet.T4_max
turbojet.altitude = cruise_altitude
turbojet.M0 = cruise_mach

# Compute thrust in cruise
turbojet.tune_current_OPR()
print("cruise thrust [N]:", turbojet.thrust)

cruise thrust [N]: 2527.981038576462

Velocity influence

The velocity also has an influence on the thrust of the engine.

# Compute thrust evolution with velocity
mach_array = np.linspace(0, max_mach, nb_points)
thrust_array = np.zeros(nb_points)
for i, mach in enumerate(mach_array):
    turbojet.M0 = mach
    turbojet.tune_current_OPR()
    thrust_array[i] = turbojet.thrust

# Plot thrust evolution with velocity
plt.plot(mach_array, thrust_array)
plt.xlabel("M0")
plt.ylabel("Thrust [N]")
plt.title("Thrust evolution with Mach")
plt.show()

Altitude influence

The altitude also has an influence on the thrust of the engine.

# Compute thrust evolution with altitude
turbojet.M0 = cruise_mach
altitude_array = np.linspace(0, max_altitude, nb_points)
thrust_array = np.zeros(nb_points)
for i, altitude in enumerate(altitude_array):
    turbojet.altitude = altitude
    turbojet.tune_current_OPR()
    thrust_array[i] = turbojet.thrust

# Plot thrust evolution with altitude
plt.plot(altitude_array, thrust_array)
plt.xlabel("Altitude [m]")
plt.ylabel("Thrust [N]")
plt.title("Thrust evolution with altitude")
plt.show()