Test for the CL limitation during climb and cruise

docs/documentation/mission_module/mission_file/segments.rst

@@ -215,6 +215,9 @@ Mach 0.8 while keeping equivalent_airspeed constant).
       mach: constant                            #  level that provides maximum lift/drag
       altitude:                                 #  at current mass.
         value: optimal_flight_level
+    maximum_CL: 0.6                             # Limitation on lift coefficient.
+                                                # The altitude will be limited to the closest
+                                                # flight level within the CL limitation.
 
 .. seealso::
 
@@ -274,9 +277,11 @@ prepending climb, if any).
 An :code:`optimal_cruise` segment simulates a cruise climb, i.e. a cruise where the aircraft
 climbs gradually to keep being at altitude of maximum lift/drag ratio.
 
-It assumed the segment actually starts at altitude of maximum lift/drag ratio, which can be
+The :code:`optimal_cruise` segment can be realised at a constant lift coefficient using the parameter :code:`maximum_CL`.
+
+It assumed the segment actually starts at altitude of maximum lift/drag ratio or the altitude given by :code:`maximum_CL`, which can be
 achieved with an :ref:`segment-altitude_change` segment with :code:`optimal_altitude` as target
-altitude.
+altitude and :code:`maximum_CL` as parameter.
 
 *The common way to optimize the fuel consumption for commercial aircraft is a step climb cruise.
 Such segment will be implemented in the future.*
@@ -288,6 +293,7 @@ Such segment will be implemented in the future.*
     segment: optimal_cruise
     polar: data:aerodynamics:aircraft:cruise    # High speed aerodynamic polar
     engine_setting: cruise
+    maximum_CL: 0.6
     target:
       ground_distance:                          # Cruise for 2000 nautical miles
         value: 2000

src/fastoad/models/performances/mission/openmdao/tests/data/test_mission.xml

@@ -71,6 +71,14 @@
                     <fuel units="kg">
                         95.0<!--mass of consumed fuel during takeoff phase in sizing mission--></fuel>
                 </takeoff>
+                <main_route>
+                    <climb>
+                        <max_CL>0.65</max_CL>
+                    </climb>
+                    <cruise>
+                        <max_CL>0.65</max_CL>
+                    </cruise>
+                </main_route>
                 <taxi_out>
                     <thrust_rate>0.3</thrust_rate>
                     <duration units="s">143.</duration>
@@ -89,6 +97,14 @@
                     <fuel units="kg">
                         95.0<!--mass of consumed fuel during takeoff phase in sizing mission--></fuel>
                 </takeoff>
+                <main_route>
+                    <climb>
+                        <max_CL>0.65</max_CL>
+                    </climb>
+                    <cruise>
+                        <max_CL>0.65</max_CL>
+                    </cruise>
+                </main_route>
                 <taxi_out>
                     <thrust_rate>0.3</thrust_rate>
                     <duration units="s">143.</duration>

src/fastoad/models/performances/mission/openmdao/tests/data/test_mission.yml

@@ -83,6 +83,34 @@ phases:
           mach: constant
           altitude:
             value: optimal_flight_level
+        maximum_CL: ~max_CL
+  climb_optimal:
+    engine_setting: climb
+    polar: data:aerodynamics:aircraft:cruise
+    thrust_rate: 0.9
+    time_step: 5.0
+    parts:
+      - segment: altitude_change
+        target:
+          altitude:
+            value: 10000.
+            unit: ft
+          equivalent_airspeed: constant
+      - segment: speed_change
+        target:
+          equivalent_airspeed:
+            value: 300.
+            unit: kn
+      - segment: altitude_change
+        target:
+          equivalent_airspeed: constant
+          mach: 0.78
+      - segment: altitude_change
+        target:
+          mach: constant
+          altitude:
+            value: optimal_altitude
+        maximum_CL: ~max_CL
   descent:
     engine_setting: idle
     polar: data:aerodynamics:aircraft:cruise
@@ -155,6 +183,28 @@ routes:
       segment: cruise
       engine_setting: cruise
       polar: data:aerodynamics:aircraft:cruise
+      maximum_CL: ~max_CL
+    descent_parts:
+      - phase: descent
+  main_route_optimal:
+    distance_accuracy:
+      value: ~
+      default: 0.5
+      unit: km
+    range:
+      value: 2000.
+      unit: NM
+    climb_parts:
+      - phase: initial_climb
+      - phase: climb_optimal
+    cruise_part:
+      segment: optimal_cruise
+      engine_setting: cruise
+      polar: data:aerodynamics:aircraft:cruise
+      target:
+        altitude:
+          value: optimal_altitude
+      maximum_CL: ~max_CL
     descent_parts:
       - phase: descent
   diversion:
@@ -198,3 +248,9 @@ missions:
           ref: main_route
           multiplier: 0.03
     use_all_block_fuel: True
+  operational_optimal:
+    parts:
+      - route: main_route_optimal
+      - reserve:
+          ref: main_route_optimal
+          multiplier: 0.03

src/fastoad/models/performances/mission/openmdao/tests/data/test_mission_run.xml

@@ -94,6 +94,14 @@
                     <fuel units="kg">
                         95.0<!--mass of consumed fuel during takeoff phase in sizing mission--></fuel>
                 </takeoff>
+                <main_route>
+                    <climb>
+                        <max_CL>0.65</max_CL>
+                    </climb>
+                    <cruise>
+                        <max_CL>0.65</max_CL>
+                    </cruise>
+                </main_route>
                 <taxi_out>
                     <thrust_rate>0.3</thrust_rate>
                     <duration units="s">143.</duration>

src/fastoad/models/performances/mission/openmdao/tests/test_mission.py

@@ -20,7 +20,7 @@
 from scipy.constants import foot, knot, nautical_mile
 
 from fastoad._utils.testing import run_system
-from fastoad.io import DataFile
+from fastoad.io import DataFile, VariableIO
 from ..mission import OMMission
 from ..mission_run import AdvancedMissionComp
 from ..mission_wrapper import MissionWrapper
@@ -395,3 +395,83 @@ def test_mission_group_with_fuel_objective(cleanup, with_dummy_plugin_2):
 
     assert_allclose(problem["data:mission:fuel_as_objective:needed_block_fuel"], 10000.0, atol=1.0)
     assert_allclose(problem["data:mission:fuel_as_objective:reserve:fuel"], 260.0, atol=1.0)
+
+
+def test_mission_group_with_CL_limitation(cleanup, with_dummy_plugin_2):
+
+    input_file_path = pth.join(DATA_FOLDER_PATH, "test_mission.xml")
+    vars = VariableIO(input_file_path).read(
+        ignore=[
+            "data:mission:operational:main_route:climb:max_CL",
+            "data:mission:operational:main_route:cruise:max_CL",
+        ]
+    )
+    ivc = vars.to_ivc()
+
+    # Activate CL limitation during cruise and climb
+    ivc.add_output("data:mission:operational:main_route:climb:max_CL", val=0.45)
+    ivc.add_output("data:mission:operational:main_route:cruise:max_CL", val=0.45)
+
+    problem = run_system(
+        AdvancedMissionComp(
+            propulsion_id="test.wrapper.propulsion.dummy_engine",
+            out_file=pth.join(RESULTS_FOLDER_PATH, "CL_limitation.csv"),
+            use_initializer_iteration=False,
+            mission_file_path=MissionWrapper(
+                pth.join(DATA_FOLDER_PATH, "test_mission.yml"), mission_name="operational"
+            ),
+            reference_area_variable="data:geometry:aircraft:reference_area",
+        ),
+        ivc,
+    )
+
+    flight_points = problem.model.component.flight_points
+    climb_points = flight_points.loc[flight_points["name"] == "operational:main_route:climb"]
+    CL_end_climb = climb_points.CL.iloc[-1]
+    altitude_end_climb = climb_points.altitude.iloc[-1]
+
+    # check CL and flight level, CL is lower than 0.45 because the climb phase stops at the closest flight level.
+    assert_allclose(CL_end_climb, 0.445, atol=1e-3)
+    assert_allclose(altitude_end_climb, 9753.6, atol=1e-1)
+
+    # Now check climbing cruise with contant CL
+    ivc.add_output(
+        "data:mission:operational_optimal:main_route_optimal:climb_optimal:max_CL", val=0.45
+    )
+    ivc.add_output("data:mission:operational_optimal:main_route_optimal:cruise:max_CL", val=0.45)
+    ivc.add_output("data:mission:operational_optimal:taxi_out:thrust_rate", val=0.3)
+    ivc.add_output("data:mission:operational_optimal:taxi_out:duration", val=300, units="s")
+    ivc.add_output("data:mission:operational_optimal:takeoff:fuel", val=100, units="kg")
+    ivc.add_output("data:mission:operational_optimal:takeoff:V2", val=70, units="m/s")
+    ivc.add_output("data:mission:operational_optimal:TOW", val=70000, units="kg")
+
+    problem = run_system(
+        AdvancedMissionComp(
+            propulsion_id="test.wrapper.propulsion.dummy_engine",
+            out_file=pth.join(RESULTS_FOLDER_PATH, "CL_limitation.csv"),
+            use_initializer_iteration=False,
+            mission_file_path=MissionWrapper(
+                pth.join(DATA_FOLDER_PATH, "test_mission.yml"), mission_name="operational_optimal"
+            ),
+            reference_area_variable="data:geometry:aircraft:reference_area",
+        ),
+        ivc,
+    )
+
+    flight_points = problem.model.component.flight_points
+    climb_points = flight_points.loc[
+        flight_points["name"] == "operational_optimal:main_route_optimal:climb_optimal"
+    ]
+    cruise_points = flight_points.loc[
+        flight_points["name"] == "operational_optimal:main_route_optimal:cruise"
+    ]
+    CL_end_climb = climb_points.CL.iloc[-1]
+    altitude_end_climb = climb_points.altitude.iloc[-1]
+    altitude_end_cruise = cruise_points.altitude.iloc[-1]
+    CL_end_cruise = cruise_points.CL.iloc[-1]
+
+    # Check CL and altitude for a climbing cruise at constant CL.
+    assert_allclose(CL_end_climb, 0.45, atol=1e-3)
+    assert_allclose(CL_end_cruise, 0.45, atol=1e-3)
+    assert_allclose(altitude_end_climb, 9821.85, atol=1e-1)
+    assert_allclose(altitude_end_cruise, 10343.68, atol=1e-1)

src/fastoad/models/performances/mission/segments/time_step_base.py

@@ -69,8 +69,8 @@ class AbstractTimeStepFlightSegment(
     #: the flight path).
     time_step: float = DEFAULT_TIME_STEP
 
-    # The lift coefficient at which the cruise phase will be realised
-    CL_cruise: float = None
+    # The maximum lift coefficient for optimal climb and cruise segments
+    maximum_CL: float = None
 
     #: Minimum and maximum authorized altitude values. If computed altitude gets beyond these
     #: limits, computation will be interrupted and a warning message will be issued in logger.
@@ -318,8 +318,8 @@ def _get_optimal_altitude(
         def distance_to_optimum(altitude):
             atm = self._get_atmosphere_point(altitude)
             true_airspeed = mach * atm.speed_of_sound
-            if self.CL_cruise is not None:
-                CL_optimal = min(self.polar.optimal_cl, self.CL_cruise)
+            if self.maximum_CL is not None:
+                CL_optimal = min(self.polar.optimal_cl, self.maximum_CL)
             else:
                 CL_optimal = self.polar.optimal_cl
             optimal_air_density = (