su2code · pcarruscag · Mar 17, 2026 · Mar 9, 2026 · Mar 11, 2026 · Mar 11, 2026
diff --git a/Common/include/CConfig.hpp b/Common/include/CConfig.hpp
@@ -932,6 +932,7 @@ class CConfig {
   Pressure_Thermodynamic,          /*!< \brief Thermodynamic pressure of the fluid. */
   Temperature_FreeStream,          /*!< \brief Total temperature of the fluid.  */
   Temperature_ve_FreeStream;       /*!< \brief Total vibrational-electronic temperature of the fluid.  */
+  bool out2in_mdot_engine;         /*!< \brief Flag to use engine outlet mass flow as engine inlet mass flow. */
   unsigned short wallModel_MaxIter; /*!< \brief maximum number of iterations for the Newton method for the wall model */
   su2double wallModel_Kappa,        /*!< \brief von Karman constant kappa for turbulence wall modeling */
   wallModel_B,                      /*!< \brief constant B for turbulence wall modeling */
@@ -2118,6 +2119,12 @@ class CConfig {
    */
   su2double GetNuFactor_Engine(void) const { return NuFactor_Engine; }
 
+  /*!
+   * \brief Get the flag to use exhaust mass flow as inlet mass flow.
+   * \return TRUE if exhaust mass flow is used as inlet mass flow.
+   */
+  bool GetExhaustToInlet_Engine(void) const { return out2in_mdot_engine; }
+
   /*!
    * \brief Get the value of the non-dimensionalized actuator disk turbulence intensity.
    * \return Non-dimensionalized actuator disk intensity.

diff --git a/Common/src/CConfig.cpp b/Common/src/CConfig.cpp
@@ -1793,6 +1793,8 @@ void CConfig::SetConfig_Options() {
   addEnumOption("ENGINE_INFLOW_TYPE", Kind_Engine_Inflow, Engine_Inflow_Map, FAN_FACE_MACH);
   /* DESCRIPTION: Evaluate a problem with engines */
   addBoolOption("ENGINE", Engine, false);
+  /* DESCRIPTION: Use exhaust mass flow as inlet mass flow. */
+  addBoolOption("ENGINE_EXHAUST_TO_INLET", out2in_mdot_engine, false);
 
   /* DESCRIPTION:  Sharpness coefficient for the buffet sensor */
   addDoubleOption("BUFFET_K", Buffet_k, 10.0);

diff --git a/SU2_CFD/src/solvers/CEulerSolver.cpp b/SU2_CFD/src/solvers/CEulerSolver.cpp
@@ -7622,6 +7622,17 @@ void CEulerSolver::BC_Engine_Inflow(CGeometry *geometry, CSolver **solver_contai
 
     Target_Inflow_MassFlow = config->GetEngineInflow_Target(Marker_Tag) / (config->GetDensity_Ref() * config->GetVelocity_Ref());
 
+    if (config->GetExhaustToInlet_Engine()) {
+      su2double Outlet_MF = 0.0;
+      unsigned short nMarker_Global = config->GetnMarker_CfgFile();
+      for (unsigned short iMarker_Global = 0; iMarker_Global < nMarker_Global; iMarker_Global++) {
+        if (config->GetMarker_CfgFile_KindBC(config->GetMarker_CfgFile_TagBound(iMarker_Global)) == ENGINE_EXHAUST) {
+          Outlet_MF = Outlet_MF + config->GetExhaust_MassFlow(config->GetMarker_CfgFile_TagBound(iMarker_Global));
+        }
+      }
+      Target_Inflow_MassFlow = Outlet_MF;
+    }
+
     if (config->GetSystemMeasurements() == US) Target_Inflow_MassFlow /= 32.174;
 
     if (Engine_HalfModel) Target_Inflow_MassFlow /= 2.0;

diff --git a/TestCases/euler/turbofan_MFR_coupling/MFR_coupling.cfg b/TestCases/euler/turbofan_MFR_coupling/MFR_coupling.cfg
@@ -0,0 +1,106 @@
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%                                                                              %
+% SU2 configuration file                                                       %
+% Case description: Turbofan with outlets-to-inlet mass-flow rate coupling___  %
+% Author: Angelo Passariello and Mauro Minervino_____________________________  %
+% Institution: Italian Aerospace Research Centre (CIRA)______________________  %
+% Date: 16/03/2026                                                             %
+% File Version 8.4.0 "Harrier"                                                 %
+%                                                                              %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
+%
+SOLVER= EULER
+MATH_PROBLEM= DIRECT
+RESTART_SOL= NO
+%
+% ------------------------------- SOLVER CONTROL ------------------------------%
+%
+ITER= 10000
+CONV_FIELD= RMS_DENSITY
+CONV_RESIDUAL_MINVAL= -15
+CONV_STARTITER= 10
+%
+% -------------------- COMPRESSIBLE FREE-STREAM DEFINITION --------------------%
+%
+MACH_NUMBER= 0.16719966920674
+AOA= 0.0
+INIT_OPTION= TD_CONDITIONS
+FREESTREAM_OPTION= DENSITY_FS
+FREESTREAM_PRESSURE= 101325.0
+FREESTREAM_TEMPERATURE= 288.15
+REYNOLDS_NUMBER= 3.8951057985067e+6
+FREESTREAM_DENSITY= 1.225
+FREESTREAM_VELOCITY= ( 56.897550640000, 0.0, 0.0 )
+FREESTREAM_VISCOSITY= 1.78938027807758E-05
+REF_DIMENSIONALIZATION= DIMENSIONAL
+%
+% ---------------------- REFERENCE VALUE DEFINITION ---------------------------%
+%
+% Reference origin for moment computation (m or in)
+REF_ORIGIN_MOMENT_X = 0.00
+REF_ORIGIN_MOMENT_Y = 0.00
+REF_ORIGIN_MOMENT_Z = 0.00
+REF_LENGTH= 1.0
+REF_AREA= 1.0
+SEMI_SPAN= 1.0
+%
+% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
+%
+MARKER_EULER= ( INTAKE, NOZZLE_TE, PLUG_TE, PLUG, NACELLE_TE, SPINNER, LIP, NOZZLE_INNER, NOZZLE, NACELLE_INNER, COWL )
+MARKER_FAR= ( FF )
+ENGINE_INFLOW_TYPE= FAN_FACE_MDOT
+ENGINE_EXHAUST_TO_INLET= YES
+DAMP_ENGINE_INFLOW= 0.01
+MARKER_ENGINE_INFLOW= ( FAN_IN, 140.0 )
+MARKER_ENGINE_EXHAUST= ( FAN_OUT, 289.761088684333, 103321.726628227, CORE_OUT, 289.761088684333, 103321.726628227 )
+%
+% ------------------------ SURFACES IDENTIFICATION ----------------------------%
+%
+MARKER_PLOTTING = ( NOZZLE_TE, PLUG_TE, PLUG, NACELLE_TE, SPINNER, LIP, INTAKE, NOZZLE_INNER, NOZZLE, NACELLE_INNER, COWL, FAN_IN, FAN_OUT, CORE_OUT )
+MARKER_MONITORING = ( NACELLE_TE, LIP, COWL )
+MARKER_ANALYZE = ( FAN_IN, FAN_OUT, CORE_OUT )
+MARKER_ANALYZE_AVERAGE = MASSFLUX
+%
+% ------------- COMMON PARAMETERS DEFINING THE NUMERICAL METHOD ---------------%
+%
+NUM_METHOD_GRAD= GREEN_GAUSS
+NUM_METHOD_GRAD_RECON = GREEN_GAUSS
+CFL_NUMBER= 1.0
+%
+% ----------- SLOPE LIMITER AND DISSIPATION SENSOR DEFINITION -----------------%
+%
+MUSCL_FLOW= NO
+MUSCL_TURB= YES
+%
+% ------------------------ LINEAR SOLVER DEFINITION ---------------------------%
+%
+LINEAR_SOLVER= FGMRES
+LINEAR_SOLVER_ITER= 5
+%
+% -------------------- FLOW NUMERICAL METHOD DEFINITION -----------------------%
+%
+CONV_NUM_METHOD_FLOW= JST
+LOW_MACH_PREC= YES
+ENTROPY_FIX_COEFF= 0.001
+%
+% ------------------------- SCREEN/HISTORY VOLUME OUTPUT --------------------------%
+%
+SCREEN_OUTPUT= (INNER_ITER, RMS_DENSITY, LIFT, DRAG, SURFACE_MASSFLOW)
+HISTORY_OUTPUT= (ITER, AERO_COEFF, RMS_RES, AOA, NONPHYSICAL_POINTS, SURFACE_MASSFLOW, SURFACE_STATIC_PRESSURE)
+VOLUME_OUTPUT= (COORDINATES, SOLUTION, PRIMITIVE)
+OUTPUT_WRT_FREQ= 1000
+WRT_FORCES_BREAKDOWN= YES
+%
+% ------------------------- INPUT/OUTPUT FILE INFORMATION --------------------------%
+%
+SURFACE_FILENAME= surface_flow
+VOLUME_FILENAME= flow
+RESTART_FILENAME= restart_flow.dat
+MESH_FILENAME= engine-alone.cgns
+MESH_FORMAT= CGNS
+TABULAR_FORMAT= TECPLOT
+OUTPUT_FILES= (RESTART, TECPLOT, SURFACE_TECPLOT)
+READ_BINARY_RESTART= YES
+REORIENT_ELEMENTS= YES
diff --git a/TestCases/parallel_regression.py b/TestCases/parallel_regression.py
@@ -301,6 +301,14 @@ def main():
     ramp_msw.test_vals = [-7.522451, -1.791193, -0.077520, 0.054427]
     test_list.append(ramp_msw)
 
+    # MFR_coupling
+    MFR_coupling           = TestCase('MFR_coupling')
+    MFR_coupling.cfg_dir   = "euler/turbofan_MFR_coupling"
+    MFR_coupling.cfg_file  = "MFR_coupling.cfg"
+    MFR_coupling.test_iter = 100
+    MFR_coupling.test_vals = [-2.1124e+02, 1.5003e+02, 2.0151e+01]
+    test_list.append(MFR_coupling)
+
     ##########################
     ###  Compressible N-S  ###
     ##########################

diff --git a/config_template.cfg b/config_template.cfg
@@ -1183,6 +1183,9 @@ MARKER_ENGINE_INFLOW= ( NONE )
 % Format: (engine exhaust marker, total nozzle temp, total nozzle pressure, ... )
 MARKER_ENGINE_EXHAUST= ( NONE )
 %
+% Flag to allow mass-flow rate coupling between all exhaust surfaces and the engine inlet (YES, NO)
+ENGINE_EXHAUST_TO_INLET= NO
+%
 % Displacement boundary marker(s) (NONE = no marker)
 % Format: ( displacement marker, displacement value normal to the surface, ... )
 MARKER_NORMAL_DISPL= ( NONE )