[WIP] Implementing variable density for unsteady incompressible flow #2641

tkiymaz · 2025-12-10T13:45:17Z

Proposed Changes

Implements variable density treatment for unsteady incompressible flow simulations. Currently, SU2 uses constant density in transient simulations, which is inaccurate for combustion cases where density varies significantly due to heat release and species composition changes. This contribution enables proper density updates during time-stepping for flamelet-based combustion modeling. For now, only 1st order time marching is implemented

Related Work

Related to incompressible flow solver and flamelet combustion modeling. No specific issue linked yet.

PR Checklist

I am submitting my contribution to the develop branch.
My contribution generates no new compiler warnings (try with --warnlevel=3 when using meson).
My contribution is commented and consistent with SU2 style (https://su2code.github.io/docs_v7/Style-Guide/).
I used the pre-commit hook to prevent dirty commits and used pre-commit run --all to format old commits.
I have added a test case that demonstrates my contribution, if necessary.
I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp), if necessary.

pcarruscag · 2025-12-10T16:14:23Z

@Cristopher-Morales can you review this pr please?

Removed commented-out code for setting density at local point.

Updated the comment for density retrieval to reflect changes for transient density handling.

Removed unnecessary blank lines in CIncEulerVariable.hpp

Removed unnecessary blank lines in CVariable.hpp

Removed unnecessary blank lines to improve code readability.

Cristopher-Morales · 2025-12-10T17:24:32Z

@Cristopher-Morales can you review this pr please?

Hi @pcarruscag !

Yes, I can help reviewing this PR.

Please let me know if you need something else from my side

Removed commented-out code and updated density calculation.

bigfooted · 2025-12-10T17:31:59Z

@Cristopher-Morales I guess the changes to the preconditioner can be removed from this PR since we now have your implementation

Removed unnecessary blank lines in SetPrimVar function.

Removed unnecessary blank lines in CVariable.cpp.

SU2_CFD/include/variables/CVariable.hpp

Removed debug print statement from SetPrimVar function.

SU2_CFD/include/output/COutput.hpp

Cristopher-Morales · 2025-12-10T17:58:13Z

SU2_CFD/include/variables/CIncEulerVariable.hpp

+
+  inline void Set_Density_time_n(unsigned long iPoint, su2double val) {
+    Density_time_n[iPoint] = val;
+  }


Documentation must be added, similar to the function above SetDensity, Same for the two functions below Set_Density_unsteady and GetDensity_time_n

SU2_CFD/src/solvers/CIncEulerSolver.cpp

Co-authored-by: Cristopher Morales <[email protected]>

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

SU2_CFD/src/variables/CIncNSVariable.cpp

Co-authored-by: Cristopher Morales <[email protected]>

Develop

SU2_CFD/src/variables/CIncNSVariable.cpp

SU2_CFD/src/solvers/CSpeciesFlameletSolver.cpp

  SU2_OMP_SAFE_GLOBAL_ACCESS(config->SetGlobalParam(config->GetKind_Solver(), RunTime_EqSystem);)

  SU2_OMP_FOR_STAT(omp_chunk_size)
+  //for (auto i_point = 0u; i_point < nPointDomain; i_point++) {


To fix this, remove the commented‑out for statement entirely. This eliminates dead commented‑out code while preserving the current behavior, which uses nPoint as the loop bound.

Concretely, in SU2_CFD/src/solvers/CSpeciesFlameletSolver.cpp, locate the SU2_OMP_FOR_STAT(omp_chunk_size) macro in CSpeciesFlameletSolver::Preprocessing and delete the line containing //for (auto i_point = 0u; i_point < nPointDomain; i_point++) {. No new methods, imports, or definitions are needed, and no other lines need to change.

SU2_CFD/src/solvers/CSpeciesFlameletSolver.cpp

bigfooted · 2026-01-16T17:59:24Z

SU2_CFD/include/output/COutput.hpp


  /*! \brief Minimum required volume fields for restart file. */
-  const std::vector<string> restartVolumeFields = {"COORDINATES", "SOLUTION", "SENSITIVITY", "GRID_VELOCITY"};
+  const std::vector<string> restartVolumeFields = {"COORDINATES", "SOLUTION", "SENSITIVITY", "GRID_VELOCITY", "DENSITY_TIME_N", "DENSITY_TIME_N1"};


add density only with unsteady

bigfooted · 2026-01-16T18:02:13Z

SU2_CFD/src/solvers/CIncEulerSolver.cpp

+Density_time_n = nodes->GetDensity_time_n(iPoint);
+V2U(Density_time_n, V_time_n, U_time_n);


bigfooted · 2026-01-16T18:02:24Z

SU2_CFD/src/solvers/CIncEulerSolver.cpp

+V2U(Density_time_nM1, V_time_nM1, U_time_nM1);
+V2U(Density_time_n, V_time_n, U_time_n);
+V2U(Density, V_time_nP1, U_time_nP1);


SU2_CFD/src/solvers/CSpeciesFlameletSolver.cpp

SU2_CFD/src/variables/CIncNSVariable.cpp

Tahsin Berk Kiymaz and others added 3 commits June 17, 2025 10:28

my changes

509a608

my changes

6aeb0a3

specieschanges

79e238c

tkiymaz added the PR: draft label Dec 10, 2025

Remove slurm files from repository

526b9a1

bigfooted added bug changelog:fix labels Dec 10, 2025

pcarruscag assigned Cristopher-Morales Dec 10, 2025

tkiymaz added 7 commits December 10, 2025 18:08

Remove unnecessary blank line in COutput.hpp

59979d0

Clean up commented-out density setting code

99abfa4

Removed commented-out code for setting density at local point.

Update density retrieval comment for transient handling

bee5a27

Updated the comment for density retrieval to reflect changes for transient density handling.

Remove empty line before temperature setter comment

cea69cc

Clean up whitespace in CIncEulerVariable.hpp

a721a2e

Removed unnecessary blank lines in CIncEulerVariable.hpp

Clean up blank lines in CVariable.hpp

02c03bb

Removed unnecessary blank lines in CVariable.hpp

Clean up CFlowIncOutput.cpp by removing blank lines

0449bb4

Removed unnecessary blank lines to improve code readability.

Clean up CompleteImplicitIteration and update dRhodT

572291f

Removed commented-out code and updated density calculation.

tkiymaz added 7 commits December 10, 2025 18:32

Revert back the preconditioning to original

c9fd0f6

Remove unnecessary whitespace and debug print statement

fc33c6a

Clean up blank lines in CIncNSVariable.cpp

644a543

Removed unnecessary blank lines in SetPrimVar function.

Clean up whitespace in CVariable.cpp

fed4892

Removed unnecessary blank lines in CVariable.cpp.

Fix constructor signature for CSpeciesVariable

8e09f7f

Remove unnecessary blank line in CSpeciesVariable.cpp

1e5008a

Fix constructor signature for CSpeciesFlameletVariable

2aebc54

Cristopher-Morales reviewed Dec 10, 2025

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Remove debug output from SetPrimVar method

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Removed debug print statement from SetPrimVar function.

Cristopher-Morales reviewed Dec 10, 2025

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Merge branch 'develop' into fix_inc_unsteady_density

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tkiymaz and others added 5 commits December 18, 2025 12:56

Update SU2_CFD/src/solvers/CIncEulerSolver.cpp

630856b

Co-authored-by: Cristopher Morales <[email protected]>

Update SU2_CFD/src/solvers/CIncEulerSolver.cpp

35ad976

Co-authored-by: Cristopher Morales <[email protected]>

Update SU2_CFD/src/solvers/CIncEulerSolver.cpp

31f8af3

Co-authored-by: Cristopher Morales <[email protected]>

Potential fix for code scanning alert no. 5888: Unused local variable

00ae736

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Merge branch 'develop' into fix_inc_unsteady_density

8a47539

Cristopher-Morales reviewed Dec 18, 2025

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Cristopher-Morales and others added 9 commits December 18, 2025 21:38

Merge branch 'develop' into fix_inc_unsteady_density

4f7a656

Update SU2_CFD/src/variables/CIncNSVariable.cpp

df27a84

Co-authored-by: Cristopher Morales <[email protected]>

Merge branch 'develop' into fix_inc_unsteady_density

51f18af

Merge pull request #2698 from su2code/develop

8f6da27

Develop

Merge branch 'develop' into fix_inc_unsteady_density

524fd46

Merge branch 'develop' into fix_flame_init

acfe778

fix mpi and flame init

adedf6b

Merge branch 'fix_flame_init' into fix_inc_unsteady_density

89661d4

guards

df28101

github-advanced-security bot found potential problems Jan 16, 2026

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SU2_CFD/src/variables/CIncNSVariable.cpp Fixed Show fixed Hide fixed

revert

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bigfooted reviewed Jan 16, 2026

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Apply suggestion from @bigfooted

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02c3311

@@ -88,11 +88,11 @@
               SU2_OMP_SAFE_GLOBAL_ACCESS(config->SetGlobalParam(config->GetKind_Solver(), RunTime_EqSystem);)
               SU2_OMP_FOR_STAT(omp_chunk_size)
-              //for (auto i_point = 0u; i_point < nPointDomain; i_point++) {
               for (auto i_point = 0u; i_point < nPoint; i_point++) {
                 CFluidModel* fluid_model_local = solver_container[FLOW_SOL]->GetFluidModel();
                 su2double* scalars = nodes->GetSolution(i_point);
                 for (auto iVar = 0u; iVar < nVar; iVar++) scalars_vector[iVar] = scalars[iVar];
+                for (auto iVar = 0u; iVar < nVar; iVar++) scalars_vector[iVar] = scalars[iVar];
                 /*--- Compute total source terms from the production and consumption. ---*/
                 unsigned long misses = SetScalarSources(config, fluid_model_local, i_point, scalars_vector);

		Density_time_n = nodes->GetDensity_time_n(iPoint);
		V2U(Density_time_n, V_time_n, U_time_n);

[WIP] Implementing variable density for unsteady incompressible flow #2641

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[WIP] Implementing variable density for unsteady incompressible flow #2641

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tkiymaz commented Dec 10, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Proposed Changes

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pcarruscag commented Dec 10, 2025

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Cristopher-Morales commented Dec 10, 2025

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tkiymaz commented Dec 10, 2025 •

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