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Stochastic Backscatter Model for Grey Area Mitigation in Hybrid RANS-LES Simulations by AngPass · Pull Request #2572 · su2code/SU2

and others added 2 commits

September 15, 2025 18:26
The Reynolds stress tensor definition is modified to include a random contribution, which is expressed as the curl of a normally-distributed stochastic vector potential.

pcarruscag

Add Langevin equations to Spalart-Allmaras solver (uncorrelated random source term) + add stochastic contribution to Reynolds stress tensor (using conservative variables from Langevin equations).

@AngPass

@pcarruscag pcarruscag changed the title Stochastic Backscatter Model for Grey Area Mitigation in Hybrid RANS-LES Simulations [WIP] Stochastic Backscatter Model for Grey Area Mitigation in Hybrid RANS-LES Simulations

Sep 23, 2025

github-advanced-security[bot]

Fix sanitizer warnings and regression test failures

- Address issues reported by clang sanitizers.
- Adjust implementation to ensure regression tests pass.
- Enhance readability.
- Ensure consistent declaration types.

@AngPass 

- Extend implementation to 2D configurations.
- Improve robustness.

@AngPass 

Enforce boundary conditions in Langevin equations.
- Implement a skew-symmetric scheme for the discretization of the convective terms in the Langevin equations.
- Fix the seed for the generation of the random source terms at the beginning of the simulation.

@AngPass 

- Add the flag for the simulation of the Decaying Isotropic Homogeneous Turbulence.
- Generate the initial velocity field matching the experimental data by Comte-Bellot & Corrsin.
- Include a preliminary test case.
- Implement flag to enforce LES in the whole domain.
- Add option to set the LES filter width to a user-specified value.
- Add velocity divergence to volume outputs.
- Remove internal generation of initial velocity field for simulating the Decaying Isotropic Homogeneous Turbulence (DIHT).

@AngPass 

- Add consistent evaluation of the turbulent kinetic energy in the random source term appearing in the momentum equations.
- Add backscatter intensity coefficient in the configuration file.
- Add random initialization of the Langevin variables.

@AngPass 

- Add Laplacian smoothing of source terms in Langevin equations.
Remark: pseudo-time integration is employed (residuals are printed on screen with fixed frequency, the maximum number of time iterations can be defined by the user).
- Fix redundancy in virtual member definition.
- Add stochastic source term to Spalart-Allmaras turbulence model equation (to ensure exchange of modeled and resolved kinetic energy).

@AngPass 

- Replace dual-time integration with Successive Over-Relaxation for Laplacian smoothing.
- Initialize stochastic vector potential as equal to the stochastic source terms in Langevin equations.
- Add random source term to main balance equations in LES zones exclusively.
- Blend RANS and LES turbulence timescales using the LES sensor.

@AngPass 

- Scale source terms in Langevin equations using Bessel functions to preserve the variance.
-  Compute Bessel integral at the beginning of the simulation for optimization.
- Add variance monitoring to screen output.

@AngPass

@AngPass

@AngPass

@AngPass 

- Add LD2 scheme to CONV_NUM_METHOD enum.
- Change scaling of the backscatter term.
- Increase the size of residual and Jacobian in turb_sources.hpp.
- Remove dynamic allocation in CTurbSASolver.cpp.
- Add helper function to compute relaxed backscatter intensity
  coefficient.
- Include pressure extrapolation in LD2 scheme formulation.
- Make code style homogeneous.

@AngPass 

- Redefine default values for backscatter parameters.
- Introduce RANS-LES blending factor for source terms in Langevin
  equations.
- Fix bug in MPI communication of slope limiters between periodic faces.

@AngPass 

- Add the option to apply the backscatter model only in a bounded box.
- Add the option to enforce backscatter where shielding function exceeds
  user-defined value.
- Correct bug in LD2 implementation.
- Make style consistent and update configuration template.

@AngPass

@AngPass

@AngPass 

- Modify the scaling of the stochastic forcing to include the modeled
  viscosity.
- Fix the computation of the stochastic tensor.
- Add the MPI communication of the DES lengthscale.

@AngPass AngPass marked this pull request as ready for review

March 2, 2026 11:03 
Remove outdated configuration file.
- Add the stochastic variables (from Langevin equations) to the restart
  file.
- Optimize the definition of the points lying inside the box where the
  backscatter model is active.
- Limit the turbulence time scale in RANS regions (Langevin equations).
- Add test case: spatially-developing mixing layer.

@AngPass

@AngPass

@pcarruscag pcarruscag changed the title [WIP] Stochastic Backscatter Model for Grey Area Mitigation in Hybrid RANS-LES Simulations Stochastic Backscatter Model for Grey Area Mitigation in Hybrid RANS-LES Simulations

Mar 16, 2026

pcarruscag