{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/153786"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/153786","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES","abstract":"While high-fidelity, scale-resolving methods in Computational Fluid Dynamics (CFD) are increasingly applied, the cost of these methods remains a significant barrier to their effective use. In this thesis, a new wall model is developed based upon a modified version of the Spalart-Allmaras (SA) turbulence model that lessens the near-wall grid requirements. This is achieved by, below the log layer, making the eddy viscosity approach a constant, non-zero value, and the velocity, which has a non-zero slip, varying approximately linearly with distance from the wall while maintaining the same total shear stress. The wall model introduces one parameter which controls the near-wall behavior of the solution. Unlike typical wall models, this method avoids the need to query the interior solution by utilizing a boundary condition which only requires solution information present at the boundary, making it well-suited for unstructured grids and mesh adaptation. The new approach is combined with mesh adaptation and applied to ReynoldsAveraged Navier-Stokes (RANS), demonstrating accurate predictions of quantities of interest such as aerodynamic coefficients, surface pressure and temperature, skin friction, and heat transfer compared with standard RANS-SA, while requiring substantially less near-wall grid to resolve the solution. Additionally, the new wall model and modified turbulence model are applied to Detached Eddy Simulation (DES) in a hybrid RANS/LES framework, where it is demonstrated that the wall model allows for reliable solutions on near-wall grids that are significantly coarser in the wall-normal direction than those used typically for DES. Finally, the wall model boundary condition is applied to wall-stress Wall-Modeled Large Eddy Simulation (WMLES) and shown to produce similar results to the traditional equilibrium model, while avoiding the need to query the interior solution.","abstract_html":"While high-fidelity, scale-resolving methods in Computational Fluid Dynamics (CFD) are increasingly applied, the cost of these methods remains a significant barrier to their effective use. In this thesis, a new wall model is developed based upon a modified version of the Spalart-Allmaras (SA) turbulence model that lessens the near-wall grid requirements. This is achieved by, below the log layer, making the eddy viscosity approach a constant, non-zero value, and the velocity, which has a non-zero slip, varying approximately linearly with distance from the wall while maintaining the same total shear stress. The wall model introduces one parameter which controls the near-wall behavior of the solution. Unlike typical wall models, this method avoids the need to query the interior solution by utilizing a boundary condition which only requires solution information present at the boundary, making it well-suited for unstructured grids and mesh adaptation. The new approach is combined with mesh adaptation and applied to ReynoldsAveraged Navier-Stokes (RANS), demonstrating accurate predictions of quantities of interest such as aerodynamic coefficients, surface pressure and temperature, skin friction, and heat transfer compared with standard RANS-SA, while requiring substantially less near-wall grid to resolve the solution. Additionally, the new wall model and modified turbulence model are applied to Detached Eddy Simulation (DES) in a hybrid RANS/LES framework, where it is demonstrated that the wall model allows for reliable solutions on near-wall grids that are significantly coarser in the wall-normal direction than those used typically for DES. Finally, the wall model boundary condition is applied to wall-stress Wall-Modeled Large Eddy Simulation (WMLES) and shown to produce similar results to the traditional equilibrium model, while avoiding the need to query the interior solution.","abstract_has_math":false,"creators":["Ursachi, Carmen-Ioana"],"institution":"Massachusetts Institute of Technology","degree_name":"Doctoral","degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Aeronautics and Astronautics","school":null,"contributors":[],"advisors":["Darmofal, David L."],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-02","date_published":"2024-02","updated_at":"2026-07-22T22:22:23Z","subjects":[],"languages":[],"rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"rights_urls":["https://rightsstatements.org/page/InC-EDU/1.0/"],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/1721.1/153786","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Darmofal, David L."]},{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. 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In this thesis, a new wall model is developed based upon a modified version of the Spalart-Allmaras (SA) turbulence model that lessens the near-wall grid requirements. This is achieved by, below the log layer, making the eddy viscosity approach a constant, non-zero value, and the velocity, which has a non-zero slip, varying approximately linearly with distance from the wall while maintaining the same total shear stress. The wall model introduces one parameter which controls the near-wall behavior of the solution. Unlike typical wall models, this method avoids the need to query the interior solution by utilizing a boundary condition which only requires solution information present at the boundary, making it well-suited for unstructured grids and mesh adaptation. The new approach is combined with mesh adaptation and applied to ReynoldsAveraged Navier-Stokes (RANS), demonstrating accurate predictions of quantities of interest such as aerodynamic coefficients, surface pressure and temperature, skin friction, and heat transfer compared with standard RANS-SA, while requiring substantially less near-wall grid to resolve the solution. Additionally, the new wall model and modified turbulence model are applied to Detached Eddy Simulation (DES) in a hybrid RANS/LES framework, where it is demonstrated that the wall model allows for reliable solutions on near-wall grids that are significantly coarser in the wall-normal direction than those used typically for DES. Finally, the wall model boundary condition is applied to wall-stress Wall-Modeled Large Eddy Simulation (WMLES) and shown to produce similar results to the traditional equilibrium model, while avoiding the need to query the interior solution."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph.D."]},{"key":"dc:title","label":"Title","values":["A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES"]}]}],"canonical_facts":{"dc:contributor.advisor":["Darmofal, David L."],"dc:contributor.department":["Massachusetts Institute of Technology. Department of Aeronautics and Astronautics"],"dc:creator":["Ursachi, Carmen-Ioana"],"dc:date.accessioned":["2024-03-15T19:23:59Z"],"dc:date.available":["2024-03-15T19:23:59Z"],"dc:date.issued":["2024-02"],"dc:description.abstract":["While high-fidelity, scale-resolving methods in Computational Fluid Dynamics (CFD) are increasingly applied, the cost of these methods remains a significant barrier to their effective use. In this thesis, a new wall model is developed based upon a modified version of the Spalart-Allmaras (SA) turbulence model that lessens the near-wall grid requirements. This is achieved by, below the log layer, making the eddy viscosity approach a constant, non-zero value, and the velocity, which has a non-zero slip, varying approximately linearly with distance from the wall while maintaining the same total shear stress. The wall model introduces one parameter which controls the near-wall behavior of the solution. Unlike typical wall models, this method avoids the need to query the interior solution by utilizing a boundary condition which only requires solution information present at the boundary, making it well-suited for unstructured grids and mesh adaptation. The new approach is combined with mesh adaptation and applied to ReynoldsAveraged Navier-Stokes (RANS), demonstrating accurate predictions of quantities of interest such as aerodynamic coefficients, surface pressure and temperature, skin friction, and heat transfer compared with standard RANS-SA, while requiring substantially less near-wall grid to resolve the solution. Additionally, the new wall model and modified turbulence model are applied to Detached Eddy Simulation (DES) in a hybrid RANS/LES framework, where it is demonstrated that the wall model allows for reliable solutions on near-wall grids that are significantly coarser in the wall-normal direction than those used typically for DES. Finally, the wall model boundary condition is applied to wall-stress Wall-Modeled Large Eddy Simulation (WMLES) and shown to produce similar results to the traditional equilibrium model, while avoiding the need to query the interior solution."],"dc:description.degree":["Ph.D."],"dc:identifier.uri":["https://hdl.handle.net/1721.1/153786"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["In Copyright - Educational Use Permitted","Copyright retained by author(s)"],"dc:rights.uri":["https://rightsstatements.org/page/InC-EDU/1.0/"],"dc:title":["A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES"],"dc:type":["Thesis"],"thesis:degree_name":["Doctoral","Doctor of Philosophy"]},"updated_at":"2026-07-22T22:22:23Z"}