A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES
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) turbul...
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Format: | Thesis |
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Massachusetts Institute of Technology
2024
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Online Access: | https://hdl.handle.net/1721.1/153786 |
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author | Ursachi, Carmen-Ioana |
author2 | Darmofal, David L. |
author_facet | Darmofal, David L. Ursachi, Carmen-Ioana |
author_sort | Ursachi, Carmen-Ioana |
collection | MIT |
description | 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. |
first_indexed | 2024-09-23T16:37:10Z |
format | Thesis |
id | mit-1721.1/153786 |
institution | Massachusetts Institute of Technology |
last_indexed | 2024-09-23T16:37:10Z |
publishDate | 2024 |
publisher | Massachusetts Institute of Technology |
record_format | dspace |
spelling | mit-1721.1/1537862024-03-16T03:02:46Z A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES Ursachi, Carmen-Ioana Darmofal, David L. Massachusetts Institute of Technology. Department of Aeronautics and Astronautics 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. Ph.D. 2024-03-15T19:23:59Z 2024-03-15T19:23:59Z 2024-02 2024-02-16T20:56:46.026Z Thesis https://hdl.handle.net/1721.1/153786 In Copyright - Educational Use Permitted Copyright retained by author(s) https://rightsstatements.org/page/InC-EDU/1.0/ application/pdf Massachusetts Institute of Technology |
spellingShingle | Ursachi, Carmen-Ioana A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title | A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title_full | A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title_fullStr | A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title_full_unstemmed | A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title_short | A Stress-equivalent Spalart-Allmaras Wall Model with Local Boundary Conditions for RANS, DES, and LES |
title_sort | stress equivalent spalart allmaras wall model with local boundary conditions for rans des and les |
url | https://hdl.handle.net/1721.1/153786 |
work_keys_str_mv | AT ursachicarmenioana astressequivalentspalartallmaraswallmodelwithlocalboundaryconditionsforransdesandles AT ursachicarmenioana stressequivalentspalartallmaraswallmodelwithlocalboundaryconditionsforransdesandles |