An eddy viscosity PANS model for non-zonal continuous hybrid RANS/LES simulations

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dc.contributor.author Eid, Maher
dc.date.accessioned 2022-08-10T10:45:22Z
dc.date.available 2022-08-10T10:45:22Z
dc.date.copyright 2022 en_US
dc.date.issued 2022-05-10
dc.identifier.uri http://hdl.handle.net/10725/13919
dc.description.abstract The extremely stringent requirement of fully resolving turbulence in Direct Numerical Simulation (DNS) of fluid flows has forced researchers and engineers to rely heavily on averaged methods like the Reynolds’ Averaged Navier-Stokes (RANS) for common engineering applications. The process of averaging in RANS results in the full spectrum of turbulent scales being fully modeled instead of resolved as in DNS. This comes at a cost of lower accuracy and reliability, which could have adverse effects on the design or research at hand. With the current computer technology barely keeping up with Moore’s law, it is expected that we are decades away from having enough computing power to make DNS a feasible option outside purely academic settings. The huge gap between RANS and DNS has led to the development of hybrid models that offer the benefits of both extremes, by allowing part of turbulence to be exactly resolved, thus reducing the inaccuracies associated with the smaller modeling part. Partially Averaged Navier-Stokes (PANS) bridges between RANS and DNS, providing the adequate balance between modeled and resolved quantities. In this study, a new PANS model based on the one-equation transport of the unresolved turbulent eddy viscosity νtu is proposed. This is, to the author’s knowledge, the first PANS model in which the resolution level is controlled by the ratio of unresolved-to-total turbulent eddy viscosity fνt . In addition, fνt is both a spatially and temporally varying quantity derived directly from the integration of the energy density spectrum. This gives the proposed model a more physically sound formulation, compared to the empiricism and ad-hoc shielding usually used in hybrid models. Two validation test cases are investigated, with the first involving shear flow between a moving and stationary fluid i.e., the backward-facing step, and the external aerodynamic flow over a simplified car body, i.e., the Ahmed body. Both cases are simulated using the proposed model, Improved Delayed Detached Eddy Simulation (IDDES), and Wall Modeled Large Eddy Simulation (WMLES). The latter two models are also scale-resolving methods used for comparison in the current study. Validation of the results are performed against data from well established experimental setups. The proposed PANS model shows higher accuracy in predicting the average velocity profiles, as well as the turbulent stresses in the backward-facing step compared to IDDES and WMLES. In addition, PANS is able to release more structures than the other models for the same grid density, showing that strong shielding is not always an advantage. For external aerodynamics applications, i.e., the Ahmed Body, PANS shows better drag predictions with levels of turbulent stresses comparable to IDDES. With the given grid of this case, PANS is able to automatically adjust the level of resolution to cover upstream locations with a fully modeled formulation, and switch to a more resolving one on the slant and downstream the body. Overall, the proposed PANS model shows promising results in this preliminary study. en_US
dc.language.iso en en_US
dc.subject Turbulence -- Mathematical models en_US
dc.subject Eddies -- Mathematical models en_US
dc.subject Reynolds stress -- Mathematical models en_US
dc.subject Fluid dynamics en_US
dc.subject Lebanese American University -- Dissertations en_US
dc.subject Dissertations, Academic en_US
dc.title An eddy viscosity PANS model for non-zonal continuous hybrid RANS/LES simulations en_US
dc.type Thesis en_US
dc.term.submitted Spring en_US
dc.author.degree PHD en_US
dc.author.school SOE en_US
dc.author.idnumber 201405102 en_US
dc.author.commembers El Cheikh, Amne
dc.author.commembers El Khatib, Nader
dc.author.department Industrial And Mechanical Engineering en_US
dc.description.physdesc 1 online resource (xii, 66 leaves): ill. (some col.) en_US
dc.author.advisor ElKhoury, Michel
dc.keywords Turbulence modelling en_US
dc.keywords Partially Averaged Navier-Stokes en_US
dc.keywords Scale-Resolving methods en_US
dc.keywords Hybrid RANS/LES en_US
dc.keywords Backward-facing step en_US
dc.keywords Ahmed body en_US
dc.description.bibliographiccitations Includes bibliographical references (leaf 64-66) en_US
dc.identifier.doi https://doi.org/10.26756/th.2022.406
dc.author.email maher.eid@lau.edu.lb en_US
dc.identifier.tou http://libraries.lau.edu.lb/research/laur/terms-of-use/thesis.php en_US
dc.publisher.institution Lebanese American University en_US
dc.author.affiliation Lebanese American University en_US

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