title: Scale-resolving modeling of heat and mass transfer in IC engine-relevant impinging flow configurations: Sensitized RANS-RSM-based turbulence anisotropy characterization
Creators: name: Bopp, Maximilian
Publisher: name: UNSPECIFIED
Year: 2024

description: The present work provides insights into momentum, heat and species transport phenomena occurring under highly anisotropic turbulent conditions, such as those encountered in conventional, wall-parallel channel flows, variously designed wall-perpendicular flow impingement configurations, and complex internal combustion (IC) engine intake flow configuration. The main focus of the present thesis is to investigate the predictive performance of a baseline second-moment closure Reynolds-Averaged Navier-Stokes Reynolds-Stress Model (RANS-RSM) and its scale-resolving extension, the Improved Instability- Sensitive Reynolds-Stress Model (IISRSM) (Jakirlić and Maduta, 2015), employed within a sensitized RANS concept in conjunction with first- and second-order modeling approaches for the turbulent heat and species flux. A comparative assessment of the predictive performance of the two RANS-RSM related models in terms of their ability to correctly predict coupled, simultaneously occurring momentum, heat and species transport processes is performed for a turbulent channel, slot-jet impingement, axisymmetric-jet impingement, double-slot-jet impingement and IC intake flow configuration. As an important step in model development all respective flow configurations are compared with corresponding reference Direct Numerical Simulations (DNS) and Large Eddy Simulations (LES). To evaluate the general physical realizibility of the momentum transport, the turbulence anisotropy is characterized by utilizing the invariant maps of Lumley and Newman (1977) and Choi and Lumley (2001) as well as the related barycentric map suggested by Banerjee, Krahl, Durst, and Zenger (2007). To further represent the second-order Reynolds stress anisotropy tensor field within the computational domain, a barycentric coloring approach (Emory and Iaccarino, 2014) is applied to all numerical datasets. The modeling of the turbulent heat and species flux within the corresponding temperature and species transport equation is realized by the isotropic simple gradient diffusion (SGDH) and anisotropic modeling approaches, such as the generalized gradient diffusion (GGDH) or the higher order quadratic gradient diffusion hypothesis (HOGGDH) originally proposed by Abe and Suga (2001). The baseline RSM in combination with the considered heat flux models provided a reasonable prediction for temperature and species transfer and the corresponding distribution of some relevant integral properties, such as the Nusselt number. The scale-resolving IISRSM provided significantly better predictions for velocity, Reynolds stress components, and temperature and concentration profiles, closely following the DNS and LES reference. To accurately predict the near wall behavior of thermal and species fields, a RANS-based model, whether in the conventional or sensitized RANS framework, must capture not only the underlying velocity field but also the anisotropic Reynolds stress tensor. Sensitizing a second-order Reynolds stress model to adequately resolve the fluctuating turbulence can significantly improve the prediction of the flow structure in terms of all dependent flow properties, such as velocity, Reynolds stress, species and thermal fields, considering that a significant fraction of the turbulent spectrum has been resolved.