Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J40: Turbulence Modeling I |
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Chair: Oanh Pham, University of Oklahoma Room: 355 F |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J40.00001: Velocity gradient partitioning in turbulent flows Rahul Arun, Tim Colonius A normality-based triple decomposition of the velocity gradient tensor reveals contributions from three distinct modes of deformation: axial straining, rigid rotation, and pure shearing. We use this decomposition to partition the strength of velocity gradient fluctuations in several canonical turbulent flows, including forced isotropic turbulence, channels and boundary layers, and subsonic and transonic jets. For forced isotropic turbulence, the partitioning agrees well with previous results. For the wall-bounded flows, the partitioning collapses onto the isotropic partitioning far from the wall, where the mean shearing is relatively weak. By contrast, the near-wall partitioning is dominated by shearing. Between these two regimes, the partitioning collapses reasonably well as a function of the mean shearing strength. For the turbulent jets, the isotropic partitioning applies broadly due to the rapid decay of the shear layer near the nozzle lip. Before reaching the potential flow regime, the partitioning near the turbulent/non-turbulent interface is associated with an enhanced relative contribution from rigid rotation. Given our results, the velocity gradient partitioning shows promise for modeling a broad class of turbulent flows. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J40.00002: Analysis of Non-Equilibrium Turbulent Boundary Layers using RANS Taygun R Gungor, Dogukan T Karahan, Eren B Kaya, Ayse G Gungor Incorporating the effects of flow history and non-locality in non-equilibrium flows represents the current state-of-the-art in Reynolds-Averaged Navier-Stokes (RANS) modeling for practical applications. This study investigates the performance of RANS models for three non-equilibrium turbulent boundary layers of Gungor et al. (IJHFF (2016), 59:109-124; JFM (2022), 948:A5; arXiv:2402.13067). Two of the flows are subjected to an adverse pressure gradient (APG), one of which includes a separation bubble. The third flow transitions from an upstream APG section to a downstream favorable pressure gradient section. The flows are analyzed using RANS simulations with eddy-viscosity-based models and Reynolds stress models, and results are compared with the DNS data of Gungor et al. Preliminary RANS results exhibit qualitative agreement with DNS data. Ongoing work focuses on the detailed analysis of history effects and their impact on model performance. These investigations aim to enhance the understanding and accuracy of RANS models for non-equilibrium turbulent flows. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J40.00003: Identifying permitted triadic interactions and their effect on amplitude modulation in a turbulent channel flow Miya Y Coimbra, Beverley J McKeon We define criteria for quantifying permittable interactions between triadically compatible, spatio-temporal wavenumbers in a turbulent channel flow. Permitted interactions are determined based on the relative strength of the nonlinearly interacting modes and the strength of the interaction of the entire wavenumber triad, termed the interaction coefficient. The effect of these permitted interactions on the amplitude modulation statistic is studied in the framework of phase relationships; specifically, the relative phase between the large scales and the envelope of the small scales. A triad-by-triad approach is taken to explore the effects of individual triadic relationships on the amplitude modulation coefficient. We determine whether there are key interactions that persist across the channel height and look at how the number of permitted interactions change as a function of wall-normal distance. Ultimately, taking an individual triad approach to study the interactions between large- and small-scales lends itself well to low-order modeling applications as it may provide insight to key interactions that govern the flow and allow for a reduction in the number of scales required to describe the system. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J40.00004: Variational data assimilation of 3D wake flows using limited experimental observations. Uttam Cadambi Padmanaban, SAMARESH MIDYA, Bharathram Ganapathisubramani, Sean P Symon In this study, we use variational data assimilation to reconstruct the mean velocity field around a wake generator using limited experimental observations. Stereo PIV is employed to obtain mean velocity fields along the spanwise plane at ten equally spaced locations in the streamwise direction in the wake of the wake generator. The available data on discrete planes makes it challenging to compute quantities such as vorticity. Spalart-Allmaras (SA) RANS turbulence model is used to conduct a baseline simulation of the same test case but suffers from errors particularly in the regions of strong recirculation. We improve the prediction of the SA model and expand the field of view offered by the limited experimental observations using data assimilation. We use variational data assimilation with the discrete adjoint method to optimize a control parameter by minimizing the discrepancy between the experimental and RANS mean velocity fields. The topological differences between the CFD mesh and the experimental grid are resolved by using a cell-averaging method which is fully implemented in the discrete adjoint solver DAFoam. We test two control parameters – a scalar multiplier to the SA turbulence transport equation and a source term to the momentum equations. The performance of the two control parameters in using limited experimental data to accurately reconstruct the mean velocity field is assessed. We also quantify the influence of data sparsity on accuracy of reconstruction. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J40.00005: ABSTRACT WITHDRAWN
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