Transitional flow modelling for flow past a circular cylinder

Abstract

This thesis focuses on implementing and analyzing the original transitional Amplification Factor Transport (AFT) model, its extended version with Reynolds Stress Model (RSM) closure using Unsteady Reynolds Averaged Navier Stokes (URANS), and Delayed Detached-Eddy Simulation (DDES) approaches in OpenFOAMv1912. The aim is to enable transition prediction for correlation with wind tunnel tests at scaled-model Reynolds numbers. Verification confirms the required conditions for transition prediction, while validation demonstrates agreement between the implemented and original models. Predictions for transitional flow over a backward-facing step are first investigated. Results highlight the sensitivity in the laminar and transitional regions. AFT and AFT-RSM models demonstrate varying recirculation lengths, whereas Spalart-Allmaras (S-A) and k-ϵ models show constant recirculation lengths in both regimes. Additionally, AFT and AFT-RSM successfully predict the presence of a tertiary bubble, which is not captured by turbulence models. The performance of AFT-based models for flow past a circular cylinder is then explored. The findings reveal improved predictions compared to fully turbulent approaches across the upper-subcritical, critical, and supercritical regimes. In the upper subcritical regime, the AFT model enhances predictions of pressure, skin friction coefficient, and recirculation length. In the critical regime, although the models struggle with separation-transition interaction, they successfully capture the stretched wake and resulting drag reduction. AFT models demonstrate constant values of C_D and St in the supercritical regime, distinguishing them from γ - Re_θ and γ models. Additionally, the AFT-DDES model exhibits similar performance to AFT and AFT-RSM, while providing an improved description of wake behavior. The correlation study reveals differences between original AFT boundary layer properties and LES simulations for circular cylinder flow. The growth of H₁₂ vs H_L in the original model is steeper than LES results, while k_v vs H₁₂ shows faster growth in LES due to smaller momentum thicknesses. A single correlation is achieved by averaging both behaviours using two Reynolds numbers. Implemented in OpenFOAM, the new correlations delay transition by approximately two degrees compared to the modified original AFT model.

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Identifiers

ORCID for Jose Miguel Garro Fernandez: orcid.org/0000-0002-8298-0115

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