Évaluation d’un modèle transitionnel dans le cas de la formation d’une bulle de décollement laminaire

Abstract

This work focuses on the numerical simulation of laminar separation bubbles in the field of ventilation and aeronautics, with an emphasis on applications operating at low to moderate Reynolds numbers ranging from 104 to 106. When a fluid flows along a wall, a thin layer of flow, known as the boundary layer, forms near the surface. This boundary layer is generally considered laminar for low Reynolds numbers. However, when the laminar boundary layer face to an adverse pressure gradient, a phenomenon called laminar separation occurs. Within this separation bubble, transition phenomena occur, and under certain conditions, they can lead to the formation of a turbulent boundary layer downstream of the bubble. The main objective of this research is to evaluate the performance of a numerical model for solving the Reynolds-averaged Navier-Stokes equations (a statistical approach to turbulence) adapted to transitional flows. The model studied in this work is called ▯ − ▯▯▯ and is based on a semi-empirical approach. This model, implemented in the ANSYS CFX5 software, is evaluated on a well-documented experimental configuration that reproduces a laminar separation bubble. The Thermofluids Laboratory for Transportation at ÉTS has a test rig suitable for this study. Thus, modelling the flow within this experimental setup will allow evaluating the capability of the ▯ − ▯▯▯ model to accurately reproduce phenomena related to laminar separation bubbles. The model validation, therefore, relies on its ability to faithfully reproduce the characteristics of the boundary layer under these specific conditions. The model succeeds in reproducing the development of a laminar boundary layer on a flat plate, as well as its response to an adverse pressure gradient. Moreover, the characteristics of the modelled separation bubble are in agreement with those reported in the literature. Finally, the model adequately represents the transition to a turbulent boundary layer downstream of the bubble. With its ability to reproduce these phenomena and its relatively short computational time, the ▯ − ▯▯▯ model constitutes a valuable tool for industrial applications at low to moderate Reynolds numbers.

Date	2 Aug 2023
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Marlène Sanjosé (Supervisor)