Fluid structure interaction analysis on the aerodynamic performance of underbody panels

Abstract

Underbody panels cover the rough surface under the car in order to reduce turbulence. They have a weak structure and might deform when subjected to the surrounding high speed ow. It is important to consider this deformation and to analyse how it might a ect the performance of the underbody panels, both aerodynamic (drag and lift forces) and structural (stresses). In this thesis, analyses on these underbody panels are perfomed using a method called Fluid Structure Interaction (FSI). In FSI the uid and structure are treated as a coupled system. A FSI script-based system for steady analysis has been created between the uid solver Ansys Fluent and the structural solver MSC Nastran. Results from simulations have been validated with the already available FSI software System Coupling in Ansys Workbench. The results showed that the deformations of the underbody panels were small. These small deformations had no major impact on the drag, lift or stresses in the panels. The maximum deformations of the underbody panels were in the range between 0.2-0.3 mm, with a maximum stress of about 3.0 MPa. Evaluation of the FSI method used in this project, showed that a deforming mesh is the most important and challenging area. The method for mesh movement in this project was not robust enough. Therefore another method for moving the mesh have to be implemented in the future. The small deformations of the underbody panels, from steady state simulations, indicate that it is faster and easier to only consider the pressure from the high speed ow. For future analyses of underbody panels and other systems with small deformations, it could be relevant to consider time-dependent simulations. Oscillations in systems, noise and failure due to vibrations are important to evaluate.