Computational drag analysis in the under-body for a sedan type car model

Contemporary vehicles are required to yield superior performance with low emissions, high stability, and a high fuel economy. For the same power output, the speed of the vehicle can be increased by reducing the drag force, which is resistance to the forward motion. Under-body region of the vehicle is often neglected because of its complex geometry and the presence of uneven and cleft structures which triggers separation and turbulence. As a result the flow is decelerated and the pressure gradient becomes unfavourable which increases the pressure drag. Designing the under-body more carefully, avoiding projections and covering open areas with panels reduce the turbulence and straighten the flow, thus yielding lower drag. In the present work, numerical analysis is first made on Ahmed body flow for three different slant angles and the flow process involved in drag production is observed. Simulation results in acceptable agreement with the experimental results and thus validates this work. Later the flow around a car and the under-body region is studied using Computational Fluid Dynamic (CFD) simulation techniques. Simulations are done on a sedan type car model. The geometry was rebuilt using the blueprints and physical measurements of the road version using DASSAULT System's CATIA V5R20. The geometry was exported to ANSYS for meshing in STP format and was meshed in the ANSYS workbench module. FLUENT is used for the analysis of the meshed geometry. The simulations revealed how force, pressure distribution and velocity fields varied for different configurations with and without wheels and also by the installation of diffusers. It is observed that 30% of the drag is contributed by wheels and wheel housing. By attaching diffusers it is found that the drag values are decreasing considerably along with getting more down force.