Water-flow Simulation on Vehicle Panels by Taking into Account the Calculated Aerodynamic Field 2005-01-3572
A numerical methodology using 3D computational fluid dynamics (CFD) was developed to simulate the water flows on vehicles in order to check the specifications under rain (visibility of door mirror by the driver, sealing…), or to evaluate washing efficiency (washing headlight, washing windshield …). The CFD method is constituted by a three step procedure.
In the first step, the aerodynamic field around the vehicle is calculated with Powerflow software in a large domain. It uses a Lattice Boltzmann approach to solve airflow. The existing process of Powerflow computation developed by aerodynamic and aeroacoustic teams of Renault SAS was adapted to refine results in high gradients of velocity zones.
In the second step, the field of air velocity vectors calculated with Powerflow is mapped towards a small domain where the water flow will be solved.
In the last step, the calculation carried out by N3S CFD code with a fluid film model gives the water distribution on different parts of the vehicle by taking into account the aerodynamic results. Several evolutions of the N3S code were performed by Renault to modelize the thin liquid film. It includes wall film formation by impinging rain and wall film separation by free surface instabilities. It considers also film transport such as governed by mass, momentum and energy equations with wall and air flow interactions.
Results were compared with the tests carried out on the Modus car in a wind tunnel reproducing the main characteristics of moving traffic under the rain. The water flow on the panel is well reproduced by the computations for four different A-pillar shapes.
This methodology is now applied by Renault to optimize design of next vehicles several months before the first physical prototype. In future works, we will use this tool to predict the rain evacuation of other parts of the vehicle, as for example the water-box under the hood.