Validation of Lattice-Boltzmann Aerodynamics Simulation for Vehicle Lift Prediction

Abstract

Simulation tools are used in the design of vehicles to reduce the cost of development and to find robust engineering solutions earlier in the design process. Prediction of drag using aerodynamics simulation is critical for assessing aerodynamic efficiency of designs, including upper body shape, underbody surfaces, wheels and aerodynamic treatments such as spoilers, deflectors and underbody covers. The Lattice-Boltzmann Simulation approach has been used broadly to simulate both steady and unsteady flow regimes accurately and to provide robust prediction of drag. Beyond drag, other vehicle performance metrics are now predicted using this type of simulation such as, for example, wind noise levels, heat exchanger performance, brake cooling and thermal protection of sensitive components. In particular, aerodynamic lift is important for production vehicles for assessing handling attributes at high speed. In this paper, the validation of aerodynamics simulation for vehicle lift is examined and extended through a study of three detailed full-scale vehicles. For high-performance road vehicles the front- and rear-axle lift force, and the balance between them, are critical for driving dynamics for highway driving and must be considered along with the drag during development. Often a trade-off between lift and drag performance is required for a successful design. Furthermore, since the lift is highly dependent on the detailed pressure distribution in the underbody region and near the wheels, evaluation of lift should also account for on-road effects using rotating wheels and moving ground plane. In this study the drag, front lift and rear lift were evaluated using Lattice-Boltzmann Simulation and compared to full-scale wind-tunnel tests, using both static- and moving-ground configurations. Care was taken to include the effect of the floor boundary layer, suction system, moving belt and rotating tires, all of which are designed to emulate on-road conditions inside a wind-tunnel. The results show good prediction of both drag and lift performance, and provide confidence to extend the use of aerodynamic simulation for lift prediction earlier in the design process.