典型底部结构对轿车侧风稳定性的影响及作用机理

凹凸底部和光滑底部是进行轿车车身设计与布置时2种典型的设计方案，但底部结构对轿车侧风稳定性的作用机理尚不明确，厘清其影响不仅可为底部结构设计与布置提供参考数据，而且是进行轿车侧风稳定性评价的关键技术问题。通过建立典型底部结构轿车的数值计算模型，分析了不同侧风风速对轿车气动力和气动力矩的影响规律；采用汽车空气动力学与汽车系统动力学耦合方法建立了典型底部结构轿车的侧风稳定性分析与评价模型，研究了底部结构对轿车侧偏运动、横摆运动以及侧滑运动的影响规律及作用机理。研究表明：凹凸底部结构会增加轿车的气动升力、气动俯仰力矩、气动阻力以及气动侧力，加剧轿车的侧偏运动和横摆运动，增加轿车侧滑的风险；路面附着系数越低，凹凸底部结构对轿车侧偏运动和横摆运动的影响越大、对侧滑临界风速的影响越小。

Influence of typical under-body structureon car crosswind stability and the mechanism

There are two typical design solutions in the car body design and layout: concave-convex under-body and smooth under-body. However, the effects of the under-body structure on the crosswind stability of the car is not clear, and clarifying the effects not only provides reference data for the design and layout of the bottom structure, but also is a key technical problem for the crosswind stability evaluation of car. Firstly, the numerical calculation model of typical bottom structure cars was established, and the influence laws of different side wind speeds on the aerodynamic force and aerodynamic moment of the cars were analyzed. Secondly, based on the coupling method of automobile aerodynamics and automobile system dynamics, the crosswind stability analysis and evaluation model of typical bottom structure cars was established, and the influence laws and mechanism of the under-body structure on the lateral motion, yawing motion and side-slip motion of the car were studied. The study shows that the concave-convex bottom structure causes an increase in aerodynamic lift force, pitch moment, drag, and side force, which not only intensifies the lateral motion and yaw motion of the cars under crosswind, but also increases the risk of cars skidding. The lower the tire-road friction coefficient, the greater the effect of the concave and convex bottom structure on the lateral motion and yaw motion, and the smaller the effect on the limit wind speed of lateral slipping.