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为了明确汽车车身俯仰运动对气动升力的影响,建立了某轿车车身俯仰运动模型,并采用大涡模拟对其进行了准静态及瞬态模拟分析。利用动网格技术实现了车身绕前轴中心的正弦俯仰运动,并通过稳态的1∶3模型风洞试验验证了大涡模拟法的准确性。从车身周围流场、车身表面压力等不同的角度对气动升力变化规律及机理进行了分析。结果表明:车身正弦俯仰运动时,瞬态气动升力也随之发生周期性变化,与准静态下气动升力的变化完全不一致,准静态模拟与试验条件下气动升力变化趋势基本一致;瞬态模拟时最大和最小气动升力系数都约为准静态模拟时的3倍;瞬态模拟时,由于流场中气流受到惯性以及黏性作用的影响,导致最大和最小气动升力系数都出现在车身接近水平位置时,与准静态模拟及试验中出现位置完全不同;车身俯仰运动时,车身上表面的压力变化相对较小,而车底板的压力变化很大,且对气动升力有着重要影响,车身从不同方向运动到水平位置时,底板后端的气动压力相差近40N;后轮胎周围的流场变化对气动升力也有重要影响,车身从不同方向运动到水平位置时,后轮罩中心截面上相同位置处和后轮胎后端表面的压力系数最大差值均约为0.4。
In order to clarify the influence of vehicle body pitching on aerodynamic lift, a vehicle pitching motion model of a car is established, and its quasi-static and transient simulation analysis is carried out by using large eddy simulation. The kinematic grid technique was used to realize the sinusoidal pitch motion around the center of the front axle. The accuracy of the large eddy simulation method was verified by a steady state 1: 3 model wind tunnel test. The change law and mechanism of aerodynamic lift are analyzed from different angles such as the flow field around the body, the body surface pressure and so on. The results show that the transient aerodynamic lift changes periodically along with the sinusoidal pitching motion, which is completely different from the change of the aerodynamic lift in the quasi-static state. The trend of the aerodynamic lift under quasi-static simulation and experimental conditions is basically the same. The maximum and minimum aerodynamic lift coefficients are about three times that of the quasi-static simulation. In the transient simulation, the maximum and minimum aerodynamic lift coefficients appear at the level of the vehicle body due to the inertia and viscous effect of the airflow in the flow field When compared with the quasi-static simulation and test position completely different; body pitch movement, the body surface pressure changes are relatively small, while the car floor pressure varies widely, and the aerodynamic lift has an important impact on the body from different directions When moving to the horizontal position, the aerodynamic pressure at the back end of the bottom plate is nearly 40N; the flow field around the rear tire also has an important influence on aerodynamic lift. When the vehicle body moves from different directions to a horizontal position, The maximum difference of the pressure coefficient of the rear tire surface is about 0.4.