MIRA阶背式模型的瞬态流动结构分析

应用采用格子玻尔兹曼方法的PowerFLOW软件,结合非常大涡模拟方法,对MIRA阶背模型进行非稳态流场求解,研究外流场的结构及流动特性.通过分析时均流场中气流从A柱沿着车顶至C柱、车尾的流动过程,探索了C柱涡、D柱涡、部分分离涡的结构及流动机理.通过分析瞬态流场探索了更加精确的随机流动特性,其中时域流场分析部分,发现车轮、后风窗及车尾区域处流场结构复杂;对频域结果的分析进一步展示了涡的振动频率及其脉动特点,发现车尾上方振动频率达12 Hz,侧窗、发动机舱顶部,车顶及车身侧部的振动频率为23 Hz,并探究了振动频率的形成机理,压力脉动分析发现底盘上方、车身尾部及后轮区域存在较大振动能量,推断得出以上区域流场结构复杂,对阻力贡献大.将仿真结果与实验结果对比分析,二者流场结构相似,涡核的数量和位置都具有较好的一致性,验证了仿真的可靠性.

Instantaneous Flow Structure Analysis of MIRA Notchback Model

Applying the PowerFLOW software using the Lattice Boltzmann Method (LBM), and combining with the very Large Eddy Simulation Method (VLES), the unsteady flow field of the MIRA notchback model was solved to study the structure and flow characteristics of the external flow field. By analyzing the process of the flow from the A-pillar along the roof to the C-pillar and the rear of the flow field, the structure and flow mechanism of the C-pillar vortex, D-pillar vortex, and partial separation vortex were explored. The transient flow field was analyzed to explore more precise random flow characteristics. In the time domain flow field analysis part, the flow field structure of the wheel, rear wind window and rear part is complicated. The analysis results of the frequency domain further showed the vibration frequency and pulsation characteristics of the vortex. The vibration frequency of the rear part is 12Hz, and the vibration frequency of the side window, top of the engine compartment, roof, and side of the body is 23Hz. In addition, the formation mechanism of the vibration frequency was explored. By analyzing the pressure pulsation, it is found that large vibration energy occurs around the chassis, rear part of the vehicle body, and rear wheel area. It is concluded that the flow field structure in the above area is complex and it contributes a lot to the drag. When comparing the simulation results with the experimental results, the flow field structure is similar, and the number and position of the vortex cores are well consistent, which verifies the reliability of the simulation.