Unsteady characteristics of aerodynamic loads on a turret
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摘要: 采用耦合J-B模型的IDDES模型与双时间步LU-SGS方法开展炮塔非稳态气动载荷的数值仿真研究。炮塔流动会发生分离，天顶位置的分离角大于90°；当流动绕过炮塔时，形成马蹄涡、脱落涡街等非稳态流场结构，导致气动载荷也具有非稳态特性；炮塔顶点的脉动静压功率谱在1.6～40.0 kHz进入各向同性均匀湍流的惯性子区，基本满足Kolmogrov的−5/3定律；气动力以阻力为主，横向力的脉动幅值大，气动力矩则以俯仰力矩为主，滚转力矩的脉动幅值大，偏航力矩可以忽略不计；气动力和力矩的功率谱主要集中在1 kHz以下，存在多个尖峰频率，主频约为230 Hz（斯特劳哈尔数为0.15）。在ATP系统设计之初，需要考虑光学炮塔所受气动载荷的非稳态特性，并规避尖峰频率尤其是主频的谐振破坏问题。Abstract: IDDES coupled with J-B model and dual time step LU-SGS method has been adopted to carry out numerical simulation research on unsteady aerodynamic loads on a turret. Flow around the turret will separate, and the separation angle at the zenith is greater than 90°. When the flow bypasses the turret, unsteady flow field structures such as horseshoe vortex and shedding vortex street will form, resulting in unsteady aerodynamic loads. Power spectral density of pulsating static pressure at the zenith lies in the inertial sub-region of isotropic and uniform turbulence at 1.6-40.0 kHz, which basically satisfies Kolmogrov’s −5/3 law. Aerodynamic force is mainly drag force, fluctuation amplitude of transverse force is large, while aerodynamic moment is mainly pitching moment, fluctuation amplitude of rolling moment is also large, but yaw moment can be ignored. The power spectra of aerodynamic force and moment are mainly concentrated below 1 kHz, there are obvious peak frequencies, and the dominant frequency is about 230 Hz (Strouhal number is 0.15). At the beginning of the design of the acquisition tracking pointing (ATP) system, unsteady characteristics of aerodynamic loads on the turret should be considered, and resonant failure problem caused by peak frequencies, especially the dominant frequency, should be avoided.
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