气动光学平均流场效应时间特性研究

Simulation on Time-Dependent Aero-Optic Effects of Mean Flow Field

根据气动光学效应定义了绕流流场厚度,分析了气动光学平均流场效应的时间特性与绕流流场厚度的关系,给出特征时间的粗估公式。使用大型流体计算软件SAED模拟计算了机载光学平台绕流流场随时间的变化,计算了绕流流场厚度,研究了气动光学平均场效应随时间的变化规律。计算结果验证了粗估公式的可靠性,表明与湍流效应的特征时间相似,气动光学平均流场效应的特征时间,正比于绕流流场厚度与飞机速度的比值。在给定的计算模型中,特征时间约为5ms量级,特征频率低于300Hz;平均流场气动光学效应引起的光程差均方根随时间围绕平均值变化,方差与平均值之比约为8%。

The thickness of flow field around the platform is defined based on aero-optical effect, the relationship between the thickness of flow field around the platform and the characteristic time of the aero-optic effect for the mean flow is investigated, and the rough estimation formula of characteristic time is given. Using large computational fluid dynamics software （SAED）, the change of airborne optical flow field around the platform with respect to time and the thickness of flow field is computed, and change rule of aero-optic effect for the mean flow is researched. The calculation results verify the reliability of the rough estimation formula. It is shown that characteristic time of the aero-optic effect for the mean flow field is proportional to the ratio between thickness of flow field and the plane speed, which is in agreement with that of turbulence effect. In the given model, characteristic time is about 5 ms, and the characteristic frequency is less than 300 Hz. The root mean square of optical-path difference induced by the aero-optic effect for the mean flow field varies around a mean value with time. The ratio of variance to mean value is about 8 %.