小入射角条件下气动光学成像偏移

Aero-Optical Imaging Deviation under the Small-Incidence-Angle Condition

针对超声速飞行器在大气中飞行时由于气动光学效应产生的成像偏移,推导了光线偏折角和流场折射率梯度之间的关系,给出了小入射角情况下,离散折射率场光线偏折角的一种计算方法;利用不同流场的计算流体力学数据计算出对应的折射率场;使用光线追迹法得到光线通过不同流场后的偏折角和传播路径上的折射率梯度分布。仿真结果表明,新的偏折角计算方法所得结果在入射角小于30°时与Runge-Kutta和Snell光线追迹法具有很好的一致性;同一高度下小入射角时,光线的偏折角并不随着飞行速度的增加而增加,而是基本保持稳定;光线通过流场的偏折是正负折射率梯度区域共同作用的结果,负的折射率梯度区域可以减少光线偏折,起到部分"校正"作用。

The non-uniform flow field around the vehicle flying at a high speed bends the incident ray and imposes an imaging deviation on the imaging plane. The relation between the deflection angle and the refractive index gradient is derived theoretically, and a new method is proposed to compute the deflection angle when the ray is passing through the discrete refractive index field with a small incidence angle. Then fluid-dynamics computations under different flying conditions have been completed. After that the mean density field is converted into the refractive index field. Ray tracing is performed to obtain the deflection angle and the gradients along the propagation path. The results show that the computed results by our method are well consistent with those by the Runge-Kutta and the Snell method when the incidence angle is less than 30°; and at the same altitude, the imaging deviation does not grow as the flying speed increases under the small incidence-angle condition, but remains stable; the deflection angle is determined by the positive as well as the negative refractive index gradient region, and the negative refractive index gradient region may reduce the imaging deviation.