There is a violent interaction between the optical hood of an object flying at supersonic speed in the atmosphere and the atmosphere. The gas density around the hood changes. Due to the gas refractive index pulsation of the flow field or the high temperature, the detection window is deformed, which makes the optical imaging system The aberration of the target image increases sharply, such as distortion, blur, offset, jitter, etc., which affect the transmission of light. This effect is called pneumatic shock wave optical effect. The shock wave effect is the first aero-optical effect formed after the object interacts with the atmosphere. The shock wave will cause the optical system to defocus, the optical transfer function will be distorted, and the image quality will decrease.
During the supersonic flow of water vapor, nucleation and condensation will occur, accompanied by the formation of condensation waves. When the high-speed water vapor in the non-equilibrium state meets the shock wave, the steam parameters on the wave front change drastically. The dissipation effect of the shock wave makes the two-phase flow velocity decrease instantaneously, the steam temperature rises suddenly, and a large number of tiny droplets are fast. evaporation. When the shock wave acts on the nucleation condensation zone, the nucleation condensation weakens or even disappears, and the two-phase flow will become a single-phase flow.
In fluid mechanics, it is extremely important to characterize the strong intermittent movement of the physical quantity that reflects the main characteristics of the flow field, especially the shock wave (also called shock wave). The place where the main parameters of the airflow change significantly is called a shock wave. The shock wave of an ideal gas has no thickness. It is a discontinuous surface in the mathematical sense. The actual gas has viscosity and heat transfer. This physical property makes the shock wave continuous, but the process is still very rapid. Therefore, the actual shock wave has a thickness, but the value is very small, only a certain multiple of the free path of gas molecules. The larger the relative supersonic Mach number of the wavefront, the smaller the thickness value. There is friction between gas and gas inside the shock wave, which converts part of the mechanical energy into heat energy. Therefore, the appearance of shock waves means the loss of mechanical energy and the generation of wave resistance, that is, energy dissipation effects. Since the thickness of the shock wave is very small, the internal conditions of the shock wave are generally not studied. What is related is the parameter change before and after the gas flows through the shock wave. Think of it as an adiabatic compression process.
Pneumatic shock wave are classified into normal shock waves, oblique shock waves, isolated shock waves, conical shock waves, etc. in terms of their shape.
