Experimental Mechanism Study On The Flow Around Supersonic Optical Dome With Film Cooling And Its Aero-Optical Effects

During the precision guided missile's supersonic or hypersonic flying in the air, the complex structures of shock waves, expansive waves and turbulent boundary layer, etc, occur due to the interaction between the flow field of high speed and the optical dome. They result in the aero-optical effects such as bore-sight error, jitter, blur and intensity attenuation, then the precision of the missile will be decreased. Otherwise, by the action of the air with high speed, the temperature of the optical window will increase badly thus its properties will be impacted. So the optical window must be cooled. Blowing into supersonic gaseous film with low temperature above the optical window surface to cover it, is one of the effective cooling methods, but the flow field will become more complex and the aero-optical effects even worse.In this thesis, the experimental investigation of the flow field around the supersonic optical dome with cooling jet and its aero-optical effects has been performed. The Mach numbers of the free flow and the injected flow are 3.8 and 2.5 respectively. Three modes of experiments were carried out, namely mode of no jet, mode of the injection lip pressure matching with the exterior, and mode of the injection lip pressure higher.The spatial-temporal fine structures of the supersonic optical dome flow field under the three modes were caught via NPLS technique with high spatial-temporal resolution. The bow shock wave, expansion wave, recirculation region, reattachment region, laminar boundary layer and turbulent boundary layer are clearly visible while no injection. And under the condition of film cooling, the mixing layer is visible clearly above the optical window, and the film comes into being to protect the window from high-temperature environment thereby the window can be cooled. While the lip pressure is higher than the mainstream after the bow shock, the shock structures are more complex correspondingly and the laminar length of the mixing layer is even shorter while the turbulent region is larger nevertheless. The temporal evolution characteristics of the flow field are discussed via the analyzing of the two time-resolved NPLS images 5 microseconds apart under the three conditions respectively. Furthermore, the average temporal characteristic is discussed via lots of NPLS images.The nano-particles are used as tracers in the supersonic velocity measurement based on NPLS, and multi-kind of high precision PIV algorithms are introduced synthetically. Via this measurement, the velocity measuring of some section of the three-dimensional flow field can be obtained. The speed distributings of the flow field under the three modes were measured via this technique and the results reflected the flow field velocity nicely and revealed the dynamic characteristics of the flow field with or without injection.In order to analyze the distortion characteristics of the optical beam transmission through the flow field above the optical window further, the density measuring under the three conditions was carried out via the supersonic density measurement technique based on NPLS, and the instantaneous, time-averaged and instantaneous pulsation density fields were obtained respectively whose spatial resolutions are all micrometer magnitude. By the describing of the time-resolved density fields the density's temporal evolution can be discovered.Based on the results of the density fields with high spatial-temporal resolution, Ray-tracing theory was introduced to get the optical distortion of the flow field above the optical window transmitted by the planar wave front beam whose wavelength is 532 nanometers. The results show that the curve of the distortion without injection is simpler than that with injection relatively. Furthermore, the effects of the laminar and turbulent boundary layer and the mixing layer and the large scale structures in them on the optical distortion were discussed.