CAJ | 학술논문

超声速光学头罩在大气层内飞行时,需要在光学窗口表面顺来流方向进行喷流冷却,致使窗口上方流场更为复杂.目标光线穿过窗口上方流场,受到激波、膨胀波、混合层、湍流边界层等流场结构引起的变密度场影响而产生波前畸变,导致成像出现偏移、抖动、模糊等气动光学效应.本文对马赫数3.8来流条件下有无喷流时超声速光学头罩流场引起的气动光学波前畸变进行了试验研究.基于纳米示踪的平面激光散射技术,首先对流场图像进行密度校准获得高时空分辨率密度场,然后采用光线追迹法计算得到波长532 nm平面光波垂直于光学窗口穿过流场后的光程差(optical path difference, OPD)分布,并对窗口上方近壁区有无喷流状态的流场结构引起的OPD分布进行了研究.发现无喷流时,流场结构相对较为简单,窗口上方有较长的回流区和层流区,而有喷流时窗口上方出现复杂的剪切层、混合层及湍流边界层,流动很快就转捩为湍流结构,其引起的气动光学畸变要明显高于无喷流状态.无喷流状态相隔5μs的流场引起的光程差均方根值分别为0.0348和0.0356μm,有喷流状态的光程差均方根值分别为0.0462和0.0485μm.
초성속광학두조재대기층내비행시,수요재광학창구표면순래류방향진행분류냉각,치사창구상방류장경위복잡.목표광선천과창구상방류장,수도격파、팽창파、혼합층、단류변계층등류장결구인기적변밀도장영향이산생파전기변,도치성상출현편이、두동、모호등기동광학효응.본문대마혁수3.8래류조건하유무분류시초성속광학두조류장인기적기동광학파전기변진행료시험연구.기우납미시종적평면격광산사기술,수선대류장도상진행밀도교준획득고시공분변솔밀도장,연후채용광선추적법계산득도파장532 nm평면광파수직우광학창구천과류장후적광정차(optical path difference, OPD)분포,병대창구상방근벽구유무분류상태적류장결구인기적OPD분포진행료연구.발현무분류시,류장결구상대교위간단,창구상방유교장적회류구화층류구,이유분류시창구상방출현복잡적전절층、혼합층급단류변계층,류동흔쾌취전렬위단류결구,기인기적기동광학기변요명현고우무분류상태.무분류상태상격5μs적류장인기적광정차균방근치분별위0.0348화0.0356μm,유분류상태적광정차균방근치분별위0.0462화0.0485μm.
@@@@During the flight in the atmosphere, the optical window of an optical dome needs to be cooled, and supersonic film cooling is one of the economic ways. After traversing through the complex flow field above the window, the optical wave would be distorted by fluctuations in the density field due to the expansion wave, shockwave, mixing layer, turbulent boundary layer, etc. The aero-optical aberrations induced by the flow field of an optical dome in the presence and in the absence of the gas injection at Mach 3.8 are investigated experimentally. Based on the nano-tracer planar laser scattering (NPLS) technique, the density field with high spatial-temporal resolution is first obtained by the flow image calibration, and then the optical path difference (OPD)fluctuations of the original 532 nm planar wavefront perpendicular to the window are calculated using Ray-tracing theory. Also the OPD fluctuations caused by the near-wall region flow structures are presented. In the absence of the gas injection, the flow structure is relatively simple with a long recirculation and laminar region, while in the presence of the gas injection, there appear more complex structures such as shear layer, mixing layer and turbulent boundary layer and the flow is converted into turbulence quickly. Clearly, the optical aberration in the presence of the gas injection is degraded more. For example, the values of root-mean-square OPD (OPDrms) in the absence of the gas injection are 0.038 μm and 0.0356 μm, and they are 0.0462 μm, and 0.0485 μm in the presence of the gas injection during the interval 5 μs.