The Study Of Optical Properties And Diagnostic Schemes On High-temperature Complex Flow Fields

With the rapid development of modern aviation, spaceflight, rocket and missile technologies, it urgently requires to visualize and measure the key parameters of complex flow fields from low to high temperature region. By comparison, optical computerized tomography (OCT) technology has its unique advantages in visualizing and measuring key parameters of high-temperature complex flow fields, with the real-time, stable, non-contact characteristics. However, it is a pity, so far, there is no suitable OCT diagnostic theory for high-temperature complex flow fields, which can be attributed to the optical properties of the high-temperature complex flow fields have not been well studied. In response to this actuality, this dissertation will focus on the optical properties and tomography diagnostic theory of such flow fields. Based on these, the complete theoretical models and experimental system, which are adapted to high-temperature complex flow fields'optical computerized tomography diagnosis, will be established and expected to provide valuable reference on better solving such kinds of flow fields'3-D visualization and the key parameters'measurement and diagnosis. In a word, the main tasks are as follows:In view of the effect of a variety of charged particles and compositions on the optical properties of high-temperature complex flow fields, the original G-D formula is amended, so as to provide necessary theoretical basis for these flow fields'OCT diagnosis. As a result, a uniform refractive index descriptive model is established for the common gas and high-temperature complex flow fields. Besides, by comparing the moire fringes displacement of the flame and argon arc plasma, the main factor which determines the refractive index gradient of high-temperature flow fields is clarified. According to which, the applicability of moire deflection tomography on high temperature flow fields'diagnosis is analyzed.The dependence of dispersive capability on probe wavelength and flow fields'species composition, temperature and pressure is deduced for three typical high-temperature complex flow fields---flame, rocket exhaust and argon arc plasma. Then, the dispersion characteristic of them is studied, which indicates that the dispersive capability of flame and rocket exhaust decreases with the temperature increasing, while that of the argon arc plasma is the non-monotonic function of temperature. If the pressure is latm, the maximal dispersive capability of the argon arc plasma always appears at 17000K. Besides, the choice of suitable optical diagnostic means for three typical high-temperature complex flow fields is discussed. Based on the complex dielectric constant. and regarding the arc plasma as an example. the absorption coefficient is given in the visible and infrared's three atmospheric windows regions. The dependence of the absorption coefficient on the wavelength shows that, the absorption coefficient's order of magnitude in the visible range is 1-2 smaller than that in the three atmospheric windows of the infrared. For a certain probe wavelength, the absorption coefficient is approximately a linear function of the pressure, but a nonlinear function of the temperature. Based on the non-linear relation, the physical essence what determines the flow field's maximal absorptive ability is indicated. The above results will supply theoretical reference for choosing the suitable probe wavelength to diagnose these flow fields, meanwhile, they will also provide certain valuable reference for analyzing the feasibility of applying optical communication technology in the reentry process.Moire deflection tomography is adopted to display and diagnose the flame and argon arc plasma, and the refractive index distributions of them are given. On the basis of systemically analyzing the species composition distribution characteristic of the flame, the temperature partition reconstruction theory and method is proposed by the phase distribution. By comparison, it is found that the temperature distribution is more reasonable and practical, when the distribution of species composition is considered. On the basis of further deducing the temperature reconstruction model and considering the distribution of pressure for the argon arc plasma, the temperature of it is obtained, which amends the isotonic process hypothesis. The condition, which can be used to determine whether the flow field meets the isotonic pressure hypothesis in the process of temperature reconstruction, is proposed. The involved studies will provide a good foundation for ultimately improving the key parameters' measurement accuracy in flow fields'optical computerized tomography diagnosis.This dissertation is expected to play a positive role in the visualization as well as the application and development of OCT in the measurement of the key parameters for the high-temperature complex flow fields.