INFLUENCE REGULARITIES OF EXTERNAL THERMAL ACTIONS ON THE SURFACE OF OPTICAL FAIRINGS IN IR-DEVICES UNDER THE CONDITIONS OF THEIR APPLICATION

Abstract

Till present, the heating processes of fairings from the optical ceramics haven't been sufficiently investigated in the form of semi-spherical shells with the oncoming supersonic airflow, as well as the complex influence of the heat-physical characteristics of ceramics material haven't been studied (volume heat -capacity and thermal conductivity coefficient) under the conditions of supersonic airflow on temperature distribution and thermoelastic stresses in the zones of maximum external thermal actions. This paper contains developed mathematical heating models of fairings in IR-devices by supersonic airflow, that encounter temperature dependencies of thermophysical properties of optical materials. Calculations of temperature distribution and thermoelastic stresses in the fairing are carried out. Critical values of airflow velocities of the fairing and the time of its thermal influence are determined, exceeding of which leads to destruction of the fairing and the failure of IR -devices. It is determined that the distribution of temperature along the surface of the fairing most essentially depends on the flow mode: temperature maximum is near its front point for laminar mode, and for turbulent mode temperature maximum is shifted along the surface of the fairing at a distance corresponding 18…22 deg. It is shown that the thermoelastic stress in the zones of maximum external thermal action in the thickness of the fairing is distributed as follows: squeezing stresses occur on the fairing surface and in its surface layers, while in the lower part of the fairing and in its adjacent layers these are stretching stresses; thus for turbulent flow mode exceeds its value for laminar mode by 5…6 times. The interdependence of critical velocity values of the fairing airflow and the times of its thermal influence, exceeding of which leads to the destruction of the fairing; thus, for the turbulent flow mode destruction of the fairing occurs near its surface, and for laminar mode destruction of the fairing is no longer observed.