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Determination of distributions of temperature and thermoelastic stresses through the thickness of optical fairings of IR-devices in the conditions of intense external thermo-influences

І. Yatsenko, Valentyn Gordienko, Oksana Kyrychenko, Vyacheslav Vaschenko, Valentin Tsybulin

Abstract

By this time the processes of heating of optical ceramics fairings in the form of hemispherical shells by oncoming supersonic air stream are insufficiently investigated, and also integrated effect of thermophysical characteristics of ceramics material (volumetric heat capacity CV(T) and thermal conductivity coefficient l(T)) under supersonic blowing by air flow on the distribution of temperatures and thermoelastic stresses in zones of maximum external thermo-influences is not studied. This work is devoted to mathematical modeling of the process of fairings heating by supersonic gas flow and determination of critical values of its parameters (flow rate, its duration, mode of flow), the excess of which leads to their destruction and IR-devices failure. Mathematical model for heating infrared devices fairings by supersonic air stream, taking into account temperature dependence of thermal-physical properties of optical materials, is developed. The calculations of temperature distributions and thermal-elastic stresses in fairings are performed. Critical velocity of blowing air flow of the fairing and time of heat exposure, the excess of which leads to fairing destruction and IR-devices failure are calculated. It is established that temperature distribution along fairing surface most significantly depends on flow regime: for laminar regime the maximum temperature is close to its front critical point, and for turbulent regime the maximum temperature is shifted along fairing surface at the distance corresponding to q max = 17…210 . It is shown that thermo-elastic stresses in zones of maximum external thermo-influences on fairing thickness are distributed as follows: on fairing surface and in its surface layers compressive stresses take place (s < 0 , max s reaches the values of 108 ... 3,5·108 N/m2 ), and on fairing underside and in its adjacent layers tensile stresses are present (s > 0 , max s reaches the values of 0,5·108 to 1,5·108 N/m2 ); however, for turbulent regime the flow exceeds its value for laminar regime in 4...5 times. Interdependences of critical values of the velocity of fairing blowing by air flow and the time of its exposure to heat, the excess of which leads to fairing destruction, are established; while for turbulent flow regime the fairing destruction occurs near its surface, and for laminar regime the fairing destruction is no longer observed

Keywords:

thermal-elastic stresses, optical fairing, thermal influence

Retrieved from Volume 21, No. 4, 2016

Pages 20-27

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Suggested citation

Yatsenko, I., Gordienko, V., Kyrychenko, O., Vaschenko, V., & Tsybulin, V. (2016). Determination of distributions of temperature and thermoelastic stresses through the thickness of optical fairings of IR-devices in the conditions of intense external thermo-influences. Bulletin of Cherkasy State Technological University, 21(4), 20-27.