The effect of heat insulation on the cooling requirements of the internal structure of high-speed vehicles

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Virginia Polytechnic Institute


The present thesis project consisted of two parts. First, a general method for determining the transient skin temperatures of bodies during high-speed flight was developed. The governing differential equation was presented for this purpose, giving the fundamental relations between the transient skin temperature and flight history. The determination of all pertinent parameters in the equation was discussed, and the Runge-Kutta numerical method of integration was used to obtain the solution. The method was employed to compute the time history of the skin temperatures for several hypothetical flight plans, and the results presented in the form of graphs. For the Mach number and altitude range investigated, the maximum skin temperature obtained was approximately 2200 °R and was found to be largely independent of the type of trajectory.

The second portion of the project consisted of determining the effect of heat insulation on the cooling requirements of the internal structure of a high-speed vehicle. The governing equation for heat conduction through an isotropic solid was developed, and then modified to account for nonhomogeneous materials. The initial and boundary conditions for the governing equation were specified, and the equation solved by the method of finite-differences. The temperatures obtained, the first portion the thesis, were used as the outer surface temperature variation of the insulation, and the time history of the inner surface temperature of the insulation (for several thicknesses) was calculated. To make the problem as general as possible, the results were presented in terms of the thermal diffusivity of the insulating material. For illustrative purposes, an example problem was worked using rock wool as the insulating material. It was found that, by using one-half inch of this insulating material, the maximum temperature obtained by the internal structure was less that 5 percent of the skin temperature. Thus, it was concluded that the increase of the temperature of the internal structure of a high-speed vehicle during a limited time of flight, can be held to structurally permissable values by the use of heat insulation placed between the skin and the internal structure of the vehicle.