Heat flow balance accounting on the aircraft outer surface

Аuthors

Egorov I. A.

e-mail: egorov_ff@rambler.ru

Abstract

When flying at high speeds, the surface temperature reaches high values. In this regard, is the role of radiant heat flow in the heat exchange process increased. There is a need for more accurate recording.

This article is on the radiant heat flow accounting by numerical integration of the aircraft construction heating process directed.

The task is reducing to calculation about the skin one-dimensional heating (along thickness). The heat equation is recorded in the central finite differences form. As a result is create the algebraic equations system. For the boundary points used equations of boundary conditions. For the outer surface used the balance equation of heat flow.

The heating process is calculated numerically by the method of numerical integration. The nonlinearity of the dependence of radiant heat flow on the surface temperature is eliminated by using the value of the surface temperature at the previous integration step. Investigated the validity of this approach under various intensity of heat. It is shown that in some cases it is possible to obtain divergent process.The scheme formulated solutions to ensure the sustainability of the process and increase its accuracy.

The calculation is performed in the following sequence:

1. Sets the initial value of the surface temperature is equal to the value of the surface temperature for the previous step of time integration.

2. For this value of the surface temperature calculated heat flux radiation and determines a value of heat transfer coefficient.

3. Calculation of the temperature field of a multilayer structure, which defines the new value of the surface temperature for a given step of the time integration.

4. Inaccuracy of specifying the value of surface temperature.

5. If the error in determining the surface temperature does not exceed a predetermined value, the process moves to the next stage of the calculation.

6. If the error in determining the surface temperature exceeds the specified value, restores the original temperature field and the adjustment values of the surface temperature by a given amount. The adjustment is made in the direction of increasing or decreasing values of the surface temperature depending on the sign of the increment of the magnitude of radiant heat flux.

Proposed scheme solution allows to properly take into account radiant heat flux for the intensely hot designs.

Conclusions:

1. Determination of radiant heat flux using the temperature at the previous step of time integration is an effective way of taking into account the boundary conditions for the numerical calculation of heating of the aircraft in flight.

2. To ensure stability of the calculation process, it is necessary to control the accuracy of determining the surface temperature at each step of time integration and, if necessary, to clarify the obtained values.

3. It is advisable to use high values of accuracy parameters (the acceptable accuracy of determining the surface temperature 0.5%, step approach temperature of 2°) , which will provide not only the stability of the calculation and the high accuracy of the results, but also decrease the time of calculation.

Keywords:

temperature field, numerical integration, aircraft, outer surface, boundary condition, radiant heat flow

References

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