RU2534362C1 - Method of thermal loading of aircraft structures made from nonmetallic materials - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method of thermal loading of aircraft structures from nonmetallic materials involves zone heating of an item and measurement of the temperature. Zone heating of the item is carried out by contactless transfer of energy by alternating magnetic field of medium frequency generated by an inductor to the intermediate heating element made from ferromagnetic material located on the item surface.

EFFECT: improved accuracy of performing the aircraft test programmes.

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Description

The invention relates to the field of mechanical engineering and the aerospace industry and can be used to test the design of aircraft and their units (head fairings) from non-metallic materials for thermal, as well as complex thermal and vibration and thermal vacuum effects during experimental testing in ground conditions, as a method reproducing aerodynamic thermal effects.

Currently, the reproduction of aerodynamic heating is carried out in various installations: wind tunnels, ballistic installations, plasma installations, stands based on direct-flow jet engines [Materials and coatings in extreme conditions. A look into the future: In 3 vols. - Vol. 3. Experimental studies / Yu.V. Polezhaev, S.V. Reznik, A.N. Baranov et al. Ed. Yu.V. Polezhaeva and S.V. Reznik. - M.: Publishing House of MSTU. N.E. Bauman, 2002. - 264 p.: Ill.]. The disadvantages of the methods is the high cost of testing and, as a consequence, the limitation of the use of aircraft structures in ground testing.

One of the most common ground tests in practice is radiation heating stands.

The closest in technical essence and the achieved result is a method of thermal loading of rocket fairings from non-metallic materials - Patent RU 2456568 C1, 20.07.2012. The method includes zone heating of the product and temperature measurement, characterized in that the product is heated by contacting the heater with the outer surface, and the temperature distribution along the height of the cowl is determined by the electrically conductive sectors of the heater of different thicknesses connected in series to the electric circuit.

The main disadvantage of this method is that the process of transferring energy to the heater is carried out by contact using current-carrying buses located on the heater, which creates structural difficulties in the process of carrying out thermal loading, and also reduces the accuracy of the test programs.

The aim of the invention is the structural simplification of the process of transferring energy to the heater and increasing the accuracy of the test programs when simulating in real-world conditions of real heat exposure due to contactless transfer of energy to the heater.

The goal is achieved by the fact that the proposed method of thermal loading of aircraft structures made of non-metallic materials, including zone heating of the product and temperature measurement, characterized in that the zone heating of the product is carried out by contactless energy transfer by an alternating magnetic field of a medium frequency generated by an inductor to an intermediate heating element made of ferromagnetic material located on the surface of the product.

The authors experimentally established that under the influence of a mid-frequency magnetic field (2 ÷ 3 kHz), due to magnetic resistance, intense heating of the intermediate heating element made of ferromagnetic material occurs, from which heat transfer of the product is carried out by heat transfer. The rest of the test rig is made of non-ferromagnetic material, and when exposed to an alternating magnetic field of medium frequency, it does not significantly heat up. Due to this effect, energy losses due to heating of the test rig are excluded.

The method illustrates the diagram shown in the drawing. Thermal loading of the non-metallic product 1 is carried out by transferring heat from the intermediate heating element 2, heated in an alternating magnetic field generated by the inductor 3. To reduce heat loss and direct the flow of heat energy to the product, the intermediate heating element is insulated from the outside with special heat-insulating material 4. Based on from the conditions of thermal loading, the inductor and the intermediate heating element are made in various configurations and disposed of They are scented both outside and inside the heated product.

The proposed method is implemented as follows. For a given distribution of heat flux density along the height of the product, the design is conditionally divided into zones with a given heat flux density. Further, for each zone, an intermediate heating element is made of a ferromagnetic material with a surface equidistant to the surface of the product in the corresponding heat loading zone. The intermediate heating element together with the product is placed in an alternating magnetic field of medium frequency generated by an inductor, in which it is contactless heated. Zone heating of the product is carried out by heat transfer from the intermediate heating element and the temperature in each zone is measured. The structural, electrical and energy parameters of the inductor - intermediate heating element system are set based on the thermal loading mode and the specifics of the task to be performed.

To calculate the distribution of heat flux density over the height of the product, the heating element is divided into i zones (see drawing).

The heat flux density q _i in the i-th zone can be determined using the formula:

$$q_i=\frac{{\left(w\cdot I\cdot k_{\mathrm{from}\mathrm{at}}\right)}^2\cdot \sqrt{{\rho }_i\cdot {\mu }_i\cdot f\cdot }{F}_f\cdot \cos \alpha }{\pi \cdot \left(2r_i+\Delta h_i\cdot tg\alpha \right)\cdot \Delta h_i};\text{(one)}$$

where w is the number of turns of the inductor falling on the i-th zone;

I is the current strength in the inductor;

k _sv is the coupling coefficient of the inductor-heater system;

ρ is the electrical resistivity;

µ is the relative magnetic permeability;

f is the current frequency in the inductor;

F _f - correction function;

Δh _i is the height of the i-th zone;

r _i is the radius of the i-th zone;

α is the angle of inclination of the i-th zone to the vertical axis.

Formula (1) is derived by solving the system of differential equations of the electromagnetic field

, $$\begin{array}{l}rot\overline{H}=\overline{J}+\frac{\partial \overline{D}}{\partial t},\\ rot\overline{E}=-\frac{\partial \overline{B}}{\partial t},\\ div\overline{H}=0\\ div\overline{E}=0;\end{array}\}\text{(2)}$$

,

where B is the magnetic induction;

D is electric induction;

H is the magnetic field strength;

J is the conductivity current density;

E is the electric field strength;

subject to the following assumptions:

- the electromagnetic field changes according to a sinusoidal law;

- since in metals the bias current is much less than the conduction current, for conductors

, а для проводящих сред $$\overline{J}=0$$

. $$\frac{\partial \overline{D}}{\partial t}=0$$

, and for conductive media $$\overline{J}=0$$

.

The proposed method allows to simplify the process of energy transfer to the intermediate heating element, to increase the accuracy of the test programs and reduce energy costs for their implementation. The method can find wide application in conducting thermal, as well as complex thermal vibration and thermal vacuum tests during experimental testing in ground conditions of aircraft structures and their assemblies of non-metallic materials with various surface shapes.

Claims (1)

The method of thermal loading of aircraft structures made of non-metallic materials, including zone heating of the product and temperature measurement, characterized in that the zone heating of the product is carried out by non-contact transfer of energy by an alternating magnetic field of medium frequency generated by the inductor into an intermediate heating element made of ferromagnetic material located on product surface.