COMPARISON OF HEAT EXCHANGE PROCESSES WHEN CONJUGING BODIES BY HYPERSONIC FLOW

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The Turkish Online Journal of Design, Art and Communication - TOJDAC ISSN: 2146-5193, March 2018 Special Edition, p. 465-474

Submit Date: 09.01.2018, Acceptance Date: 23.02.2018, DOI NO: 10.7456/1080MSE/155 Research Article - This article was checked by Turnitin

465

COMPARISON OF HEAT EXCHANGE PROCESSES WHEN CONJUGING

BODIES BY HYPERSONIC FLOW

A A Chernykh, A I Sharapov, A V Peshkova and Y V Shatskikh

Department of industrial heat power engineering, LSTU, Moskovskaya street 30, Lipetsk 398600, Russian Federation

ABSTRACT

the results of simulation of the temperature distribution on the flying vehicles surfaces (FV), which are streamlined by a hypersonic oncoming flow, are presented in the work. A comparison is made of the temperature fields distribution for various models that are subjected to the action of an oncoming flow with different Mach numbers at different heights.

Keywords: heat exchange, conjuging bodise, hypersonic flow INTRODUCTION

The purpose of this work is to demonstrate the effectiveness of the developed software with respect to the flight of aircraft moving with supersonic speed. This problem was solved with the help of a developed set of programs that allows specifying the boundary conditions of various types: the atmosphere parameters, the sample metal of the hypersonic flying vehicles (HFV), the initial flight conditions, the oncoming flow parameters, etc. In this work, there were considered and presented the results, which will concern the modeling of different HFV by geometry.

The main task that is put before the aerodynamics of hypersonic stream is to develop materials that would withstand sufficient pressure from the oncoming stream, as temperatures on the FV surface can range from several hundred to several thousand degrees, depending on the altitude of the flight. Therefore, the software development is conditioned by practical applications, which makes research of this problem very clear. Simulation of various heat exchange processes in the program will allow us to perform complex mathematical calculations without resorting to quite expensive experimental studies. The models considered in this work made it possible to clearly show the heat propagation process over the surface of various samples. The model of gas flow process of HFV is shown in Figure 1. The main interest is the heat pressure on the blunt bodies surface (type No. 1), as it is shown in Figures 2 and 3.

Shock wave

Figure 1. The model of gas flow process of HFV

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466 Figure 2. Distribution of the temperature field over the FV surface (type No. 1) made of titanium at a

temperature of Т_! = 750 ° C, at М_! = 5 at an altitude of 30 km, at 102 seconds

Figure 3. Distribution of the temperature field over the FV surface (type No. 1) made of titanium at a temperature Т_! = 750 ° C, at М_! = 5 at an altitude of 30 km, at 180 seconds

In this case, it is worth noting that aircraft type №1 is moving in the air without taking into account any sublimation or ablation processes. The formation of various nitrogen oxides and oxides of various metals was also not taken into account, since the chemistry of such processes has not yet been fully studied. One type of heat-resistant coating that is used in conjunction with composite materials is an epoxy or organosilicone resin. When applying such a resin to the HFV surface under the influence of a continuous thermal load, gaseous pyrolysis products are formed. The process of pyrolysis with the formation of phenolic compounds proceeds in parallel with physico-chemical transformations on the composite materials surface. Figures 4-6 show the results of heat transfer modeling at Т_! = 3000 ° C for titanium HFV sheathing at various flight times. It should be noted that at sufficiently high thermal pressure, the heat-resistant aircraft coating is carried away, which is accompanied by the various radicals formation, for

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467 example NO . At a sufficiently long flight time, on the order of 300 s (Figure 6), high temperatures of the order of 2860 ° C are achieved practically on the entire FV surface.

Figure 4. Distribution of the temperature field over the HFV surface (type No. 1) made of titanium at a temperature Т_! = 3000 ° C, at М_! = 15 at 142 seconds

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468 Figure 5. Distribution of the temperature field over the HFV surface (type No. 1) made of titanium at a

temperature Т_! = 3000 ° C, at М_! = 15 at 184 seconds

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469 Figure 6. Distribution of the temperature field over the HFV surface (type No. 1) made of titanium, at a

temperature Т_! = 3000 ° C, at М_! = 15, at 302 seconds

When working with such high temperatures, the equations of hydrodynamics (kinetic equations) for gases and plasmas are derived in two ways: phenomenological and statistical. The first - takes into account all known equations of energy, mass, momentum. The second - takes into account the molecular-kinetic concepts of matter and is used to derive the media to which the corresponding kinetic equations can be applied.

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470 In HFV flight modeling in the upper atmosphere, the data given in the work [2] were also used. These data are indicated in Table 1.

Н, km 𝑉_!, m/s М_! 𝜌_!, kg/𝑚^! Т_!, К

50 4977 15 1,08∙ 10^!! 274

60 6382 20 3,32∙ 10^!! 253,4

70 7423 25 9,27∙ 10^!! 219,1

80 6818 25 2,09∙ 10^!! 184,9

When designing the airframe, it is necessary to have information about the thermochemical stability of the materials used and the recombination rates, which can be obtained on the basis of experiments [3] in high- temperature gas flows (temperature on the sample surface Т_! = 1000-10000 ° C). It is already clear from Figures 4 and 6 that after 142 and 302 seconds the temperature approaches 500-700 ° C within the sample, which is inadmissible in the electronics operation. Such temperatures inside the HFV make its control short-term, and the flight process - unpredictable, which imposes certain requirements for thermal protection of such aircraft.

Based on all of the above, it should be noted that the correct interpretation of the data obtained with the help of theoretical calculation ([4-5]) using the methods given above and the data obtained by the experimental method are possible only on the basis of a detailed account of heterogeneous catalytic reactions on different types of heat-resistant coatings.

Also heat exchange is simulated on another HFV configuration surface - Type No. 2, made of titanium.

Figure 7. Distribution of the temperature field over the HFV surface (type No. 2) at a temperature Т_! = 1600 ° C, with М_! = 10 at 30 seconds

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471 Figure 8. Distribution of the temperature field over the HFV surface (type No. 2) at a temperature Т_! =

1600 ° C, with М_! = 10 at 90 seconds

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1600 ° C, with М_! = 10 at 180 seconds

When this model is calculated, a "vortex" appears on the surface, which begins to be less pronounced with a further increase in heat flux (see Figures 7-9). The main data used in this modeling are as follows: the heating area or influence of the boundary layer on the aircraft is 75% of the model length, at the leading edge Т_! = 1600 ° C, and the number М_! = 10. When constructing a calculation grid, the methods given in [6] were used. There were not applied various physicochemical processes of dissociation and recombination in this model, because the accounting of such processes is mainly carried out in the interval of Mach numbers of 15<M <25.

Since there are a sufficient number of monographs on the topic of studying the HFV thermal pressure, we do not undertake to introduce any additional quantities, because the data of many authors differ by more than an order of magnitude in the heat exchange and kinetics of the reaction in the temperature range Т_! = 2000-20000 ° C.

At hypersonic flight speeds, the aerodynamic characteristics of the entire aircraft and its individual elements will significantly affect the power plant characteristics, since the interaction of the complex geometry configuration with a hypersonic flow leads to the emergence of intense interacting shock waves.

Therefore, an important conceptual task of HFV designing should be integration into a unified system of fuselage, wings and an engine. In this case, it is necessary to limit the allowable range of attack angles and the attachment area of the leading-edge shock. From the point of view of heat exchange, the power plant design should also be made of sufficiently refractory material to avoid the effect of additional thermal pressure.

Let's consider one more HFV model of "glider" type (type № 3). This model calculation was carried out under the condition that the front wall temperature Т_! = 1500 ° C, and the number М_! = 10, and the HFV is made of titanium. The corresponding simulation is shown in Figures 10 and 11. It can be noticed that an area of sufficiently high temperature is formed at the edge of the wing bending.

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1500 ° C, the number М_! = 10 at 365 seconds

Figure 11. Distribution of the temperature field over the HFV surface (type No. 3) at a temperature Т_! = 1500 ° C, number М_! = 10 at 702 seconds

Such formation is associated with a high-enthalpy effect of the boundary layer, which has time to catch the bending at the beginning of the wing. In Figure 10 there is an area of the order of 1100 ° C, and in 15 it is an area on the order of 1400 ° C. But already from this "glider" simulation it is evident that it will be preferable from all the models above, since at 700 seconds the area at 1400 ° C does not cover the entire surface of the aircraft fuselage.

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474 CONCLUSION

In the course of the simulation, results were obtained for the various HFV forms. The obtained results analysis allows us to conclude that the most suitable hypersonic flying vehicle model in terms of heat exchange is a glider-type model.

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