RU2452669C1 - Method for thermal shielding aircraft nose - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method for thermal shielding the nose of aircraft involves performing the following operations: gas coolant is fed through perforated holes in the region of interaction of the nose with the circumfluent flow and turbulent vortex, arising in the high-gradient zones of interaction of elementary jets of the coolant gas and the incoming high-temperature gas stream is fed while applying periodic tangential vibrations with intensity I in the range 1.75 × 10⁵ ≤ I ≤ 39.2 × 10⁵ kg·grad²/s³m². The tangential vibrations are applied in a plane which is perpendicular to the axis of symmetry of the surface of the nose of the aircraft. The frequency of the vibrations is in the range 5 ≤ f ≤ 25 Hz and amplitude of the vibrations is in the range 1 ≤ A ≤ 9 angular degrees.

EFFECT: high efficiency of cooling the nose of aircraft.

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Description

The invention relates to aviation and space technology, and in particular to methods of cooling the head elements of the structures of aircraft (LA). At the entrance of an aircraft with hypersonic speeds into the dense layers of the atmosphere, its head part is subjected to intense heat loads. An increase in the descent speeds of modern aircraft leads to an increase in the requirements for thermal protection.

Hydrodynamic methods are known for protecting the aircraft surface from the effects of high-temperature gas flows, for example, the method of porous cooling, when a cooler gas is injected into the intensive heating zone (boundary layer) through a surface made of porous materials (1. Ramsey, Golypteyn, Interaction of an injected heated jet with the main stream. / Heat Transfer. T.93, No. 4, 1971, p. 41-50).

The disadvantage of this method is that porous heat-shielding materials can not withstand large thermal loads, can be destroyed.

There is also known a method of thermal protection of the surfaces of the head part of an aircraft, when it is cooled using liquid or gaseous refrigerant. The casing is perforated, and the refrigerant is brought to the inner surface of the casing and is blown through the perforation into the boundary layer. (2. Fundamentals of heat transfer in aircraft and rocket technology. // Edited by V.K. Koshkin, M .: Mechanical Engineering, 1975)

The disadvantage of this method is the low strength and temperature characteristics of the material, since through perforation turbulizes the incoming flow, which increases the heating rate of the head of the aircraft. Ultimately, the protection material is destroyed.

Closest to the proposed solution is a cooling method using a gas cooler. The method is based on blowing gas into the impact zone of the incident gas flow (3. RF Application, No. 96118303, aircraft, publ. 12/20/1998). The method selected for the prototype.

A well-known aircraft uses cooling based on the injection of a cooler gas into the zone of influence of the incident flow of high-temperature gases on the aircraft head. The gas cooler is supplied under pressure towards the high-temperature flow through the through holes in the aircraft shell.

A significant disadvantage of the method used in the prototype is the high degree of turbulization of the stream in the area of mixing hot and cold gas, which reduces the cooling efficiency of the head of the aircraft. This drawback should be addressed.

The present invention is based on the task of increased cooling efficiency of the head part of launching aircraft by exposing the surface of the cooled structure to periodically repeated vibrational influences over time. The problem is solved in that, in addition to the main features of the prototype method, turbulent eddies that occur in high-gradient zones of interaction of elementary jets of a gas cooler and an incident high-temperature gas flow are suppressed, acting on them with periodic tangential vibrations of intensity I in the range of 1.75≤ I≤39.2 kg · deg ² / s ³ m ² , imposed in a plane perpendicular to the axis of symmetry of the surface of the head of the aircraft. Range I characterizes the frequency and amplitude of vibration of the surface to be protected. The essence of the method is illustrated by drawings (figure 1, figure 2, figure 3).

Figure 1 shows a physical model of the flow pattern in the vicinity of the shell of the head part when the gas cooler is injected through round openings towards the high-temperature incoming flow. Figure 2 shows the change of the laboratory installation that implements the claimed method. The high-temperature free-stream 2 and the gas-cooler stream are perpendicular to the shell of the head part 1, ω is the rotational speed of the motor shaft, f is the vibration frequency, d ₁ and d ₂ are the diameter of the shell and the diameter of the holes for injecting the gas-cooler.

, при вибрациях (кривая а - расход газа-охладителя 0,3·10^-4 кг/с; б - расход газа-охладителя 0,41·10^-4 кг/с, в - расход газа-охладителя 0,73·10^-4 кг/с), от интенсивности тангенциальных вибраций I. Здесь q₊, q_- - плотность тепловых потоков при наличии (+) и отсутствии (-) вибраций.Figure 3 shows the dependence of the relative heat transfer function

, with vibrations (curve a - flow rate of the cooler gas 0.3 · 10 ^-4 kg / s; b - flow rate of the gas cooler 0.41 · 10 ^-4 kg / s, c - flow rate of the gas-cooler 0.73 · 10 ^-4 kg / s), from the intensity of tangential vibrations I. Here q ₊ , q _- is the density of heat fluxes in the presence of (+) and absence (-) of vibrations.

The numbers in the figures indicate: 1 - the shell of the head in the form of a truncated cone; 2 - high temperature flow; 3 - gas cooler; 4 - stagnant flow areas; 5 - zones of the main sections of elementary jets; 6 - zone closure of elementary jets; 7 is a mixing region of a supplied coolant gas and a free flow.

The method is implemented as follows.

The surface to be protected is subjected to periodic tangential vibrations in a plane perpendicular to the axis of symmetry with a certain frequency f. In this case, the gas cooler 3 in the form of elementary jets 5, leaving the protected wall, forms a mixing region 7 with the free stream 2. The free stream is displaced and the boundary layer is “diluted” near the surface of the aircraft head. The condition for the displacement of the incoming flow is the early closure of elementary gas jets 5. Due to this, a continuous continuous oncoming gas barrier is created in front of the incident stream. However, the presence of stagnant regions 4 and the remoteness of the zones of closure of the elementary jets 6 lead to the appearance of hydrodynamic instability, the appearance of large-scale gas pulsations. The pulsations carry gas from the incident high-temperature flow 2 to the protected surface of the head part 1. As a result, heat transfer is intensified. In order to eliminate turbulent eddies near the surface and provide conditions for early closure of elementary jets 5, it suffices to act on the surface by tangential periodic vibrations in a plane perpendicular to the axis of symmetry of the surface with a frequency f varying in the range 5≤f≤25 Hz. The inertial force arising due to tangential vibration acting on the jets leads to their earlier closure, high-gradient flow regions are destroyed, and the mixing region becomes uniform, without the formation of large-scale pulsations. The heat exchange between the incoming flow and the head part of the aircraft is reduced, which increases the cooling efficiency.

At a vibration frequency f <5 Hz, attenuation of heat transfer is not observed. At frequencies f> 25 Hz, the operational characteristics of launching aircraft may be violated. This feature does not exclude the possibility of selecting a frequency for specific designs.

It is advisable to take into account the amplitude A of tangential vibrations, which affects the efficiency of heat transfer. Detailed calculations [4] show that heat transfer attenuation is performed when amplitude A changes in the range 1 ° ≤A≤9 ° (bulky calculations are omitted). At A <1 °, heat transfer attenuation is not observed. At A> 9 °, unwanted vibrations occur due to the resonant characteristics of the device.

Example. The proposed cooling method is tested on the model of the shell of the aircraft head part (Fig. 2), made in the form of a perforated truncated cone. Tangential vibrations were set by converting the rotational motion of the shaft of the electric motor 8 into oscillatory motion around the axis of the model 1 using the rocker arm 9 and the rod 10. The frequency of tangential vibrations f and amplitude A are controlled by changing the rotation speed of the motor shaft ω and the length of the rocker arm 9. Shell 1 is made of stainless steel (wall thickness δ = 1.5 · 10 ^-3 m). The dull diameter, which is affected by the oncoming gas stream 2, was chosen d ₁ = 1.9 · l0 ^-2 m, the diameters of the round holes 11 for blowing the gas-cooler were chosen d ₂ = 1 · l0 ^-3 m. High-temperature gas stream 2 modeled by a plasma torch EDP-104A / 50 (not shown). Free flow parameters: temperature 3600 K, heat flux density q = (0.02 ÷ 6.2) · 10 ⁶ W / m ² , flow rate G = (0.9 ÷ 2.25) · 10 ^-3 kg / s, flow rate 60 m / s. Air with a temperature of (300 ÷ 310) K is used as a cooler gas. Oncoming flow and heat and mass transfer parameters are determined by known methods using thermocouples, hot-wire anemometers, pneumatic probes, rotameters. In all experiments, the parameters of the oncoming flow and the blown gas-cooler do not change in time. The frequency of tangential vibrations f was chosen from the range from 5 to 25 Hz.

Figure 3 shows the test results. Here Ψ is the relative heat transfer function equal to Ψ = (q ₊ -q _- ) / q _- , where q ₊ , q _- are the density of heat fluxes acting on the model, respectively, in the presence of (+) and absence of (-) vibrations. The values of the intensity of vibrations I are indicated on the horizontal coordinate axis. Here, the value of I varies in the range 1.75 · 10 ⁵ ≤I≤39.2 · 10 ⁵ , the dimension I - [kg · deg ² / s ³ m ² ] takes into account the amplitude, and the vibration frequency [4].

From the obtained results on the influence of tangential vibrations on heat transfer, the following was noted. At relatively low gas flow rates of the cooler (curve a), the effect of vibration on heat transfer is negligible. With an increase in the flow rate of the cooler gas through the model openings, the influence of tangential vibrations on heat transfer manifests itself to a greater extent (curves 6, c).

It should be noted that for a value of I <1.75 · 10 ⁵ [kg · deg ² / s ³ m ² ], the relative heat transfer function is Ψ → 0. In this case, the heat flux q of high-temperature gases practically without interference affects the surface of the tested model. Similarly, at I≥39 · 10 ⁵ [kg · deg ² / s ³ m ² ] the values of the function Ψ also begin to decrease. In this case, the increasing intensity of the tangential vibrations will enhance the mixing of gases in the mixing region 7 (Fig. 1), which intensifies the process of heat exchange between mixed gases with high temperature and the test surface. This will lead to an increase in the heat flux density q, respectively, the surface temperature will increase.

In the graph of FIG. 3, the horizontal axis corresponds to heat and mass transfer without vibrations. An analysis of the curves of Ψ from I shown in Fig. 3 shows that the presence of tangential vibrations acting on the model of the aircraft’s head makes it possible to reduce the influence of the heat flux of high-temperature gases on the model by up to 27% compared to heat exchange without vibrations.

From the above example it is seen that the claimed method of thermal protection of the aircraft head can be implemented in practice, which indicates the compliance of the invention with the criterion of "industrial applicability". The cooling of the head of the aircraft with a combination of the claimed features is not obvious, which indicates that the technical solution meets the criterion of "inventive step". Currently, work is underway to create a device for implementing the method in natural conditions.

Information sources

1. Ramsey, Holstein, Interaction of an injected heated jet with the main stream. / Heat transfer. T.93, No. 4, 1971, p.41-50.

2. The basics of heat transfer in aircraft and rocket technology. // Ed. V.K. Koshkina, Moscow: Engineering, 1975

3. Application of the Russian Federation, No. 96118303, 1996

4. Golovanov A.N. Heat transfer of an axisymmetric blunt body in a gas stream in the presence of injection of a cooler gas through round holes and vibrational disturbances. // IFZh, T.63, No. 2, 1992. S.194-198.

Claims (3)

1. The method of thermal protection of the head of the aircraft, including the supply of gas cooler under pressure through the round holes of the permeable portion of the surface of the head of the head towards the incident high-temperature gas flow, characterized in that tangential vibrations are applied to the surface of the head in a plane perpendicular to the axis of symmetry I, selected in the range of 1.75 × 10 ⁵ ≤I≤39,2 × 10 ⁵ kg · deg ² / s ³ m ² . 2. The method according to claim 1, characterized in that the frequency of tangential vibrations f is selected in the range of 5≤f≤25 Hz. 3. The method according to claim 1, characterized in that the amplitude of the tangential vibrations And choose in the range of 1≤A≤9 angular degrees.

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