CN105404722B - A kind of method analyzed projectile impact and Inerting Aircraft Fuel Tanks are influenced - Google Patents

Abstract

A method for analyzing the impact of projectile impact on aircraft fuel tank inertness is an amendment to the existing aircraft fuel tank inert model: according to the initial conditions, calculate the motion state parameters after the projectile penetrates the fuel tank wall, and then analyze the projectile breakdown Analyze the energy change behind the fuel tank wall, analyze the heat transfer of the projectile during the movement in the fuel tank and calculate the fuel vapor volume increased by the fuel droplet evaporation, and calculate the time when the projectile penetrates the fuel tank wall and enters the gas phase space of the fuel tank The amount of air in the external environment brought in, and finally according to the above analysis, the existing inertization model is corrected. The invention can be used to analyze the influence of projectile parameters and environment parameter changes on the gas concentration in the gas phase space in the combat environment, and then determine whether the fuel tank is combustible.

Description

A method for analyzing the effect of projectile impact on the inerting of aircraft fuel tanks

technical field

The invention relates to the field of vulnerability reduction design of aviation combat aircraft, in particular to a fuel inerting analysis method considering projectile impact.

Background technique

Aircraft combat survivability is the ability of aircraft to avoid or withstand man-made hostile environments, and it is divided into two research areas: sensitivity and vulnerability. Vulnerability is defined as the ability of a combat aircraft to withstand the threat of man-made hostile environments in a combat state. Given the vulnerability of aircraft components is an important task in survivability assessment, it should be considered in the early stage of aircraft design. It provides guidelines for effectively improving aircraft survivability, and puts the main design tasks on highly vulnerable components in a targeted manner, so as to achieve efficient and optimal design of aircraft survivability.

The higher the vulnerability of the aircraft, the easier it is to be killed when it is hit, and the more it will reduce the ability of the aircraft to complete the mission. The aircraft fuel tank is used to store the fuel consumed by the power system to maintain the flight of the aircraft. Military aircrafts mostly adopt the large-area layout of the wings and the fuselage, so the exposed area of the fuel tank usually accounts for more than 50% of the whole aircraft, which is easy to use on the aircraft. One of the most destructive components. When a military aircraft is engaged in combat, it is very likely to be hit by threats such as projectiles or missile fragments. When the threat hits the fuel tank of the aircraft, the main killing mode is combustion and explosion, which is an important cause of aircraft damage.

Fuel inerting technology is an effective measure to prevent combustion and explosion suppression. By injecting nitrogen-rich gas into the fuel tank, the oxygen content in the fuel tank is lower than the combustion limit to prevent combustion from occurring. The current fuel tank inerting technology is divided into two types: fuel washing and gas phase space washing. Fuel washing is to pass inert gas into the fuel through a small nozzle installed at the bottom of the fuel tank to replace the dissolved oxygen in the fuel, thereby reducing the concentration of dissolved oxygen in the fuel, so that the amount of oxygen released during the flight will be small Or if there is no precipitation, the oxygen concentration in the gas phase space in the fuel tank will be maintained within a safe range. Gas phase space flushing technology is to directly pass inert gas into the gas phase space of the fuel tank to dilute the oxygen in the original gas, so as to achieve the purpose of reducing the oxygen concentration in the gas phase space. At present, due to the battlefield environment where military aircraft are located, most of the two technologies are used in combination to reduce the vulnerability of the fuel tank and improve the survivability of the aircraft on the battlefield.

For penetration effects inerting, mainly occurs in military aircraft, therefore, the inerting mainly concerned in this paper is fuel scrubbing. During the fuel washing process, the nitrogen-rich gas is injected into the fuel through the nozzle at the bottom of the fuel tank, forming a large number of tiny bubbles. There is a concentration gradient between the dissolved oxygen and nitrogen in the fuel and the nitrogen-rich gas in the bubbles, and the original balance is destroyed. Part of the dissolved oxygen is precipitated from the fuel, as shown in Figure 1. The basic flow of the existing inertization analysis is shown in the left figure in Figure 2, and the basic inertization schematic diagram is as follows.

In the first step, the fuel in the fuel tank is taken as the research object to determine the flow rate of each component of nitrogen-enriched gas (NEA). Taking △t as the time step, and △t is small enough, it can be considered that the state parameters of each component remain constant during this time period. The mass of oxygen and nitrogen flowing into and out of the fuel tank within △t follows the law of mass conservation,

In the formula, O represents oxygen, N represents nitrogen, subscript F represents Fuel, subscript U in Fig. 1 represents Ullage, 1 represents the initial time within the Δt time period, and 2 represents the end time.

In the second step, according to the partial pressure of oxygen and nitrogen in the fuel and the ostwald relationship, the amounts of dissolved oxygen O _F1 and O _F2 and the amounts of nitrogen N _F1 and N _F2 in the fuel at the initial and final moments are obtained. The ostwald relation is,

In the formula, β is the ostwald coefficient.

In the third step, determine the amount of oxygen and nitrogen evolved from the fuel. Assuming that the precipitated gas and the dissolved gas are in equilibrium, the newly added equilibrium volume V _E has the following relationship with the mass and partial pressure of the precipitated gas from the ideal gas equation.

Substituting formulas (3) and (4) into formulas (1) and (2), and according to the equilibrium volume V _E in the ideal gas state equation are equal, the amount of oxygen and nitrogen evolved can be obtained.

The fourth step is to take the gas phase space of the fuel tank as the research object to determine the discharge volume of oxygen and nitrogen in the gas phase space and the partial pressure of each gas component under the new equilibrium. Assuming that the gas precipitated in the fuel is fully mixed with the original gas in the gas phase space, the mixed gas will be discharged according to their respective molar ratios, and the discharge volume is determined by the total pressure _Pt2 at the last moment and the pressure of the fuel tank vent. The equilibrium existing in the gas phase space is,

O _U,mix ＝O _U1 +O _F,OUT ＝O _U2 +O _U,OUT (5)

N _U,mix ＝N _U1 +N _F,OUT ＝N _U2 +N _U,OUT (6)

In the formula, 1 represents the original state of the gas phase space, and 2 represents the state after the gas is exhausted. The amounts of oxygen and nitrogen O _U1 and N _U1 and O _U2 and N _U2 are determined by their partial pressures in the gaseous space.

The total pressure of the gas phase space after mixing can be calculated by formula (7). Oxygen and nitrogen are discharged in proportion to the respective mole fractions X _O,mix and X _N,mix , and the mole fraction ratio and partial pressure ratio are the same.

At the end of each time step, the partial pressures of oxygen and nitrogen under the new balance can be obtained according to the total pressure of the fuel tank gas phase space P _t2 and the fuel vapor pressure P _v2 at this time, as follows:

p _OU2 ＝p _NU2 (X _O.mix /X _N.mix ) (9)

In the fifth step, the dissolved amounts N _F2 and _OF2 of nitrogen and oxygen in the fuel oil at the last moment calculated in the second step, and the partial pressures of each gas in the gas phase space under the new equilibrium obtained in the fourth step are taken as the following A parameter at the initial moment in a △t time period is used for the next round of inert calculation.

In the existing inertization experiments or analysis models, most of the situations considered are non-combat environments, and the basic flow of the existing inertization analysis is shown in the left diagram of Figure 2. When a military aircraft is engaged in combat, it is likely to be hit by threats such as projectiles or missile fragments. When the threat penetrates the fuel tank and enters the internal space, it often carries heat and outside air into the oil-gas space. Whether this situation will affect the oxygen concentration, so that the components in the gas phase space are in the flammable range, is worth analyzing. The present invention considers the change of velocity and temperature after the threat breaks through the tank wall, the air brought in due to the entry of the threat, the heat exchange between the threat and the surrounding environment, the change of the concentration of the oil-gas mixture in the gas phase space, etc., to form a A fuel inerting analysis method that considers threat impact and modifies existing inerting models. Wang Mingming and others proposed a method to establish a fuel tank inerting model in the article "Comparative Analysis of Aircraft Fuel Tank Flushing and Washing Inerting Technology" published in the "Journal of Nanjing University of Aeronautics and Astronautics" on 2010-10-15. The theoretical model of fuel washing is established, the process of fuel washing is analyzed, and the relationship of oxygen volume concentration in the gas phase space in the fuel tank with time is obtained through the model, but this model is only suitable for analyzing fuel washing when there is no projectile impact, and does not consider The impact of projectile impact on the oxygen concentration in the gas phase space in the fuel tank, and in the battlefield environment, military aircraft are likely to be hit by projectiles. The analysis method provided by the invention considers the impact of projectile impact on the inerting of aircraft fuel tank, and finally provides the relationship of oxygen concentration in the gas phase space of aircraft fuel tank with time when the projectile impacts.

Contents of the invention

In order to overcome the limitation that the existing inerting model does not consider the impact of the threat on the fuel tank, the present invention proposes a method for analyzing the impact of projectile impact on the inerting of the aircraft fuel tank.

Concrete steps of the present invention are:

1. A method of analyzing the impact of projectile impact on the inerting of aircraft fuel tank, characterized in that, the specific process is:

Step 1: Calculate the remaining velocity of the projectile hitting the tank wall based on the initial conditions.

Assuming that the blunt projectile is incident perpendicular to the target plate, the remaining velocity V _r of the projectile is determined by applying the JTCG/ME residual velocity equation as,

In the formula, V is the impact velocity of the projectile, the unit is m/s; V ₅₀ is the projectile limit of the projectile, the unit is m/s; t is the thickness of the target, the unit is m; ρ is the target material density, the unit is kg/s m ³ ; A _p is the exposed area of the projectile, in m ² ; m is the mass of the projectile, in kg; θ is the incident angle of the projectile, in °.

The ballistic limit refers to the impact velocity when the projectile just penetrates the target, that is, the remaining velocity after the projectile completely passes through the fuel tank wall is 0m/s; that is, the incident velocity when the projectile penetrates the target penetration probability is 50% . The ballistic limit can be obtained by the following formula:

In the formula, L is the perimeter of the exposed area in m, and s is the shear resistance of the target target material in Pa.

Step 2: Analyze the energy change after the projectile penetrates the tank wall.

Neglecting the heat loss of the projectile in the process of breaking through the tank wall, the heat energy converted from plastic work is stored as internal energy, that is,

Among them, β is the heat transfer coefficient of plastic work, Q is the internal energy of the projectile, and △E is the heat energy converted by the projectile due to plastic work.

In order to maximize the impact of the projectile penetration on the gas components in the gas phase space of the fuel tank, it is assumed that the heat converted during the projectile penetration of the fuel tank wall is all transferred to the projectile. Since the thermal conductivity coefficient of the projectile material is high, the interior of the projectile is ignored The temperature gradient of the projectile is assumed to be the same everywhere.

Step 3: Analyze the heat transfer during the movement of the projectile in the fuel tank and calculate the increased fuel vapor volume due to the evaporation of fuel droplets during the heat transfer process.

When the projectile passes through the gas phase space of the fuel tank, the energy flux q″ of heat transfer is determined by formula (13):

q″=h(TT _∞ ) (13)

In the formula, T is the surface temperature of the projectile; T _∞ is the temperature of the airflow generated by the movement of the projectile; h is the heat transfer coefficient of convective heat exchange; the unit of the heat transfer energy flux q″ is W/m ² .

Under the condition of convective heat exchange, the heat transfer coefficient h _conv of the projectile is determined by the cylinder heat transfer coefficient formula (14):

where k is the thermal conductivity of air or fuel, Pr is the Prandtl number, and Re _D is the Reynolds number based on the length D.

Since the temperature of the projectile is the same everywhere, the temperature change of the projectile during its movement in the fuel tank is determined by formula (15):

In the formula, c is the specific heat capacity of the projectile material; A _f is the contact area between the projectile and the surrounding environment, is the change in temperature with time.

It is assumed that the heat transferred by the projectile during the movement is all used to evaporate the fuel droplets suspended in the gas phase space, and the fuel vapor is formed to gather at the tail of the fragment and mix with the incoming air. The mass evaporation rate m" _drop of liquid fuel is:

In the formula, C _f is the specific heat capacity of the fuel, T _b is the boiling point of the fuel, T is the initial temperature of the fuel, h _q is the heat of vaporization of the fuel.

Step 4: Calculate the amount of air entrained by the projectile as it penetrates the tank.

For the projectile, the air volume V _air brought into the fuel tank is:

V _air ＝A _p ·s (17)

In the formula, A _p is the exposed area of the projectile, the unit is m ² ; s is the movement distance of the projectile, the unit is m.

Step 5: Correct the existing inert model.

The air quality brought in by the projectile is A _air , then the new oxygen amount O′ _U,mix in the gas phase space in formula (7) needs to add the amount of oxygen in the air brought in, so:

Determine the new nitrogen amount O' _{U in the gas phase space by formula (19), the amount of nitrogen in the air that is brought into the mix} :

In the formula, M _air is the molar mass of air, M _N and M _O are the molar masses of nitrogen and oxygen, respectively. Considering that the projectile brings in a part of the air when the fuel tank is fed into the air, the formulas (5) and (6) become respectively,

O _U,mix ＝O _U1 +O _F,OUT +O _air ＝O _U2 +O _U,OUT (20)

N _U,mix ＝N _U1 +N _F,OUT +N _air ＝N _U2 +N _U,OUT (21)

In the case of projectile impact, the partial pressure of the fuel vapor increase due to the heat transfer of the projectile in the gas phase space is p _vb , then the new partial pressure of fuel vapor in formula (7) is

p′ _v1 ＝p _v1 +p _vb (22)

Then formula (7) becomes

Assuming that due to the fuel vapor formed by the impact of the projectile and the air brought in, the components in the original mixed equilibrium state are fully mixed again, so the discharge ratio of the mixed gas is the molar ratio in the new equilibrium state.

The invention is an amendment to the existing aircraft fuel tank inerting model. First, according to the initial conditions, calculate the motion state parameters after the projectile penetrates the fuel tank wall, such as the remaining velocity of the projectile, etc., then analyze the energy change after the projectile penetrates the fuel tank wall, and analyze the heat transfer of the projectile during the movement in the fuel tank And calculate the amount of fuel vapor increased by the evaporation of the resulting fuel droplets, and calculate the amount of air in the external environment brought in when the projectile penetrates the fuel tank wall and enters the gas phase space of the fuel tank. Finally, according to the above analysis, the existing inert model to be corrected. The invention can be used to analyze the impact of projectile parameters and environment parameter changes on the gas concentration in the gas phase space in the combat environment, and then determine whether the fuel tank is combustible. The present invention provides an example of a projectile hitting a fuel tank for a single time to verify the correctness of the analysis method. As shown in the final result, when the projectile penetrates the wall thickness of the fuel tank and passes through the interior of the fuel tank, the oxygen and fuel vapor in the gas phase space The concentration change is shown in Figure 4 and Figure 5, and the oil-gas concentration ratio change is shown in Figure 6. Since the projectile enters and brings in a part of the air, the oxygen concentration gradually increases, and with the evaporation of the fuel droplets suspended in the gas phase space , the amount of fuel vapor generated gradually increases, and the oxygen concentration gradually decreases, but the amount of fuel vapor generated by fuel droplets is relatively small compared to the amount of air entering, so the concentration of fuel vapor will gradually decrease, so the projectile can be determined according to the flammable concentration range of fuel Whether the oil/gas concentration in the fuel tank is in a flammable state under strike conditions will further provide a reference for the survivability design of the fuel tank.

Description of drawings

Accompanying drawing 1 is the schematic diagram of fuel washing process in unit time step;

Accompanying drawing 2 is the existing inert analysis model and the inert analysis model considering projectile impact. In the figure: the left side is the existing fuel washing process, and the right side is the flow chart of model correction when considering projectile impact;

Accompanying drawing 3 is a schematic diagram of fragments penetrating the fuel tank and entering the air; in the figure: 1. gas phase space; 2. projectile impact; 3. fuel oil;

Accompanying drawing 4 is the change curve of oxygen concentration in gaseous space, among the figure: solid line represents the change curve of gaseous space oxygen concentration when projectile hits, and dotted line represents the change curve of gaseous space oxygen concentration when no projectile hits;

Accompanying drawing 5 is the change curve of the fuel vapor concentration in the gas phase space, in the figure: the dotted line represents the change curve of the fuel vapor concentration in the gas phase space when the projectile hits, and the dotted line represents the change curve of the fuel vapor concentration in the gas phase space when there is no projectile impact;

Accompanying drawing 6 is the change curve of oil/gas concentration ratio in gas phase space, among the figure: the dotted line represents the change curve of oil/gas concentration ratio in gas phase space space when the projectile hits, and the dotted line represents the change curve of oil/gas concentration ratio in gas phase space when there is no projectile impact ;

Accompanying drawing 7 is the flowchart of the present invention.

Detailed ways

This embodiment takes the impact of a single impact of a projectile on the gas concentration in a fuel tank as an example to illustrate the analysis method for the impact of a projectile impact on the inerting of an aircraft fuel tank proposed by the present invention.

Step 1: Based on the initial conditions, calculate the remaining velocity of the projectile hitting the tank wall.

In the present embodiment, the projectile is the ordinary projectile of the U.S. 12.7mm caliber machine gun, and the parameters of the projectile are as shown in Table 1:

Table 1 Specifications and parameters of 12.7mm machine gun ammunition

type caliber full length Full bomb mass bullet diameter warhead length warhead mass Bullet muzzle velocity Ordinary bullet 12.7mm 137.8mm 116g 12.98mm 57.18mm 46.01g 858m/s

Assuming that the velocity of the projectile is attenuated by 200m/s when it encounters the aircraft fuel tank, the flight speed of the aircraft is 250m/s, the projectile and the aircraft fly opposite and collide head-on, that is, the incident angle θ of the projectile is 0°, and the relative velocity of the projectile when it hits the fuel tank It is 900m/s. The aircraft fuel tank is an aluminum fuel tank with a size of 1×1×0.5m and a wall thickness of 3mm. The shear resistance of aluminum is 69 (MP), and the ballistic limit is determined by formula (11):

In formula (11), V is the impact velocity of the projectile (m/s), t is the thickness of the target (tank wall) (m), θ is the incident angle of the projectile (°), and L is the perimeter of the exposed area (m ), s is the shear resistance (Pa) of the target target plate material.

Among them, the perimeter L of the exposed area of the projectile is determined by the formula (24):

In formula (24), d is the diameter (m) of the projectile.

Applying the JTCG/ME residual velocity equation, that is, formula (10), the residual velocity V _r (m/s) of the projectile can be determined as,

In the formula, V is the impact velocity of the projectile (m/s), V ₅₀ is the projectile limit of the projectile (m/s), t is the thickness (m) of the target (oil tank wall), and ρ is the target material density (kg/m ³ ), A _p is the exposed area of the projectile (m ² ), m is the mass of the projectile (kg), and θ is the incident angle of the projectile (°).

The exposed area A _p is determined by formula (25):

In summary, V _r =886.50m/s is obtained.

Step 2: Analyze the energy change after the projectile penetrates the tank wall.

When the projectile penetrates the wall of the fuel tank, the projectile will lose speed, and the wall of the fuel tank will undergo plastic deformation, and the temperature at the perforation of the projectile and the wall of the fuel tank will change due to the effect of shear stress during the penetration process. Neglecting the heat loss of the penetrator during the process of breaking through the tank wall, the heat energy converted from plastic work is stored as internal energy. Use the formula (12) to calculate the internal energy of the projectile:

Among them, β is the plastic work heat transfer coefficient. The β value ranges from 0.5 to 0.9 for 2024 aluminum at a strain rate of 3000s ^-1 ; therefore, β is taken as 0.9 in the calculation to calculate the maximum internal energy that the projectile can achieve.

In this embodiment, Q=798.50J.

Step 3: Analyze the heat transfer of the projectile during its movement in the fuel tank and calculate the increased vapor volume of the fuel 3 due to the evaporation of the resulting fuel droplets.

Since the temperature of the projectile is the same everywhere, the temperature change of the projectile during its movement in the fuel tank is determined by the following formula:

In the formula, the specific heat capacity of the projectile material c=439. The contact area A _f of the projectile and the surrounding environment is calculated by formula (26):

A _f ＝π×0.01298×0.05718+A _p ＝2.464×10 ^-3 ( ^m2 ) (26)

The impact of the projectile will cause the liquid fuel 3 in the fuel tank to slosh, and small fuel droplets will appear in the gas phase space 1. When the high-temperature projectile moves in the fuel tank, the fuel droplets it encounters will evaporate. It is assumed that the heat transferred by the projectile during its movement is all used to evaporate the fuel droplets suspended in the gas phase space, and the fuel vapor is formed to gather at the tail of the fragment and mix with the incoming air. The mass evaporation rate of liquid fuel oil is:

In the formula, the specific heat capacity of fuel oil C _f =3.01×T+729, the boiling point of fuel oil T _b =-3899/(log(P _t )-21.536859), the initial temperature of fuel oil T=278.4, which is the heat of vaporization of fuel oil h _q = 291000.

Step 4: Calculate the amount of air entrained by the projectile as it penetrates the tank.

For a cylindrical projectile, the air volume V _air brought into the fuel tank is determined by formula (17):

V _air ＝A _p ·s (17)

In the formula, the exposed area A _p of the projectile = 1.3232×10 ^-4 m ² ; s is the movement distance of the projectile, and the unit is m. The volume of air carried into the fuel tank by the projectile will vary over time.

Step 5: According to the above considerations, modify the existing inert model.

The air quality brought by the projectile into the fuel tank is A _air , which is determined by formula (27):

A _air = V _air × ρ _air (27)

Wherein, ρ _air =1.29kg/m ³ .

In the air brought in, the amount of oxygen O _air is determined by formula (18):

In the air brought in, the amount N _air of nitrogen is determined by formula (19):

In formulas (18) and (19), M _air is the molar mass of air, and M _N and M _O are the molar masses of nitrogen and oxygen, respectively. The amounts of oxygen and nitrogen in gas phase space 1 in the mixed gas are calculated by formulas (20) and (21) respectively:

O _U,mix ＝O _U1 +O _F,OUT +O _air ＝O _U2 +O _U,OUT (20)

N _U,mix ＝N _U1 +N _F,OUT +N _air ＝N _U2 +N _U,OUT (21)

Under projectile strike 2, the partial pressure of the fuel vapor increment evaporated due to the heat transfer of the projectile in the gas phase space is p _vb , and the new partial pressure of fuel vapor p′ _v1 is determined by formula (22):

p′ _v1 ＝p _v1 +p _vb (22)

The total pressure Pt _,mix of the gas phase space after mixing is determined by formula (23):

Assuming that the fuel vapor and the air brought in due to the impact of the projectile 2 are fully mixed with the components in the equilibrium state after mixing, the discharge ratio of the mixed gas is the molar ratio of the gas phase space at this time.

In this embodiment, when the projectile breaks through the wall thickness of the fuel tank and passes through the interior of the fuel tank, the concentration changes of oxygen and fuel vapor in the gas phase space are shown in Figure 4 and Figure 5: because the projectile enters and brings in a part of the air, making The oxygen concentration gradually increases, and with the evaporation of the fuel droplets suspended in the gas phase space, the amount of fuel vapor generated gradually increases, and the oxygen concentration gradually decreases, but the amount of fuel vapor generated by the fuel droplets is relatively small compared to the amount of air entering , so the concentration of fuel vapor will gradually decrease, so the concentration of oxygen and fuel vapor in the gas phase space of the fuel tank increases first and then gradually decreases when the projectile hits, but the concentrations of oxygen and fuel vapor in the gas phase space of the fuel tank are generally higher than those of no Concentration at impact of the projectile.

The change of the oil/gas concentration ratio in the gas phase space is shown in Figure 6: when the projectile hits, the oil/gas concentration ratio in the gas phase space increases first and then gradually decreases, but it is generally greater than the concentration without projectile impact.

Claims (3)

1. a kind of analyze the method that is influenced on Inerting Aircraft Fuel Tanks of projectile impact, which is characterized in that detailed process is：

Step 1：The residual velocity of projectile impact oil tank wall is calculated according to primary condition；

Assuming that blunt nosed bullet is incident perpendicular to target plate, the residual velocity V of bullet is determined using JTCG/ME residual velocity equations_r For,

In formula, V be bullet stroke speed, unit m/s；V₅₀For the bullet limit of bullet, unit m/s；T is the thickness of target Degree, unit m；ρ be target material density, unit kg/m³；A_pFor the exposed area of bullet, unit m²；M is the matter of bullet Amount, unit kg；θ is the incident angle of bullet, and unit is °；

Step 2：Analyze the variation that bullet punctures energy after oil tank wall；

Ignore heat loss of the bullet during oil tank wall is punctured, the thermal energy of plastic work done conversion is stored as the form of interior energy, i.e.,

Wherein, β turns hot coefficient for plastic work done, and Q is the interior energy of bullet, and △ E are the thermal energy that bullet is converted due to plastic work done；

Step 3：Fuel droplets steam during analyzing heat transfer of the bullet in fuel tank in motion process and calculating heat transfer It sends out and increased fuel-steam amount；

During bullet is through fuel tank gas-phase space, the flux of energy q " of heat transfer is determined by formula (13)：

Q "=h (T-T_∞) (13)

In formula, T is bullet surface temperature；T_∞The temperature of air-flow is generated for Projectile Motion；H is the heat transfer coefficient of convective heat exchange； The unit of the flux of energy q " of the heat transfer is W/m²；

Under the conditions of convective heat exchange, bullet heat transfer coefficient h_convIt is determined by cylinder heat transfer coefficient formula (14)：

In formula, k is the thermal conductivity factor of air or fuel oil, and Pr is Prandtl number, Re_DIt is the Reynolds on the basis of length is D Number；

Due to bullet, temperature is identical everywhere, therefore the variation of bullet its temperature in motion process in fuel tank is true by formula (15) It is fixed：

In formula, c is the specific heat capacity of bullet material；A_fFor the contact area of bullet and ambient enviroment,It is the change of temperature at any time Change amount；

If the heat that bullet transfers during the motion is completely used for the fuel droplets to suspend in evaporation gas-phase space, fuel oil is formed Steam is gathered in fragmentation afterbody and is mixed with the air entered；The mass rate vaporization m " of liquid fuel_dropFor：

In formula, C_fFor the specific heat capacity of fuel oil, T_bFor the boiling point of fuel oil, T is the initial temperature of fuel oil, h_qFor the heat of evaporation of fuel oil；

Step 4：Calculate the amount that bullet penetrates the air brought into during fuel tank；

For bullet, the volume of air V in fuel tank is brought into_airFor：

V_air=A_p·s (17)

In formula, A_pFor the exposed area of bullet, unit m²；S be bullet move distance, unit m；

Step 5：Existing inerting model is modified；

The air quality that bullet is brought into is A_air, amount of oxygen O ' new in the stagnation pressure of gas-phase space after mixing_U,mixIt needs to add and bring into Air in oxygen amount, therefore：

The new nitrogen amount O ' of gas-phase space is determined by formula (19)_U,mixIn nitrogen in the air brought into amount：

In formula, M_airFor the molal weight of air, M_N、M_OThe respectively molal weight of nitrogen and oxygen；Consider bullet during fuel tank air inlet Ball brings portion of air into, nitrogen amount in gas-phase space after amount of oxygen OU, mix and gas mixing in gas-phase space after gas mixing NU, mix are respectively：

O_U,mix=O_U1+O_F,OUT+O_air=O_U2+O_U,OUT (20)

N_U,mix=N_U1+N_F,OUT+N_air=N_U2+N_U,OUT (21)

In projectile strike, because the fuel-steam increment that the heat transfer of bullet is evaporated in the partial pressure of gas-phase space is p_vb, then Fuel-steam new in the stagnation pressure of gas-phase space partial pressure is after mixing

p′_v1=p_v1+p_vb (22)

The stagnation pressure of gas-phase space is after then mixing

Assuming that each component of the fuel-steam formed due to projectile strike and the air brought into and equilibrium state after original mix Be sufficiently mixed again, thus the discharge ratio of mixed gas be new equilibrium state when molar ratio.

2. the method that analysis projectile impact influences Inerting Aircraft Fuel Tanks as described in claim 1, which is characterized in that step 1 Described in the bullet limit pass through formula (11) obtain：

In formula, L is the perimeter of exposed area, and unit m, s are the shearing resistance of target plate material, unit Pa.

3. the method that analysis projectile impact influences Inerting Aircraft Fuel Tanks as described in claim 1, which is characterized in that step 2 In the variation of energy after analyzing bullet breakdown oil tank wall, in order to penetrate bullet to each gas component in fuel tank gas-phase space It influences to maximize, if the heat converted during bullet breakdown oil tank wall has all passed to bullet, due to leading for bullet material Hot function is higher, therefore ignores the temperature gradient inside bullet, if temperature is identical everywhere for bullet.