High-altitude balloon appearance and trajectory prediction system and method based on multidisciplinary fusion

Abstract

The invention relates to a multidisciplinary fusion-based high-altitude balloon appearance and trajectory prediction system and method, and the method comprises the steps: building a thermodynamic inflation analysis module, a computational fluid mechanics module and a flight dynamics theory analysis module, and carrying out the coupling solving analysis through a multidisciplinary module; the dynamic change of the thermodynamic shape, the aerodynamic characteristic and the motion characteristic of the balloon in the high-altitude motion process can be rapidly obtained, the coupling influence of the flight trajectory height and the shape in the working process of the high-altitude balloon can be truly reflected, the accuracy is good, and the efficiency is higher.

Description

Technical Field

[0001] The invention relates to a system and method for predicting the shape and trajectory of a high-altitude balloon based on multidisciplinary integration, and belongs to the technical field of design and analysis of high-altitude balloons. Background Art

[0002] In recent years, the research on stratospheric aerostats has attracted the attention of various countries, and many research institutions have carried out research on related technologies and applications. Stratospheric aerostats are located above aircraft and below spacecraft, and there are many types, such as high-altitude balloons. High-altitude balloons have many advantages such as long air time, low operating costs, and good safety. They have broad application prospects in the fields of earth observation, relay communications, early warning monitoring, etc. The working altitude of high-altitude balloons is an important guarantee for their successful mission execution. Therefore, establishing a rapid prediction method for the flight trajectory of high-altitude balloons is of great significance to their structural design and performance optimization.

[0003] At present, some studies simplify the balloon into a particle system based on the flight dynamics method, establish the particle dynamics equation, and calculate the change of its height with meteorological conditions and inflation pressure; some studies use commercial computing software to study the thermodynamic changes of balloon temperature, volume, pressure, etc. in different environments. However, the inflation of a balloon at high altitude is not a simple dynamic or thermodynamic process. On the one hand, it will experience a complex atmospheric environment, and parameters such as atmospheric pressure and temperature will change greatly with altitude; on the other hand, it is in a complex thermal environment and is affected by external radiation and atmospheric convection. Both factors may cause drastic changes in the shape of the balloon, which in turn causes changes in its aerodynamic characteristics. Therefore, when predicting the trajectory, it is necessary to consider the coupled changes of the balloon shape and aerodynamic characteristics and the mutual influence between the two.

[0004] In summary, how to couple the multidisciplinary analysis of the working process of the high-altitude balloon to quickly and accurately obtain the changes in the shape and trajectory of the high-altitude balloon during the inflation process, provide a reference for the design of the high-altitude balloon, and is very important for the subsequent research and expansion of the stratospheric aerostat. Summary of the invention

[0005] In response to the above problems, the application discloses a method for determining the shape and trajectory of a high-altitude balloon based on multidisciplinary integration. It adopts a multidisciplinary coupling analysis method, based on thermodynamic analysis, computational fluid dynamics and flight mechanics theory, to establish thermodynamic deformation, computational fluid and flight mechanics modules respectively. By transferring thermodynamic, fluid dynamics and flight mechanics parameters between modules, it is possible to quickly calculate the dynamic changes of the shape and altitude of a high-altitude balloon from the beginning of inflation to the fullness, providing a reference for the design and analysis of high-altitude balloons.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A high-altitude balloon shape and trajectory prediction system based on multidisciplinary integration, including:

[0008] Thermodynamic inflation analysis module takes the real-time altitude of the balloon as input and outputs the buoyancy, inflation volume and shape change of the balloon according to the gas state equation and energy conservation equation;

[0009] The computational fluid dynamics module takes the balloon shape and real-time altitude as input, and sequentially establishes the geometric model, the flow field grid numerical model, and the flow field numerical model to obtain the aerodynamic force and aerodynamic characteristic changes of the balloon;

[0010] The flight dynamics module uses the aerodynamic force and buoyancy of the balloon as input, performs dynamic analysis on the balloon system, establishes the particle dynamics motion equation of the balloon, and obtains the motion characteristic changes of the balloon speed and real-time ballistic height;

[0011] By coupling each module to transfer parameters and perform calculation analysis, the dynamic changes of the shape and height of the high-altitude balloon from the beginning of inflation to fullness are obtained.

[0012] The present invention also discloses a method for predicting the shape and trajectory of a high-altitude balloon based on multidisciplinary integration, comprising the following steps:

[0013] Step 1, determine the inflation environment of the high-altitude balloon, and predict the real-time buoyancy, volume and shape changes of the high-altitude balloon during the high-altitude inflation and floating process after being filled according to the real-time altitude and speed motion parameters of the balloon, based on the function of the thermodynamic inflation analysis module, and according to the gas state equation and energy conservation equation;

[0014] Step 2: According to the volume and shape of the balloon and based on the function of the computational fluid dynamics module, a geometric model, a grid model and a flow field calculation model of the balloon in the flow field are established to calculate the changes in the aerodynamic characteristics of the balloon;

[0015] Step 3: Perform dynamic analysis on the balloon system. Based on the flight dynamics module function, the particle dynamics motion equation of the balloon is established according to the aerodynamic force and buoyancy of the balloon, and the speed and height change of the balloon are obtained;

[0016] Step 4: Execute steps 1-3 at each time step, obtain all the information at that moment, iterate to the next time step, repeat steps 1-3, and then obtain the transient changes of balloon thermodynamics, aerodynamic characteristics and flight dynamics parameters.

[0017] Beneficial Effects

[0018] The present invention adopts a multidisciplinary and modular design method to couple the thermodynamic analysis, computational fluid dynamics analysis and flight dynamics analysis of high-altitude balloons, reflecting the essential working characteristics that changes in shape cause changes in aerodynamic force and then change ballistic characteristics, and can quickly and accurately predict changes in the shape and trajectory of high-altitude balloons. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Flow chart of the high-altitude balloon shape and trajectory prediction system based on multidisciplinary integration designed for the present invention;

[0020] Figure 2 This is the curve of the change of the volume of a high-altitude balloon during its descent after being inflated;

[0021] Figure 3 This is the curve of the temperature change of the gas inside the balloon during the descent of the high-altitude balloon;

[0022] Figure 4 This is the appearance of a high-altitude balloon when it is filled;

[0023] Figure 5 Details of the grid model for high-altitude balloon and parachute flow field simulation;

[0024] Figure 6 This is the pressure distribution diagram of the flow field around the high-altitude balloon;

[0025] Figure 7 This is the velocity distribution diagram of the flow field around a high-altitude balloon;

[0026] Figure 8 This is the force diagram of the high-altitude balloon during the inflation process;

[0027] Fig. 9 It is the height change curve of the high-altitude balloon during its descent after being inflated;

[0028] Fig.10 This is the velocity change curve of a high-altitude balloon during its descent after being inflated. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the available embodiment library of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] The present invention discloses a high-altitude balloon shape and trajectory prediction system based on multidisciplinary integration, such as Figure 1As shown in the figure, a modular design method is adopted to establish a thermodynamic inflation analysis module, a computational fluid dynamics module and a flight dynamics module.

[0032] The thermodynamic inflation analysis module calculates the balloon's inflation volume and its shape changes based on the gas state equation and the energy conservation equation. The computational fluid dynamics module sequentially establishes a geometric model, a flow field grid numerical model, and a flow field numerical model based on the shape of the high-altitude balloon to obtain the balloon's aerodynamic characteristics and aerodynamic changes. The flight dynamics module establishes the balloon's particle dynamics motion equation based on the dynamics analysis of the balloon system to obtain the changes in the balloon's speed and altitude motion characteristics. By coupling the modules, parameter transfer and computational analysis are performed to ultimately obtain the dynamic changes in the shape and altitude of the high-altitude balloon from the beginning of inflation to fullness.

[0033] Thermodynamic inflation analysis module: takes the real-time height h of the balloon as input, and outputs the balloon's buoyancy F and inflation volume V according to the gas state equation and energy conservation equation q and changes in appearance.

[0034] Output inflation volume V q Based on the mass of the gas filled m q , obtain the current volume V of the balloon through the gas state equation q , expressed as:

[0035]

[0036] Where M q is the molar mass of the gas filled, R is the gas constant; P q 、T q are the pressure and temperature of the filled gas, pressure P q The temperature T is obtained from the height of the target balloon. q It is derived from the heat balance equation.

[0037] To determine the filling gas temperature T q The balloon system is divided into two parts: the balloon internal gas and the balloon skin. The thermodynamic equilibrium is established according to the energy conservation equation. The heat balance equations of the balloon internal gas and the balloon skin are combined to obtain the filling gas temperature T q .

[0038] For the gas inside the balloon: the gas inside the balloon is considered to be completely transparent, so the gas does not absorb thermal radiation from the outside and only transfers heat with the balloon membrane.

[0039] The heat transfer between the balloon's internal gas and the skin is in the form of natural convection in the spherical internal space, and the heat transfer amount Q int for

[0040] Qint =h int (T f -T q )S

[0041] Where, T f is the skin temperature, T q is the gas temperature; S is the balloon surface area; h int is the natural surface heat transfer coefficient between the gas inside the balloon and the skin.

[0042] According to the first law of thermodynamics, the change in internal energy of the gas is equal to the heat exchange between the gas and the outside world minus the work done to the outside world. Therefore, the heat balance equation inside the balloon is:

[0043]

[0044] The above equation is the heat balance equation inside the balloon. q is the mass of the gas, C q is the specific heat capacity of the gas, M a is the relative molecular mass of air, g is the acceleration due to gravity, and is taken as 9.8 N·m 2 / kg 2 , M q is the relative molecular mass of the gas, is the vertical velocity of the balloon.

[0045] For balloon skin: The main heat exchange of the skin includes natural convection heat exchange Q1 between the inner surface of the skin and the gas inside the balloon, and convection heat exchange between the outer surface of the skin and the ambient atmosphere through the ambient heat radiation absorbed by the skin.

[0046] The natural convection heat transfer Q1 between the inner surface of the skin and the gas inside the balloon can be expressed as:

[0047] Q1=h int (T f -T q )S

[0048] The convective heat transfer Q2 between the outer surface of the skin and the ambient atmosphere can be expressed as:

[0049] Q2=h ext (T a -T f )S

[0050] In the formula, h ext is the forced surface heat transfer coefficient between the skin and the air; T a is the atmospheric temperature, which can be obtained from the altitude of the target balloon.

[0051] External heat radiation Q3 can be expressed as

[0052] Q3=αf (Q down +Q up )A

[0053] In the formula, α f is the absorption rate of the skin; A is the windward area of ​​the balloon; Q down is the heat from solar radiation and scattering from the upper atmosphere, Q up The heat is the scattering of the lower atmosphere and the thermal radiation of the surface.

[0054] The balloon surface radiates heat outwards Q4

[0055]

[0056] In the formula, ε f is the emissivity of the skin in the infrared band, and σ is the Stefan-Boltzmann constant.

[0057] Therefore, the thermal balance equation of the skin is:

[0058]

[0059] Combine the heat balance equations of the balloon's internal gas and the balloon's skin to find the filling gas temperature T q .

[0060] The output buoyancy F is: The buoyancy F of the balloon is output according to the current volume V of the balloon. The buoyancy acts at the center of the balloon and is vertically upward according to the following formula:

[0061] F=ρgV q

[0062] Where g = 9.8 m / s 2 is the acceleration due to gravity, and ρ is the density of the balloon, which is determined in real time during the inflation process by thermodynamic calculations.

[0063] The output balloon shape changes as follows: According to the balloon filled shape characteristic diameter D0 and filled volume V0, the balloon characteristic diameter change is scaled according to the principle of geometric similarity and can be expressed as:

[0064]

[0065] To determine the filling gas temperature T q The balloon system is divided into two parts: the balloon's internal gas and the balloon's skin, and thermodynamic equilibrium is established for each part based on the energy conservation equation.

[0066] Computational fluid dynamics module: Taking the shape and real-time altitude of the balloon as input, the geometric model, flow field grid numerical model, and flow field numerical model are established in sequence to obtain the aerodynamic characteristics and aerodynamic changes of the balloon.

[0067] According to the real-time volume and shape of the balloon, the geometric model of the high-altitude balloon is established through 3D CAD modeling software.

[0068] A flow field grid discrete model is established based on the geometric model. In this embodiment, the flow field domain is 8c*8c*12c, where c is the characteristic length of the high-altitude balloon. The flow field domain is divided into tetrahedral grids, and the flow field near the high-altitude balloon is encrypted.

[0069] The flow field calculation model is established based on the flow field grid discrete model, and the flow field control equation is:

[0070]

[0071] Where ρ is the density of the fluid, t is the time, v is the velocity vector of the fluid, p is the pressure of the fluid, τ is the stress tensor, and f is the volume force on the fluid.

[0072] The flow field density ρ is obtained according to the ideal gas state equation as follows:

[0073]

[0074] Where P is the ambient flow field pressure, M is the molar mass of the ambient atmosphere, and T is the ambient gas temperature.

[0075] The velocity and pressure distribution of the flow field can be obtained based on the flow field calculation. According to the change of pressure distribution on the balloon surface, the change of aerodynamic characteristics of the balloon can be obtained by automatic integration through the flow field calculation software: the aerodynamic characteristics can be obtained by integrating the pressure difference coefficient Cp on the balloon surface, and Cp is automatically output by the flow field calculation module.

[0076] Flight dynamics module: Take the aerodynamic force and buoyancy of the balloon as input, perform dynamic analysis on the balloon system, establish the particle dynamics motion equation of the balloon, and obtain the motion characteristic changes of the balloon speed and real-time altitude.

[0077] After the system is launched, under the action of the parachute, the speed direction can be changed to vertically downward in a short time, so the present invention only considers the movement in the vertical direction and ignores the influence of horizontal wind. The balloon model uses a natural high-altitude balloon without exhaust.

[0078] When the system is inflated and falling, the speed of the relative air movement is v. The force analysis of the balloon shows that the balloon is mainly subject to the vertical upward buoyancy, the downward gravity, and the aerodynamic force opposite to the direction of movement.

[0079] The buoyancy F of the balloon is determined in real time during the inflation process by thermodynamic calculations.

[0080] The aerodynamic drags on the balloon and the parachute are F dq 、F ds, the general calculation formula is as follows:

[0081]

[0082] Where v is the relative air velocity, C d is the drag coefficient, S is the drag area, Characterize the direction of the drag. Take the drag coefficient of the balloon, C dq =0.8, the drag coefficient of the parachute C ds =0.75.

[0083]

[0084] Where D is the vertical cross-sectional radius of the balloon.

[0085] In summary, the core dynamic equation obtained from Newton's second law is:

[0086]

[0087] Among them, M q is the mass of the balloon, M s is the mass of the parachute, M1 and M2 are the equivalent mass of the parachute of the balloon, that is, the sum of the additional mass and the mass of the object. The velocity variation characteristics of the balloon can be obtained according to the dynamic equation.

[0088] For a balloon, the additional mass formula is as follows, where C m is the additional mass coefficient, which takes a value of 0.5:

[0089] M add,q =C m ρV q

[0090] For a parachute, the additional mass formula is as follows, where R t , C A , C t are the parachute projection radius, drag area and tangential aerodynamic coefficient respectively, and C t =0.5:

[0091]

[0092] The height of the balloon system can be calculated from the velocity, and the equation is:

[0093] The aerodynamic force is determined according to the real-time speed and aerodynamic characteristics, and the equation is: Where C is the aerodynamic characteristic, which is obtained by the computational fluid dynamics module.

[0094] The modules of each discipline are coupled to perform computational analysis. Figure 1As shown, the thermodynamic inflation module provides the computational fluid dynamics module with the real-time volume and shape changes of the balloon, and provides the flight dynamics module with the real-time situation of the buoyancy of the balloon; the computational fluid dynamics module provides the flight dynamics module with the changes of the aerodynamic characteristics of the balloon; and the flight dynamics module provides the thermodynamic inflation module and the computational fluid dynamics module with the real-time height changes of the balloon.

[0095] Example 2

[0096] The present invention also discloses a method for predicting the shape and trajectory of a high-altitude balloon based on multidisciplinary integration. The following takes the deceleration and inflation process of a high-altitude balloon near 55 km of the earth as an example. Figures 2 to 10 , specifically describe the implementation steps of the present invention:

[0097] Step 1, determine the inflation environment of the high-altitude balloon, and based on the real-time altitude and real-time velocity motion parameters of the balloon (the initial altitude and initial velocity of the balloon are calculated and input for the first time), predict the real-time volume and shape changes of the high-altitude balloon during the high-altitude inflation and floating process after being filled by the gas state equation and the energy conservation equation.

[0098] In this embodiment, the working altitude of the high-altitude balloon is 50 to 65 km near the earth's atmosphere, and the ideal floating altitude is 55 km. The balloon is inflated after the missile-borne entry device is decelerated and suspended near the working altitude.

[0099] The inflated volume of the balloon and its shape change are calculated based on the balloon's initial volume, inflation pressure, ambient pressure, gas type, gas mass, etc., according to the gas state equation and energy conservation equation.

[0100] In this embodiment, the diameter of the high-altitude balloon is 5m and the inflated volume is 65m 3 The inflation time is no more than 200s; the inflation gas is helium, the total helium mass is 12kg, the volume is 60L, and the inflation pressure is 50MPa.

[0101] The balloon inflation process is a variable mass expansion process of the controlled volume inside the balloon. The corresponding atmospheric pressure P is obtained from the height h of the target balloon. The calculation formula is:

[0102] P = 4.355 × 10 25 h -5.037

[0103] For example, at an altitude of 55 km, the atmospheric pressure is 57.78 Pa.

[0104] According to the momentum equation, the mass flow rate of balloon inflation is related to the area of ​​the inflation port and the pressure difference on both sides. The mass flow rate increases with the increase of the inflation port area and the pressure difference. The mass of the gas filled is m q When the current volume V of the balloon is obtained according to the gas state equation q, the calculation formula is:

[0105]

[0106] Where M q is the molar mass of the gas filled, R is the gas constant; P q 、T q are the pressure and temperature of the filled gas, pressure P q The temperature T is obtained from the height of the target balloon. He It is derived from the heat balance equation.

[0107] The shape change of the balloon is as follows: according to the filled shape of the balloon, the characteristic diameter change of the balloon can be expressed as:

[0108]

[0109] To determine the helium filling temperature T He The balloon system is divided into two parts: the helium inside the balloon and the balloon skin, and thermodynamic equilibrium is established for each part according to the energy conservation equation.

[0110] For the helium inside the balloon: the gas inside the balloon is considered to be completely transparent, so the gas does not absorb thermal radiation from the outside and only transfers heat with the balloon membrane.

[0111] The heat exchange between the helium inside the balloon and the skin is in the form of natural convection in the spherical interior space, and the heat transfer amount Q int for

[0112] Q int =h int (T f -T He )S

[0113] Where, T f is the skin temperature, T He is the gas temperature; S is the balloon surface area; h int is the natural surface heat transfer coefficient between the gas inside the balloon and the skin.

[0114] According to the first law of thermodynamics, the change in internal energy of the helium is equal to the heat exchange between the gas and the outside world minus the work done to the outside world. Therefore, the heat balance equation inside the balloon is:

[0115]

[0116] The above equation is the heat balance equation inside the balloon. He is the mass of helium, C He is the specific heat capacity of helium, M a is the relative molecular mass of air, g is the acceleration due to gravity, and is taken as 9.8 N·m2 / kg 2 , M He is the relative molecular mass of helium, is the vertical velocity of the balloon.

[0117] For balloon skin: The main heat exchange of the skin includes natural convection heat exchange Q1 between the inner surface of the skin and the gas inside the balloon, and convection heat exchange between the outer surface of the skin and the ambient atmosphere through the ambient heat radiation absorbed by the skin.

[0118] The natural convection heat transfer Q1 between the inner surface of the skin and the gas inside the balloon can be expressed as:

[0119] Q1=h int (T f -T He )S

[0120] The convective heat transfer Q2 between the outer surface of the skin and the ambient atmosphere can be expressed as:

[0121] Q2=h ext (T a -T f )S

[0122] In the formula, h ext is the forced surface heat transfer coefficient between the skin and the air; T a is the atmospheric temperature, which can be obtained from the height of the target balloon. The formula is as follows:

[0123] T=2.381×10 -12 h 3 -4.474×10 -7 h 2 +0.02514h-164.3

[0124] For example, at an altitude of 55km, the atmospheric temperature is 261.15K.

[0125] External heat radiation Q3 can be expressed as

[0126] Q3=α f (Q down +Q up )A

[0127] In the formula, α f is the absorption rate of the skin; A is the windward area of ​​the balloon; Q down is the heat from solar radiation and scattering from the upper atmosphere, Q up is the heat of the scattering of the lower atmosphere and the thermal radiation of the surface, and the calculation formula is:

[0128] Q down =161+29.49×10 -3H-0.27×10 -5 H 2

[0129] Q up =35.68+26.23×10 -3 H-0.26×10 -5 H 2

[0130] The balloon surface radiates heat outwards Q4

[0131]

[0132] In the formula, ε f is the emissivity of the skin in the infrared band, and σ is the Stefan-Boltzmann constant.

[0133] Therefore, the thermal balance equation of the skin is:

[0134]

[0135] Combine the heat balance equations of the balloon's internal gas and the balloon's skin to find the filling gas temperature T q .

[0136] In this embodiment, the balloon surface is a polymer skin, and its thermodynamic parameters are: ε = 0.9, σ = 5.67 × 10 -8 W / (m 2 ·K 4 ), h int =5W / (m 2 ·K), h ext =9W / (m 2 K), ε f =0.2, C p =5193 J / (kg·K), C f =2300 J / (kg·K);

[0137] Combine the heat balance equations of the balloon's internal gas and the balloon's skin to find the filling gas temperature T He .

[0138] In this embodiment, the volume of the balloon changes during inflation as shown in FIG. Figure 2 As shown in Figure 2, the change of internal gas temperature is as follows: Figure 3 As shown in the figure, it can be seen that the volume of the balloon gradually increases as it is inflated. At 149.7s, the balloon is full and its volume reaches its maximum. After being filled, the volume of the balloon remains unchanged.

[0139] For the helium inside the balloon, since the heat exchange between the helium inside the balloon and the outside world is less than the work done by the balloon expansion at the beginning of inflation, the temperature of the helium inside the balloon gradually decreases, reaching the lowest temperature of 259.6K at 6s. Afterwards, as the skin temperature rises due to the radiation of the external environment, the temperature of the gas inside the balloon turns to rise under the influence of the increasing skin heat exchange, and tends to stabilize after being filled.

[0140] Step 2: According to the real-time shape of the balloon, a geometric model, a grid model and a flow field calculation model of the balloon in the flow field are established to obtain the changes in the aerodynamic characteristics of the balloon.

[0141] According to the real-time volume and shape of the balloon obtained by the thermodynamic inflation analysis module, the geometric model of the high-altitude balloon and its deceleration device (parachute) is established through 3D CAD modeling software. According to literature experiments, the shape of the balloon during inflation is approximately an eccentric ellipsoid. When the balloon is full, the shape is Figure 4 As shown;

[0142] Based on the geometric model of the balloon, a flow field grid discrete model is established in ICEM. The flow field is a cuboid of 8c*8c*12c, where c is the characteristic length of the high-altitude balloon. The flow field is divided into tetrahedral grids, and the grids of the flow field near the high-altitude balloon and the parachute are encrypted. The schematic diagram of the symmetric interface of the obtained grid model is shown in the figure. Figure 5 As shown;

[0143] The flow field calculation model is established based on the flow field grid discrete model. The flow field around the high-altitude balloon can be regarded as an incompressible flow and is solved using the incompressible NS equation. The flow field control equation is:

[0144]

[0145] Where ρ is the density of the fluid, t is the time, v is the velocity vector of the fluid, p is the pressure of the fluid, τ is the stress tensor, and f is the volume force on the fluid.

[0146] The velocity and direction of the flow field are determined by the real-time flight speed of the balloon, and the flow field density is the ambient atmospheric density, which is obtained according to the ideal gas state equation as follows:

[0147]

[0148] Wherein, P, M, and T are the ambient atmospheric pressure, the molar mass of the ambient atmosphere, and the ambient atmospheric temperature, respectively; R is the gas constant, R = 8.314 J / (mol·K).

[0149] The control equations are solved using the second-order discrete format and the SIMPLEC algorithm, and the turbulence model uses the Realizable k-epsilon model. The pressure and velocity distributions of the balloon flow field can be obtained by calculation, as shown in Figure 6 , 7 As shown in the figure, the results show that due to the blocking effect of the balloon and the parachute on the incoming flow, a low-speed stagnation zone is formed on the windward side of the balloon and inside the parachute, the flow field pressure increases, and flow separation occurs when the airflow flows around the balloon, forming a low-pressure wake zone at the trailing edge of the balloon. Due to the pressure difference between the front and rear, the balloon and the parachute both generate aerodynamic resistance. The aerodynamic characteristics and aerodynamic force received by the high-altitude balloon are obtained based on the pressure distribution on the balloon surface.

[0150] Step 3, perform dynamic analysis on the balloon system, establish the particle dynamics motion equation of the balloon based on the aerodynamic force, buoyancy, and gravity acting on the balloon, and obtain the changes in the velocity and altitude motion characteristics of the balloon.

[0151] After the system is launched, under the action of the parachute, the speed direction can be changed to vertically downward in a short time, so the present invention only considers the movement in the vertical direction and ignores the influence of horizontal wind. The balloon model uses a natural high-altitude balloon without exhaust.

[0152] Perform force analysis on the balloon system, such as Figure 8 As shown in the figure, the speed of the system relative to the air during the process of inflating and falling is . The high-altitude balloon is mainly subject to the vertical upward buoyancy F, the downward gravity G, and the aerodynamic force F in the opposite direction of movement v. dq The deceleration parachute mainly receives the aerodynamic force F ds There is a tension F between the two k After the balloon is pulled out, the posture of the balloon and the parachute remains almost unchanged in the air, so the entire system can be regarded as a double-particle system and the particle dynamics equation can be established.

[0153] The buoyancy F of the balloon acts at the center of the balloon and is directed vertically upward according to the following formula:

[0154] F=ρgV

[0155] Where V is the volume of the balloon, g = 9.8 m / s 2 is the acceleration due to gravity, and ρ is the density of the balloon, which is determined in real time during the inflation process by thermodynamic calculations.

[0156] The aerodynamic drags on the balloon and the parachute are F dq 、F ds , the general calculation formula is as follows:

[0157]

[0158] Where v is the relative air velocity, C d is the drag coefficient, S is the drag area, Characterize the direction of the drag. Take the drag coefficient of the balloon, C dq =0.8, the drag coefficient of the parachute Cds =0.75.

[0159]

[0160] Where D is the vertical cross-sectional radius of the balloon.

[0161] In summary, the core dynamic equation can be obtained from Newton's second law:

[0162]

[0163] Where M q is the mass of the balloon, M s is the mass of the parachute, M1 and M2 are the equivalent mass of the parachute of the balloon, that is, the sum of the additional mass and the mass of the object. For the balloon, the additional mass formula is as follows, where C m is the additional mass coefficient, which takes a value of 0.5:

[0164] M add,q =C m ρV

[0165] For a parachute, the additional mass formula is as follows, where R t , C A , C t are the parachute projection radius, drag area and tangential aerodynamic coefficient respectively, and C t =0.5:

[0166]

[0167] The height of the balloon system can be calculated from the velocity, and the equation is:

[0168] The aerodynamic force is determined according to the real-time speed and aerodynamic characteristics, and the equation is: Where C is the aerodynamic characteristic, which is obtained by the computational fluid dynamics module.

[0169] In this embodiment, the height and speed changes of the balloon during descent are respectively Fig. 9 and Fig.10 It can be seen that due to the change in the balloon's inflated shape and the increase in atmospheric density, the aerodynamic force continues to increase, the system decelerates faster, and the altitude change gradually becomes gentler.

[0170] Each step can only obtain the thermodynamic parameters, aerodynamic characteristics and flight dynamics parameters of the balloon at a given moment by running it separately. Steps 1-3 are executed at each time step, and after obtaining all the information at that moment, it is iterated into the next time step, and steps 1-3 are repeated to obtain the transient changes of the balloon's thermodynamic, aerodynamic characteristics and flight dynamics parameters, such as Figure 2 , Figure 3 as well as Fig. 9 , Fig.10 shown.

[0171] The above technical solution designs a method for determining the shape and trajectory of a high-altitude balloon based on multidisciplinary integration. It adopts a multidisciplinary coupling analysis method, and based on thermodynamic analysis, computational fluid dynamics and flight mechanics theory, establishes thermodynamic deformation, computational fluid and flight mechanics modules respectively. By transferring thermodynamic, fluid dynamics and flight mechanics parameters between modules, it can quickly calculate the dynamic changes of the shape and height of the high-altitude balloon from the beginning of inflation to the fullness, and obtain the trajectory and position at different times, which is of great significance to the structural design and performance optimization of the high-altitude balloon.

[0172] The specific implementation modes of the present invention have been described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A high-altitude balloon shape and trajectory prediction system based on multidisciplinary integration, characterized in that: include: Thermodynamic inflation analysis module takes the real-time ballistic height of the balloon as input and outputs the buoyancy, inflation volume and shape change of the balloon according to the gas state equation and energy conservation equation; The computational fluid dynamics module takes the balloon shape and real-time altitude as input, and sequentially establishes the geometric model, the flow field grid numerical model, and the flow field numerical model to obtain the aerodynamic force and aerodynamic characteristic changes of the balloon; The flight dynamics module uses the aerodynamic force and buoyancy of the balloon as input, performs dynamic analysis on the balloon system, establishes the particle dynamics motion equation of the balloon, and obtains the changes in motion characteristics such as the balloon speed and real-time ballistic height; By coupling each module to transfer parameters and perform calculation analysis, the dynamic changes of the shape and height of the high-altitude balloon from the beginning of inflation to fullness are obtained.

2. The system according to claim 1, characterized in that In the thermodynamic charging analysis module, based on the mass m of the charged gas q , output the current volume V of the balloon through the gas state equation q , expressed as: Where M q is the molar mass of the gas filled, R is the gas constant; P q and T q are the pressure and temperature of the filled gas, pressure P q The temperature T is obtained from the height of the target balloon. q It is derived from the heat balance equation; The buoyancy of the output balloon is expressed as: F = ρgV, ρ,V q are the current ambient flow field density and balloon volume respectively, and g is the gravitational acceleration; The shape change of the output balloon is as follows: According to the characteristic diameter D0 of the balloon when it is filled and the filled volume V0, the characteristic diameter change of the balloon is expressed as 3. The system according to claim 2, characterized in that In the thermodynamic charging analysis module, to determine the charging gas temperature T q The balloon system is divided into two parts: the balloon internal gas and the balloon skin. The thermodynamic equilibrium is established according to the energy conservation equation. The heat balance equations of the balloon internal gas and the balloon skin are combined to obtain the filling gas temperature T q .

4. The system according to claim 3, characterized in that The heat balance equation is expressed as: For the gas inside the balloon: the gas inside the balloon is considered to be completely transparent. The gas does not absorb heat radiation from the outside and only transfers heat with the balloon membrane. The heat balance equation inside the balloon is expressed as: In the formula, m q is the mass of the gas, C q is the specific heat capacity of the gas, M a is the relative molecular mass of air, is the velocity of the balloon in the vertical direction; For balloon skin: The heat exchange of the skin includes the natural convection heat exchange Q1 between the inner surface of the skin and the gas inside the balloon, the ambient heat radiation absorbed by the outer surface of the skin, and the convection heat exchange with the ambient atmosphere. The heat balance equation of the skin is: Where Q1 is the natural convection heat transfer between the inner surface of the skin and the gas inside the balloon, Q2 is the convection heat transfer between the outer surface of the skin and the ambient atmosphere, Q3 is the external heat radiation, and Q4 is the heat radiation from the balloon surface to the outside.

5. The system according to any one of claims 1 to 4, characterized in that: In the computational fluid dynamics module, the real-time volume and shape data of the balloon are input into the 3D CAD modeling software to establish the geometric model of the high-altitude balloon and its deceleration device parachute; the geometric model is input into ICEM to establish the flow field mesh discrete model, the flow field is divided by tetrahedral mesh, and the flow field near the high-altitude balloon is encrypted; A flow field calculation model is established based on the flow field grid discrete model, and the velocity and pressure distribution of the flow field are obtained based on the flow field calculation. According to the pressure distribution change on the balloon surface, the aerodynamic characteristics change of the balloon is obtained by automatic integration through the flow field calculation software.

6. The system according to claim 5, characterized in that The flow field governing equation is: Where ρ is the density of the ambient fluid, t is the time, v is the velocity vector of the fluid, p is the pressure of the fluid, τ is the stress tensor, and f is the volume force on the fluid.

7. The system according to claim 6, characterized in that The density ρ of the ambient fluid is obtained according to the ideal gas state equation and is expressed as: Where P is the ambient flow field pressure, M is the molar mass of the ambient atmosphere, and T is the ambient gas temperature.

8. The system according to claim 1, characterized in that In the flight dynamics module, the force analysis of the balloon system is performed, and the dynamic equation is expressed as: Where M q is the mass of the balloon, M s is the mass of the parachute; M1 and M2 are the equivalent masses of the parachute of the balloon, i.e., the sum of the additional mass and the mass of the object; F dq 、F ds is the aerodynamic drag on the balloon and parachute; F is the buoyancy of the balloon; According to the real-time speed v, the height h of the balloon system is obtained: The aerodynamic force is obtained according to the real-time speed and aerodynamic characteristics, and the equation is: Where C is the aerodynamic characteristic, which is obtained by the computational fluid dynamics module.

9. The system according to claim 8, characterized in that The added mass of the balloon is expressed as: M add,q =C m ρV q In the formula, C m is the additional mass coefficient; The additional mass of the parachute is expressed as: In the formula, R t , C A , C t are the parachute projection radius, drag area and tangential aerodynamic coefficient respectively.

10. A method for predicting the shape and trajectory of a high-altitude balloon based on multidisciplinary integration, characterized in that: The steps include: Step 1, determine the inflation environment of the high-altitude balloon, and predict the real-time buoyancy, volume and shape changes of the high-altitude balloon during the high-altitude inflation and floating process after being filled according to the real-time altitude and speed motion parameters of the balloon, based on the function of the thermodynamic inflation analysis module, and according to the gas state equation and energy conservation equation; Step 2: According to the volume and shape of the balloon and based on the function of the computational fluid dynamics module, a geometric model, a grid model and a flow field calculation model of the balloon in the flow field are established to calculate the changes in the aerodynamic characteristics of the balloon; Step 3: Perform dynamic analysis on the balloon system. Based on the flight dynamics module function, the particle dynamics motion equation of the balloon is established according to the aerodynamic force and buoyancy of the balloon, and the speed and height change of the balloon are obtained; Step 4: Execute steps 1-3 at each time step, obtain all the information at that moment, iterate to the next time step, repeat steps 1-3, and then obtain the transient changes of balloon thermodynamics, aerodynamic characteristics and flight dynamics parameters.

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