A design method for the air supply flow rate of the blowdown branch pipe of a cryogenic liquid rocket

Abstract

The present invention relates to a method for designing the air supply flow rate of a blowdown branch pipe for a cryogenic liquid rocket. The method comprises the following steps: determining the propellant temperature, the geometric parameters of the cabin section, and the physical parameters of the cabin section materials according to the overall input, and determining the target average temperature of the air in the cabin section; determining the ambient temperature and the average ground wind speed on the launch day according to the overall input; calculating the convective heat transfer coefficient outside the cabin wall according to the input parameters; obtaining the value of the convective heat transfer coefficient inside the cabin wall; establishing a cabin section thermal grid model; and establishing a thermal grid model for each thermal grid based on the air supply flow rate m. in The heat balance equation is solved simultaneously based on the input conditions in the above steps to obtain the air supply flow rate. The design method of the present invention is fast and simple, and the design results are highly accurate. It can quickly calculate the air supply flow rate except for the branch pipe based on the environmental conditions on the launch day and the equipment parameters of the rocket compartment, providing input conditions for ground air supply and distribution, thereby ensuring the temperature environment of the individual equipment in the compartment.

Description

Technical Field

[0001] The present invention relates to the field of liquid rocket thermal environment design, and in particular to a method for designing the air supply flow rate of a blow-off branch pipe of a cryogenic liquid rocket. Background Art

[0002] After a small cryogenic rocket is erected and before launch, some sections, such as the inter-tank section, will be affected by the cryogenic propellant in the tank. The average temperature of the section can drop to dozens of degrees below zero. Excessively low temperature environment may cause the individual equipment in the section to fail to work properly or even be damaged. Therefore, a blowing system is needed to improve the thermal environment in the cabin before launch.

[0003] The blowdown system usually consists of ground gas supply and distribution equipment, transmission pipelines and blowdown branches in the cabin. The ground gas supply and distribution equipment supplies high-temperature gases such as hot nitrogen heated in a water bath, which are then transported to the required cabin section through the transmission pipeline. The high-temperature gas is discharged from the blowdown branch in the cabin section to maintain the ambient temperature in the cabin.

[0004] Generally, the design of the air supply flow rate of the blow-off branch pipe usually requires building a set of test products and determining it through experiments. This design process is relatively complicated and not universal.

[0005] In order to improve the design efficiency of the rocket's purge system, this paper proposes a design method for the air supply flow rate of the cabin purge branch pipe. This method is fast and simple, and the design results are highly accurate, which is of great reference value for the rocket's ground air supply and distribution. Summary of the Invention

[0006] The purpose of the present invention is to provide a fast and accurate design method for the air supply flow of the cryogenic liquid rocket blow-off branch pipe, to provide input conditions for ground air supply and distribution, thereby ensuring the temperature environment of the single equipment in the cabin.

[0007] To achieve the above object, the technical solution adopted by the present invention includes the following steps:

[0008] S1. Determine the propellant temperature T based on the overall input liq , the geometric parameters of the cabin and the physical parameters of the cabin materials, and determine the target average temperature T of the air in the cabin air ;

[0009] S2. Determine the ambient temperature T on the launch day based on the overall input env and the average surface wind speed v;

[0010] S3. Calculate the convective heat transfer coefficient h outside the bulkhead based on the input parameters in step S2. out ;

[0011] S4, Convective heat transfer coefficient h inside the bulkhead in The value range is 1-10W / m2 , the value is determined based on the standard of making the heat loss in the cabin greater or the heat inflow smaller;

[0012] S5. Based on the input conditions of step S1, a cabin thermal grid model is established;

[0013] S6. Establish a gas supply flow m for each heat grid. in The heat balance equation is solved simultaneously according to the input conditions of steps S1-S4 to obtain the gas flow rate m in .

[0014] Furthermore, in step S3, the convective heat transfer coefficient h outside the bulkhead is out The calculation method is as follows:

[0015] First, based on the average ground wind speed v at the launch site and the ambient temperature T on the launch date env As the reference temperature T m , use the following formula to calculate the Reynolds number Re at the reference temperature m :

[0016] Re m =ρ m vd / μ m

[0017] Where:

[0018] ρ m ——reference density of air, according to T m Obtained by looking up the table;

[0019] d——tank diameter;

[0020] μ m ——Air reference dynamic viscosity coefficient, according to T m Obtained by looking up the table.

[0021] According to the Reynolds number, the Nusselt number Nu is calculated using the following formula: m :

[0022]

[0023] Where:

[0024] Pr m ——Prandtl number, according to T m Obtained by looking up the table.

[0025] Finally, the convective heat transfer coefficient outside the bulkhead h is obtained by the following formula: out :

[0026]

[0027] Where:

[0028] d——tank diameter;

[0029] λ m ——Thermal conductivity of air, according to T m Obtained by looking up the table.

[0030] Furthermore, in step S4, the convective heat transfer coefficient is set based on the standard of making the heat loss in the cabin greater or the heat inflow smaller. Specifically, if the ambient temperature is lower than the target temperature in the cabin, the internal convective heat transfer coefficient is set to 10W / m 2 , to ensure maximum heat loss to the outside; if the ambient temperature is higher than the target temperature in the cabin, the internal convection heat transfer coefficient is 1W / m 2 , ensuring that the heat transfer inward is minimized.

[0031] Furthermore, in step S5, the method for establishing the cabin thermal grid model is specifically as follows:

[0032] For the cylindrical intertank section, i.e., the cabin section, the intertank section includes the front and rear bottoms of the tank, the bulkhead, the thermal protection layer, and the air within the intertank section. In the actual intertank section model, the front and rear bottoms of the tank are connected to the bulkhead and made of the same material. The thermal protection layer laid on the front and rear bottoms of the tank is used for insulation. The actual model is divided into two dimensions by topology to obtain a thermal grid model. The grid size and physical properties correspond to the actual model.

[0033] Furthermore, the grid size and physical parameters of the cabin thermal grid model correspond to the actual model. The specific corresponding method is:

[0034] First, the naming rules of each grid are clarified: X is the radial direction of the compartment, Y is the axial direction of the compartment, and the four sides of the thermal grid are specified as N, E, W, and S, respectively. Among them, Δy is the length of the grid in the y direction, and its corresponding area is A. y , Δx is the length of the grid in the x direction, and its corresponding area is A x , the corresponding area refers to the actual three-dimensional area represented by the edge of the two-dimensional figure after mapping the three-dimensional geometric body to the two-dimensional figure;

[0035] The physical parameters of each thermal grid include the average temperature T and thermal conductivity λ of the grid, the thermal conductivity λ of the compartment C , thermal conductivity of heat protection layer λ FRC .

[0036] Furthermore, in step S6, when the purge system reaches a steady state, the gas and solid heat conduction temperature fields remain unchanged, and only the heat conduction process exists inside. The heat flowing into the heat grid is the same as the heat flowing out. The difference between each grid is only that the boundary conditions of each side of the grid are different. On this basis, the heat balance equation of each side of each grid is first established, and then the heat balance equation of each grid is established. The average temperature of each grid is obtained by solving the average temperature of the grid corresponding to the air in the compartment, T air is the input parameter determined in step S1. Finally, the heat balance equation of the entire grid model is established to solve the gas flow rate m in .

[0037] Compared with the existing technology, the present invention proposes a design method for the air supply flow rate of the branch pipe in the cabin. This method is fast and simple, and the design results are highly accurate. The air supply flow rate of the branch pipe can be quickly calculated according to the environmental conditions on the launch day and the equipment parameters of the rocket cabin, providing input conditions for ground air supply and distribution, thereby ensuring the temperature environment of the single equipment in the cabin.

[0038] The design method of the air supply flow rate of the blow-off branch pipe of the present invention is universal. There is no need to build a test product during the rocket design stage to determine the air supply flow rate through experiments, which reduces the complexity of the design process and further reduces the cost of rocket launch. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the thermal grid model of the compartment section of the present invention, wherein Figure (a) is the actual model of the compartment section, and Figure (b) is the thermal grid model of the compartment section;

[0040] Figure 2 Schematic diagram of the grid size of the cabin thermal grid model of the present invention;

[0041] Figure 3 Schematic diagram of the thermal grid geometric mapping relationship of the cabin thermal grid model of the present invention.

[0042] Explanation of symbols: 1-front bottom of the tank, 2-rear bottom of the tank, 3-rear bottom thermal protection layer, 4-cabin air, 5-bulkhead, 6-front bottom thermal protection layer. DETAILED DESCRIPTION

[0043] S1. Determine the propellant temperature T based on the overall input liq , the geometric parameters of the cabin and the physical parameters of the cabin materials, and determine the target average temperature T of the air in the cabin air ;

[0044] S2. Determine the ambient temperature T on the launch day based on the overall input env and the average surface wind speed v;

[0045] S3. Calculate the convective heat transfer coefficient h outside the bulkhead based on the input parameters in step S2. out ;

[0046] S4, Convective heat transfer coefficient h inside the bulkhead in The value range is 1-10W / m 2 , the value is determined based on the standard of making the heat loss in the cabin greater or the heat inflow smaller;

[0047] S5. Based on the input conditions of step S1, a cabin thermal grid model is established;

[0048] S6. Establish a gas supply flow m for each heat grid. in The heat balance equation is solved simultaneously according to the input conditions of steps S1-S4 to obtain the gas flow rate m in .

[0049] Furthermore, in step S3, the convective heat transfer coefficient h outside the bulkhead is out The calculation method is as follows:

[0050] First, based on the average ground wind speed v at the launch site and the ambient temperature T on the launch date env As the reference temperature T m , use the following formula to calculate the Reynolds number Re at the reference temperature m :

[0051] Re m =ρ m vd / μ m

[0052] Where:

[0053] ρ m ——reference density of air, according to T m Obtained by looking up the table;

[0054] d——tank diameter;

[0055] μ m ——Air reference dynamic viscosity coefficient, according to T m Obtained by looking up the table.

[0056] According to the Reynolds number, the Nusselt number Nu is calculated using the following formula: m :

[0057]

[0058] Where:

[0059] Pr m ——Prandtl number, according to T m Obtained by looking up the table.

[0060] Finally, the convective heat transfer coefficient outside the bulkhead h is obtained by the following formula: out :

[0061]

[0062] Where:

[0063] d——tank diameter;

[0064] λ m ——Thermal conductivity of air, according to T m Obtained by looking up the table.

[0065] Furthermore, in step S4, the convective heat transfer coefficient is set based on the standard of making the heat loss in the cabin greater or the heat inflow smaller. Specifically, if the ambient temperature is lower than the target temperature in the cabin, the internal convective heat transfer coefficient is set to 10W / m 2 , to ensure maximum heat loss to the outside; if the ambient temperature is higher than the target temperature in the cabin, the internal convection heat transfer coefficient is 1W / m 2 , ensuring that the heat transfer inward is minimized.

[0066] Furthermore, in step S5, taking a cylindrical intertank section of a certain type of rocket (i.e., the cabin section between two cryogenic storage tanks of the rocket) as an example, the intertank section includes the front bottom of the tank, the rear bottom of the tank, the bulkhead, the heat protection layer, and the air in the intertank section, a method for establishing a cabin section thermal grid model is described in the attached Figure 1 As shown, specifically:

[0067] Figure a is the actual model of the intertank section, and Figure b is the thermal grid model of the intertank section. In the actual intertank section model, the front and rear bottoms of the tank are connected to the bulkhead and made of the same material. The thermal insulation layer laid on the front and rear bottoms of the tank is used for thermal insulation. The actual model is divided into two dimensions to obtain the thermal grid model. The grid size and physical parameters correspond to the actual model. That is, thermal grid 2 is the rear bottom of the tank, grid 13 is the front bottom of the tank, grids 1, 3, 4, 6, 7, 8, 9, 11, 12, and 14 are the bulkhead, grids 5 and 10 are the thermal insulation layer, and Air is the air in the cabin.

[0068] Furthermore, the grid size and physical parameters of the cabin thermal grid model correspond to the actual model. The corresponding method is as follows: first, the naming rule of each grid is clarified: the four edges of the thermal grid are specified as N, E, W, and S, respectively, such as Figure 2 As shown, where Δy is the length of the grid in the y direction, and its corresponding area is A y , Δx is the length of the grid in the x direction, and its corresponding area is A x , the corresponding area refers to the actual three-dimensional area represented by the edge of the two-dimensional figure after mapping the three-dimensional geometric body to the two-dimensional figure;

[0069] Combined with attachment Figure 3The accompanying figure illustrates the mapping relationship of the thermal grid geometric parameters, taking the cabin section outer diameter as d, the bulkhead thickness as a, and the rear bottom insulation layer thickness as b. D Taking thermal grid 5 as an example, it corresponds to the actual rear bottom insulation layer, Δx is the inner diameter of the cabin d-2a, Δy is the thickness of the insulation layer b D , A x is the area of a circle with a diameter of d-2a, i.e. π(d-2a) 2 / 4,A y For height b D , half the outer surface area of a cylinder with a diameter of d-2a, that is, π(d-2a)b D / 2, and the length and area of the remaining thermal grids are determined in a similar manner to that of thermal grid 5.

[0070] The physical parameters of each thermal grid include the average temperature T and thermal conductivity λ of the grid. The thermal conductivity of grid 1 is the thermal conductivity λ of the compartment. C , the thermal conductivity of grid 2 is the thermal conductivity of the heat protection layer λ FRC .

[0071] Furthermore, in step S6, the input conditions of steps S1, S2, S3 and S4 are solved simultaneously to obtain the gas supply flow rate. The basic principle of thermal balance is: when the purge system reaches a steady state, the gas and solid heat conduction temperature field remains unchanged, and only the heat conduction process exists inside. The heat flowing into the heat grid is the same as the heat flowing out, that is, for each grid, Q out =Q in The only difference between each grid is the different boundary conditions on each side of the grid. On this basis, the heat balance equation of each grid is established. Figure 1 The four typical thermal grids in (b) are used as an example to illustrate the method of establishing the heat balance equation. The heat balance equations of the remaining grids can be derived from the four typical thermal grids.

[0072] (a) Grid 1 heat balance equation:

[0073] N side (temperature boundary):

[0074] W side (external convection heat transfer boundary):

[0075] E-side (internal heat conduction boundary):

[0076] S side (internal heat conduction boundary):

[0077] Heat balance equation: Q out_N +Q out_E =Q in_S +Q in_W .

[0078] (b) Grid 7 heat balance equation:

[0079] N side (internal thermal boundary):

[0080] W side (external convection heat transfer boundary):

[0081] E side (internal convection heat transfer boundary):

[0082] S side (internal heat conduction boundary):

[0083] Heat balance equation: Q out_N +Q out_S =Q in_E +Q in_W .

[0084] (c) Grid 5 heat balance equation:

[0085] N side (internal thermal boundary):

[0086] W-side (internal heat conduction boundary):

[0087] E-side (internal heat conduction boundary):

[0088] S side (internal convection heat transfer boundary):

[0089] Heat balance equation: Q out_N +Q out_W +Q out_E =Q in_S .

[0090] By solving the heat balance equation, the average temperature of each grid can be obtained, and the average temperature of the Air grid T air is the input parameter determined in step S1;

[0091] (d) Air heat balance equation:

[0092] Q in =m in c p T in ;

[0093]

[0094] Where:

[0095] m in ——gas supply flow rate;

[0096] c p —Specific heat capacity of the supplied gas;

[0097] T in ——The temperature of the gas supplied.

[0098] Heat balance equation: Q out =Q in , we can solve for the gas flow rate m in .

Claims

1. A method for designing the air supply flow rate of a cryogenic liquid rocket blowdown branch pipe, characterized in that: The calculation steps include: S1. Determine the propellant temperature T based on the overall input liq , the geometric parameters of the cabin and the physical parameters of the cabin materials, and determine the target average temperature T of the air in the cabin air ; S2. Determine the ambient temperature T on the launch day based on the overall input env and the average surface wind speed v; S3. Calculate the convective heat transfer coefficient h outside the bulkhead based on the input parameters in step S2. out ; S4, Convective heat transfer coefficient h inside the bulkhead in The value range is 1-10W / m 2 , the value is determined based on the standard of making the heat loss in the cabin greater or the heat inflow smaller; S5. Based on the input conditions of step S1, a cabin thermal grid model is established; The grid size and physical parameters of the cabin thermal grid model correspond to the actual model. The specific correspondence method is as follows: First, the naming rules of each grid are clarified: X is the radial direction of the compartment, Y is the axial direction of the compartment, and the four sides of the thermal grid are specified as N, E, W, and S, respectively. Among them, Δy is the length of the grid in the y direction, and its corresponding area is A. y , Δx is the length of the grid in the x direction, and its corresponding area is A x , the corresponding area refers to the actual three-dimensional area represented by the edge of the two-dimensional figure after mapping the three-dimensional geometric body to the two-dimensional figure; The physical parameters of each thermal grid include the average temperature T and thermal conductivity λ of the grid, the thermal conductivity λ of the compartment C , thermal conductivity of heat protection layer λ FRC ; S6. Establish a gas flow rate m for each heat grid. in The heat balance equation is solved simultaneously according to the input conditions of steps S1-S4 to obtain the gas flow rate m in .

2. The method for designing the air supply flow rate of a cryogenic liquid rocket blowdown branch pipe according to claim 1, characterized in that: In step S3, the convective heat transfer coefficient h outside the bulkhead out The calculation method is as follows: First, based on the average ground wind speed v at the launch site and the ambient temperature T on the launch date env As the reference temperature T m , use the following formula to calculate the Reynolds number Re at the reference temperature m : Re m =ρ m vd / m m Where: ρ m ——reference density of air, according to T m Obtained by looking up the table; d——tank diameter; μ m ——Air reference dynamic viscosity coefficient, according to T m Obtained by looking up the table; According to the Reynolds number, the Nusselt number Nu is calculated using the following formula: m : Where: Pr m ——Prandtl number, according to T m Obtained by looking up the table; Finally, the convective heat transfer coefficient outside the bulkhead h is obtained by the following formula: out : Where: d——tank diameter; λ m ——Thermal conductivity of air, according to T m Obtained by looking up the table.

3. The method for designing the air supply flow rate of a cryogenic liquid rocket blowdown branch pipe according to claim 1, characterized in that: In step S4, the convective heat transfer coefficient is set based on the standard of making the heat loss in the cabin greater or the heat inflow smaller. Specifically, if the ambient temperature is lower than the target temperature in the cabin, the convective heat transfer coefficient inside the cabin wall is set to 10W / m 2 , to ensure maximum heat loss to the outside; if the ambient temperature is higher than the target temperature inside the bulkhead, the internal convection heat transfer coefficient is 1W / m 2 , ensuring that the heat transfer inward is minimized.

4. The method for designing the air supply flow rate of a cryogenic liquid rocket blowdown branch pipe according to claim 1, characterized in that: In step S5, the method for establishing the cabin thermal grid model is specifically as follows: For the cylindrical intertank section, i.e., the cabin section, the intertank section includes the front and rear bottoms of the tank, the bulkhead, the thermal protection layer, and the air within the intertank section. In the actual intertank section model, the front and rear bottoms of the tank are connected to the bulkhead and made of the same material. The thermal protection layer laid on the front and rear bottoms of the tank is used for insulation. The actual model is divided into two dimensions by topology to obtain a thermal grid model. The grid size and physical properties correspond to the actual model.

5. The method for designing the air supply flow rate of a cryogenic liquid rocket blowdown branch pipe according to claim 1, characterized in that: In step S6, when the purge system reaches a steady state, the gas and solid heat conduction temperature fields remain unchanged, and only the heat conduction process exists inside. The heat flowing into the heat grid is the same as the heat flowing out. The difference between each grid is only the boundary conditions of each side of the grid. On this basis, the heat balance equation of each side of each grid is first established, and then the heat balance equation of each grid is established. The average temperature of each grid is obtained by solving the average temperature of the grid corresponding to the air in the compartment, T air is the input parameter determined in step S1. Finally, the heat balance equation of the entire grid model is established to solve the gas flow rate m in .

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