Method for calculating air permeability of parachute canopy under high pressure difference condition

Abstract

The invention relates to the technical field of air permeability of parachute canopies, in particular to a method for calculating air permeability of a parachute canopy under a high pressure difference condition, which comprehensively considers weaving structure characteristics of a canopy fabric, gas compressibility under the high pressure difference condition and conditions and working conditions during supersonic flight of a parachute. The method for rapidly calculating the air permeability of the parachute canopy under the specified high pressure difference condition is established. According to the method, a more accurate mathematical model can be provided for air permeability numerical simulation calculation, canopy engineering design and the like of the parachute under the supersonic speed and high pressure difference conditions, and guidance is provided for research and design of the parachute.

Description

Technical Field

[0001] The present invention relates to the technical field of the air permeability of a parachute canopy, and particularly relates to a method for calculating the air permeability of a parachute canopy under high pressure difference conditions. Background Art

[0002] As a traditional decelerator, a parachute has the characteristics of small system mass and high aerodynamic deceleration efficiency. In addition to being used for personnel airdropping, it has also been widely applied in the fields of equipment airdropping and spacecraft landing deceleration. In recent years, with the advancement of projects such as planetary exploration and deep space sampling return by major spacefaring countries, the demand for supersonic parachute deceleration technology has become increasingly strong. Theory and practice have shown that the air permeability of the canopy has an important impact on both the inflation and deceleration performance of the parachute.

[0003] Researchers have carried out relevant research on the prediction of the air permeability of parachute canopy fabrics by using various means such as wind tunnel tests, flight tests, and theoretical research. Researchers have found that the Ergun theory based on the porous medium model shows good applicability in predicting the air permeability of parachute canopies at low speeds, and the Ergun theory model has been widely used in the simulation of the air permeability of low-speed parachutes.

[0004] In the future, as the flight speed of deep space probes further increases, they will face higher Mach number deceleration problems when entering the planetary atmosphere or sampling and returning to re-enter the Earth's atmosphere. In low-altitude high-dynamic pressure deceleration missions on Earth, such as the dispensing of submunitions, the working dynamic pressure of the deceleration parachute of the aircraft is higher, and the pressure difference between the inside and outside of the canopy is larger than that of a conventional parachute. Under high-pressure difference conditions, the pore flow velocity of the parachute canopy is relatively large, and it can no longer be simply regarded as low-speed incompressible flow. At the same time, the pore flow of the canopy will experience choking under certain pressure difference conditions. The current Ergun theory-based calculation model for the air permeability of parachute canopies fails to consider the compressibility of the gas under high pressure difference conditions and the flow choking problem under high pressure difference conditions. Therefore, the present invention provides a method for calculating the air permeability of a parachute canopy, which considers high pressure difference conditions and establishes a calculation method for the air permeability of a parachute canopy with mass flow as an index. Summary of the Invention

[0005] In order to solve the deficiencies in the above background art, the present invention provides a method for calculating the air permeability of a parachute canopy under high pressure difference conditions, which can provide a more accurate mathematical model for the numerical simulation calculation of the air permeability of a parachute under supersonic and high pressure difference conditions, and provide guidance for the research and design of parachutes.

[0006] The first object of the present invention is to provide a method for calculating the air permeability of a parachute canopy under high pressure difference conditions, including:

[0007] Under the specified test pressure difference conditions, measure the air permeability of the parachute canopy fabric to obtain the air permeability of the canopy fabric under the test pressure difference;

[0008] Obtain the projected area of the pore region of the parachute canopy fabric;

[0009] According to the total pressure, total temperature of the parachute flight condition, as well as the specific heat ratio of the atmosphere, gas constant, and the projected area of the pore region of the parachute canopy fabric, obtain the maximum air permeability of the parachute canopy fabric;

[0010] Obtain the critical pressure difference at which the parachute canopy fabric reaches the maximum air permeability;

[0011] According to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtain the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability.

[0012] Preferably, according to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtaining the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability includes:

[0013] When the pressure difference of the parachute in the high-pressure difference environment ≤ the critical pressure difference, the air permeability of the parachute in the high-pressure difference environment is calculated as follows:

[0014] q = 2tq max -t 2 q max

[0015] where t ∈ [0, 1], and is calculated by the following formula:

[0016] ΔP = 2t(1 - t)q max ΔP1 / q1 + t 2 ΔP2

[0017] In the formula, q is the air permeability of the parachute in the high-pressure difference environment; q max is the maximum air permeability; ΔP is the pressure difference of the parachute in the high-pressure difference environment; ΔP1 is the test pressure difference; q1 is the air permeability of the parachute canopy fabric under the test pressure difference; ΔP2 is the critical pressure difference.

[0018] Preferably, according to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtaining the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability includes: when the pressure difference of the parachute in the high-pressure difference environment > the critical pressure difference, the air permeability of the parachute in the high-pressure difference environment is equal to the maximum air permeability.

[0019] Preferably, the critical pressure difference at which the parachute canopy fabric reaches the maximum air permeability is obtained according to the one-dimensional steady compressible nozzle flow theory and the total pressure of the parachute flight condition.

[0020] Preferably, the projected area of the pore region of the parachute canopy fabric is obtained according to the ratio of the projected area of the pore region of the parachute canopy fabric to the total area of the parachute canopy.

[0021] Preferably, the maximum air permeability of the parachute canopy fabric is calculated as follows:

[0022]

[0023] In the formula, P0 is the total pressure under the parachute flight condition; T0 is the total temperature; γ is the atmospheric specific heat ratio; R is the gas constant; A p is the projected area of the pore region of the parachute canopy fabric; q max is the maximum air permeability.

[0024] Preferably, the air permeability of the parachute canopy fabric under the test pressure difference is calculated as follows:

[0025] q1 = V1Aρ

[0026] In the formula, V1 is the gas flow rate during the test; ρ is the air density during the test; A is the area of the parachute canopy fabric.

[0027] The second object of the present invention is to provide a computer program product, including a computer program, which when executed by a processor, implements the above-mentioned method for calculating the air permeability of a parachute canopy under high pressure difference conditions.

[0028] The third object of the present invention is to provide an electronic device, including:

[0029] a processor; and

[0030] a memory for storing executable instructions of the processor;

[0031] wherein, the processor is configured to execute the above-mentioned method for calculating the air permeability of a parachute canopy under high pressure difference conditions by executing the executable instructions.

[0032] The fourth object of the present invention is to provide a system for calculating the air permeability of a parachute canopy under high pressure difference conditions, including:

[0033] a test module for measuring the air permeability of the parachute canopy fabric under the specified test pressure difference conditions to obtain the air permeability of the parachute canopy fabric under the test pressure difference;

[0034] a critical data module for obtaining the projected area of the pore region of the parachute canopy fabric; obtaining the maximum air permeability of the parachute canopy fabric according to the total pressure, total temperature under the parachute flight condition, and the atmospheric specific heat ratio, gas constant and the projected area of the pore region of the parachute canopy fabric; obtaining the critical pressure difference at which the parachute canopy fabric reaches the maximum air permeability;

[0035] an air permeability calculation module for obtaining the air permeability of the parachute in the high pressure difference environment through the maximum air permeability according to the difference between the pressure difference and the critical pressure difference of the parachute in the high pressure difference environment.

[0036] The present invention has at least the following beneficial effects:

[0037] The present invention provides a method for calculating the ventilation rate of a parachute canopy under high pressure difference conditions. This method comprehensively considers the characteristics of orifice jet flow of the canopy pores under high pressure difference conditions and the compressibility of gas during high-speed flow. Based on one-dimensional steady compressible nozzle flow and the second-order Bessel method, it can quickly and conveniently obtain the ventilation rate value of the parachute canopy under high pressure difference conditions, thereby providing support and guidance for further research on the breathability of parachutes and parachute design.

[0038] Each parameter involved in the calculation method of the present invention is only related to the fabric structure of the canopy and the test parameters. For a determined parachute canopy object, the required parameters are known values or can be obtained through simple tests, and the mathematical model of the ventilation rate of the parachute canopy under high pressure difference conditions can be obtained quickly and conveniently. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a flowchart of a method for calculating the ventilation rate of a parachute canopy under high pressure difference conditions provided by the present invention.

[0040] Figure 2 It is a pressure difference - ventilation rate curve graph for comparison between simulation experiments, Ergun theory, and the method provided by the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] In order to elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following will be described in detail in conjunction with embodiments.

[0042] The purpose of the present invention is to provide a method for calculating the ventilation rate of a parachute canopy under high pressure difference conditions, which can provide a more accurate mathematical model for numerical simulation calculation of the breathability of parachutes under supersonic and high pressure difference conditions, and provide guidance for the research and design of parachutes.

[0043] It should be noted that the high pressure difference condition refers to the condition where the gas flow velocity passing through the canopy under this pressure difference exceeds the compressibility of the gas under incompressible conditions and cannot be ignored.

[0044] In order to achieve the above purpose, as shown in Figure 1 A method for calculating the ventilation rate of a parachute canopy under high pressure difference conditions includes:

[0045] S1. Under the specified test pressure difference conditions, measure the breathability of the parachute canopy fabric to obtain the ventilation rate of the canopy fabric under the test pressure difference;

[0046] The ventilation rate of the canopy fabric under the test pressure difference is calculated by the following formula:

[0047] q1 = V1Aρ

[0048] Wherein, V is the gas flow rate during the test; ρ is the air density during the test; A is the area of the parachute fabric.

[0049] S2. Obtain the projected area of the pore region of the parachute fabric;

[0050] The projected area of the pore region of the parachute fabric is obtained according to the ratio of the projected area of the pore region of the parachute fabric to the total area of the parachute.

[0051] S3. Obtain the maximum air permeability of the parachute fabric according to the total pressure, total temperature of the parachute flight condition, the atmospheric specific heat ratio, the gas constant and the projected area of the pore region of the parachute fabric;

[0052] The formula for the maximum air permeability of the parachute fabric is as follows:

[0053]

[0054] Wherein, P0 is the total pressure of the parachute flight condition; T0 is the total temperature; γ is the atmospheric specific heat ratio; R is the gas constant; A p is the projected area of the pore region of the parachute fabric; q max is the maximum air permeability.

[0055] S4. Obtain the critical pressure difference at which the parachute fabric reaches the maximum air permeability;

[0056] The critical pressure difference at which the parachute fabric reaches the maximum air permeability is obtained according to the one-dimensional steady compressible nozzle flow theory and the total pressure of the parachute flight condition.

[0057] S5. Obtain the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability according to the difference between the pressure difference and the critical pressure difference of the parachute in the high-pressure difference environment.

[0058] Obtaining the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability according to the difference between the pressure difference and the critical pressure difference of the parachute in the high-pressure difference environment includes:

[0059] When the pressure difference of the parachute in the high-pressure difference environment ≤ the critical pressure difference, the air permeability of the parachute in the high-pressure difference environment is calculated as follows:

[0060] q = 2tq max -t 2 q max

[0061] wherein, t ∈ [0, 1], and is calculated by the following formula:

[0062] ΔP = 2t(1 - t)q max ΔP1 / q1 + t 2 ΔP2

[0063] Wherein, q is the air permeability of the parachute in a high-pressure difference environment, and this air permeability is the air permeability under mass flow, and its unit is kg / s; q max is the maximum air permeability; ΔP is the pressure difference of the parachute in a high-pressure difference environment; ΔP1 is the test pressure difference; q1 is the air permeability of the parachute fabric under the test pressure difference; ΔP2 is the critical pressure difference.

[0064] According to the difference between the pressure difference of the parachute in a high-pressure difference environment and the critical pressure difference, the air permeability of the parachute in a high-pressure difference environment is obtained through the maximum air permeability, including: when the pressure difference of the parachute in a high-pressure difference environment > the critical pressure difference, the air permeability of the parachute in a high-pressure difference environment is equal to the maximum air permeability.

[0065] To illustrate the purpose of the present invention, the present invention designs a method for calculating the air permeability of a parachute canopy under high-pressure difference conditions, which is used to calculate the air permeability of the parachute canopy under target pressure difference conditions. This method includes the following steps:

[0066] 1) According to the air permeability measurement result V1 of the parachute fabric when the test pressure difference is ΔP1 and the air density ρ during the test, according to the following formula:

[0067] q1 = V1Aρ

[0068] Obtain the mass flow air permeability data q1 of the parachute fabric with an area of A. Denote the air permeability q1 when the pressure difference is ΔP1 as the characteristic point P1(ΔP1, q1).

[0069] It should be noted that the air permeability measurement is based on the national standard GB / T 5453 Determination of Air Permeability of Textiles, and the national standard recommends pressure drops, that is, the pressure difference between the two sides of the fabric (test pressure difference) is 50 Pa, 100 Pa, 200 Pa, and 500 Pa.

[0070] 2) According to the ratio ε of the projected area of the pore region of the parachute fabric to the total area of the parachute canopy A , and through the following formula:

[0071] A p = Aε A

[0072] Calculate the projected area A of the pore region of the parachute fabric with an area of A p .

[0073] 3) According to the total pressure P0, total temperature T0, specific heat ratio γ of the atmosphere, gas constant R of the parachute flight condition and the projected area A of the pore region of the parachute fabric obtained in the second step p , according to the following formula:

[0074]

[0075] Calculate the maximum air permeability q of the parachute fabric max .

[0076] 4) According to the one-dimensional steady compressible nozzle flow theory and the total pressure P0 of the parachute flight condition, obtain the critical pressure difference ΔP2 at which the parachute fabric reaches the maximum air permeability:

[0077] ΔP2 = 0.5283P0

[0078] Mark the point where the parachute fabric reaches the maximum air permeability at the critical pressure difference as the characteristic point P2(ΔP2, q max ).

[0079] 5) According to the characteristic point P1(ΔP1, q1) obtained in the first step and the maximum air permeability q of the parachute fabric obtained in the third step max , calculate the control points of the curve of the relationship between air permeability and pressure difference

[0080] 6) According to the control points obtained in the fifth step and the characteristic point P2(ΔP2, q max ), the calculation method of the air permeability of the parachute canopy under high pressure difference conditions can be obtained:

[0081] When the pressure difference ΔP ≤ ΔP2, the air permeability q of the parachute canopy and the pressure difference ΔP satisfy the following relationship:

[0082]

[0083] When the pressure difference ΔP > ΔP2, the air permeability q of the parachute canopy and the pressure difference ΔP satisfy the following relationship:

[0084]

[0085] Taking a certain type of parachute as an example in the present invention, the parachute canopy material is K58326-3 anti-burning red silk lattice silk. From the air permeability measurement test and the knitting method of the parachute fabric, it can be known that: the air permeability speed of this parachute canopy material at the pressure difference ΔP1 = 100 Pa is V1 = 0.486 m / s, and the ratio ε of the projected area of the pore region of the parachute fabric to the total area of the parachute canopy A = 5.7194%. Set the flight condition as: total pressure P0 = 101325 Pa, total temperature T0 = 288.1499 K, atmospheric specific heat ratio γ = 1.4, gas constant R = 287.053 m 2 / (s 2 K). Executing steps 1-5 can obtain 2 characteristic points and 1 control point: P1(100 Pa, 0.5954 m / s), P2(53530 Pa, 13.7974 m / s), P 12(2318Pa, 13.7974m / s). By performing the sixth step, the air permeability value of the parachute canopy under high pressure difference conditions can be obtained. The air permeability value per unit area of the parachute canopy is calculated and compared with the calculation results based on the Ergun equation of porous medium theory and the results of numerical simulation tests on the canopy fabric as shown in Table 1 below.

[0086] Table 1 Comparison of the results of simulation tests

[0087]

[0088] The overall comparison is plotted as Figure 2 shown. It can be seen that under high pressure difference conditions, the calculation result of the air permeability by the Ergun theory deviates seriously, and the present invention has good applicability.

[0089] The present invention provides a computer program product, including a computer program which, when executed by a processor, implements the above-mentioned method for calculating the air permeability of a parachute canopy under high pressure difference conditions.

[0090] The present invention provides an electronic device, including:

[0091] a processor; and

[0092] a memory for storing executable instructions of the processor;

[0093] wherein the processor is configured to execute the above-mentioned method for calculating the air permeability of a parachute canopy under high pressure difference conditions by executing the executable instructions.

[0094] The present invention provides a system for calculating the air permeability of a parachute canopy under high pressure difference conditions, including:

[0095] a test module for measuring the air permeability of the canopy fabric of the parachute under specified test pressure difference conditions to obtain the air permeability of the canopy fabric under the test pressure difference;

[0096] a critical data module for obtaining the projected area of the pore region of the canopy fabric; obtaining the maximum air permeability of the canopy fabric according to the total pressure, total temperature of the parachute flight condition, as well as the specific heat ratio of the atmosphere, gas constant and the projected area of the pore region of the canopy fabric; obtaining the critical pressure difference at which the canopy fabric reaches the maximum air permeability;

[0097] an air permeability calculation module for obtaining the air permeability of the parachute in a high pressure difference environment through the maximum air permeability according to the difference between the pressure difference of the parachute in a high pressure difference environment and the critical pressure difference.

[0098] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for calculating the air permeability of a parachute canopy under high differential pressure conditions, characterized in that, Comprising: Under the condition of a specified test pressure difference, the air permeability of the parachute canopy fabric is measured to obtain the air permeability of the canopy fabric under the test pressure difference; Obtain the projected area of the pore region of the canopy fabric; According to the total pressure, total temperature of the parachute flight condition, as well as the specific heat ratio of the atmosphere, gas constant and the projected area of the pore region of the canopy fabric, obtain the maximum air permeability of the canopy fabric; Obtain the critical pressure difference at which the canopy fabric reaches the maximum air permeability; According to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtain the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability.

2. The method for calculating the air permeability of a parachute canopy under high differential pressure conditions according to claim 1, characterized in that, According to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtain the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability, including: When the pressure difference of the parachute in the high-pressure difference environment ≤ the critical pressure difference, the air permeability of the parachute in the high-pressure difference environment is calculated as follows: q = 2tq max -t 2 q max Where t ∈ [0,1], it is calculated by the following formula: ΔP = 2t(1 - t)q max ΔP1 / q1 + t 2 ΔP2 Wherein, q is the air permeability of the parachute in a high-pressure difference environment; q max is the maximum air permeability; ΔP is the pressure difference of the parachute in a high-pressure difference environment; ΔP1 is the test pressure difference; q1 is the air permeability of the parachute fabric under the test pressure difference; ΔP2 is the critical pressure difference.

3. The method for calculating the air permeability of a parachute canopy under high pressure difference conditions according to claim 1, wherein According to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference, obtain the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability, including: when the pressure difference of the parachute in the high-pressure difference environment > the critical pressure difference, the air permeability of the parachute in the high-pressure difference environment is equal to the maximum air permeability.

4. The method for calculating the air permeability of a parachute canopy under high differential pressure conditions according to claim 1, characterized in that, The critical pressure difference at which the canopy fabric reaches the maximum air permeability is obtained according to the one-dimensional steady compressible nozzle flow theory and the total pressure of the parachute flight condition.

5. The method for calculating the air permeability of a parachute canopy under high differential pressure conditions according to claim 1, wherein The projected area of the pore region of the canopy fabric is obtained according to the ratio of the projected area of the pore region of the canopy fabric to the total area of the canopy.

6. The method for calculating the air permeability of a parachute canopy under high differential pressure conditions according to claim 1, characterized in that, The maximum air permeability of the canopy fabric, the calculation formula is as follows: Wherein, P0 is the total pressure of the parachute flight condition; T0 is the total temperature; γ is the atmospheric specific heat ratio; R is the gas constant; A p is the projected area of the pore region of the parachute fabric; q max is the maximum air permeability.

7. The method for calculating the air permeability of a parachute canopy under high differential pressure conditions according to claim 1, characterized in that, The air permeability of the canopy fabric under the test pressure difference, the calculation formula is as follows: q1 = V1Aρ In the formula, V1 is the gas flow velocity during the test, that is, the air permeability of the fabric characterized by the flow velocity; ρ is the air density during the test; A is the area of the canopy fabric.

8. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the method for calculating the air permeability of the parachute canopy under the high-pressure difference condition described in any one of claims 1 to 7.

9. An electronic device, characterized in that, Comprising: A processor; And A memory for storing executable instructions of the processor; Wherein, the processor is configured to execute the method for calculating the air permeability of the parachute canopy under the high-pressure difference condition described in any one of claims 1 to 7 by executing the executable instructions.

10. A parachute canopy air permeability calculation system under high pressure difference conditions, characterized in that Comprising: A test module for measuring the air permeability of the parachute canopy fabric under the condition of a specified test pressure difference to obtain the air permeability of the canopy fabric under the test pressure difference; A critical data module for obtaining the projected area of the pore region of the canopy fabric; According to the total pressure, total temperature of the parachute flight condition, as well as the specific heat ratio of the atmosphere, gas constant and the projected area of the pore region of the canopy fabric, obtain the maximum air permeability of the canopy fabric; Obtain the critical pressure difference at which the canopy fabric reaches the maximum air permeability; An air permeability calculation module for obtaining the air permeability of the parachute in the high-pressure difference environment through the maximum air permeability according to the difference between the pressure difference of the parachute in the high-pressure difference environment and the critical pressure difference.

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